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![Hugh Dickins](/assets/img/avatar_default.png)
KSM needs a cond_resched() for CONFIG_PREEMPT_NONE, in its unbounded search of the unstable tree. The stable tree cases already have one, and originally there was one down inside get_user_pages(); but I missed it when I converted to follow_page() instead. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Acked-by: Izik Eidus <ieidus@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1710 lines
45 KiB
C
1710 lines
45 KiB
C
/*
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* Memory merging support.
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*
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* This code enables dynamic sharing of identical pages found in different
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* memory areas, even if they are not shared by fork()
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*
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* Copyright (C) 2008-2009 Red Hat, Inc.
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* Authors:
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* Izik Eidus
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* Andrea Arcangeli
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* Chris Wright
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* Hugh Dickins
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*
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* This work is licensed under the terms of the GNU GPL, version 2.
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*/
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#include <linux/errno.h>
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#include <linux/mm.h>
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#include <linux/fs.h>
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#include <linux/mman.h>
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#include <linux/sched.h>
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#include <linux/rwsem.h>
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#include <linux/pagemap.h>
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#include <linux/rmap.h>
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#include <linux/spinlock.h>
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#include <linux/jhash.h>
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#include <linux/delay.h>
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#include <linux/kthread.h>
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#include <linux/wait.h>
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#include <linux/slab.h>
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#include <linux/rbtree.h>
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#include <linux/mmu_notifier.h>
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#include <linux/swap.h>
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#include <linux/ksm.h>
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#include <asm/tlbflush.h>
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/*
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* A few notes about the KSM scanning process,
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* to make it easier to understand the data structures below:
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*
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* In order to reduce excessive scanning, KSM sorts the memory pages by their
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* contents into a data structure that holds pointers to the pages' locations.
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*
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* Since the contents of the pages may change at any moment, KSM cannot just
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* insert the pages into a normal sorted tree and expect it to find anything.
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* Therefore KSM uses two data structures - the stable and the unstable tree.
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*
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* The stable tree holds pointers to all the merged pages (ksm pages), sorted
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* by their contents. Because each such page is write-protected, searching on
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* this tree is fully assured to be working (except when pages are unmapped),
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* and therefore this tree is called the stable tree.
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*
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* In addition to the stable tree, KSM uses a second data structure called the
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* unstable tree: this tree holds pointers to pages which have been found to
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* be "unchanged for a period of time". The unstable tree sorts these pages
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* by their contents, but since they are not write-protected, KSM cannot rely
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* upon the unstable tree to work correctly - the unstable tree is liable to
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* be corrupted as its contents are modified, and so it is called unstable.
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*
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* KSM solves this problem by several techniques:
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*
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* 1) The unstable tree is flushed every time KSM completes scanning all
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* memory areas, and then the tree is rebuilt again from the beginning.
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* 2) KSM will only insert into the unstable tree, pages whose hash value
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* has not changed since the previous scan of all memory areas.
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* 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
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* colors of the nodes and not on their contents, assuring that even when
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* the tree gets "corrupted" it won't get out of balance, so scanning time
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* remains the same (also, searching and inserting nodes in an rbtree uses
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* the same algorithm, so we have no overhead when we flush and rebuild).
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* 4) KSM never flushes the stable tree, which means that even if it were to
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* take 10 attempts to find a page in the unstable tree, once it is found,
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* it is secured in the stable tree. (When we scan a new page, we first
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* compare it against the stable tree, and then against the unstable tree.)
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*/
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/**
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* struct mm_slot - ksm information per mm that is being scanned
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* @link: link to the mm_slots hash list
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* @mm_list: link into the mm_slots list, rooted in ksm_mm_head
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* @rmap_list: head for this mm_slot's list of rmap_items
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* @mm: the mm that this information is valid for
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*/
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struct mm_slot {
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struct hlist_node link;
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struct list_head mm_list;
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struct list_head rmap_list;
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struct mm_struct *mm;
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};
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/**
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* struct ksm_scan - cursor for scanning
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* @mm_slot: the current mm_slot we are scanning
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* @address: the next address inside that to be scanned
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* @rmap_item: the current rmap that we are scanning inside the rmap_list
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* @seqnr: count of completed full scans (needed when removing unstable node)
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*
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* There is only the one ksm_scan instance of this cursor structure.
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*/
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struct ksm_scan {
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struct mm_slot *mm_slot;
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unsigned long address;
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struct rmap_item *rmap_item;
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unsigned long seqnr;
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};
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/**
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* struct rmap_item - reverse mapping item for virtual addresses
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* @link: link into mm_slot's rmap_list (rmap_list is per mm)
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* @mm: the memory structure this rmap_item is pointing into
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* @address: the virtual address this rmap_item tracks (+ flags in low bits)
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* @oldchecksum: previous checksum of the page at that virtual address
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* @node: rb_node of this rmap_item in either unstable or stable tree
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* @next: next rmap_item hanging off the same node of the stable tree
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* @prev: previous rmap_item hanging off the same node of the stable tree
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*/
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struct rmap_item {
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struct list_head link;
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struct mm_struct *mm;
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unsigned long address; /* + low bits used for flags below */
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union {
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unsigned int oldchecksum; /* when unstable */
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struct rmap_item *next; /* when stable */
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};
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union {
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struct rb_node node; /* when tree node */
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struct rmap_item *prev; /* in stable list */
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};
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};
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#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
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#define NODE_FLAG 0x100 /* is a node of unstable or stable tree */
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#define STABLE_FLAG 0x200 /* is a node or list item of stable tree */
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/* The stable and unstable tree heads */
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static struct rb_root root_stable_tree = RB_ROOT;
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static struct rb_root root_unstable_tree = RB_ROOT;
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#define MM_SLOTS_HASH_HEADS 1024
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static struct hlist_head *mm_slots_hash;
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static struct mm_slot ksm_mm_head = {
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.mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
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};
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static struct ksm_scan ksm_scan = {
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.mm_slot = &ksm_mm_head,
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};
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static struct kmem_cache *rmap_item_cache;
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static struct kmem_cache *mm_slot_cache;
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/* The number of nodes in the stable tree */
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static unsigned long ksm_pages_shared;
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/* The number of page slots additionally sharing those nodes */
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static unsigned long ksm_pages_sharing;
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/* The number of nodes in the unstable tree */
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static unsigned long ksm_pages_unshared;
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/* The number of rmap_items in use: to calculate pages_volatile */
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static unsigned long ksm_rmap_items;
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/* Limit on the number of unswappable pages used */
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static unsigned long ksm_max_kernel_pages;
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/* Number of pages ksmd should scan in one batch */
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static unsigned int ksm_thread_pages_to_scan = 100;
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/* Milliseconds ksmd should sleep between batches */
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static unsigned int ksm_thread_sleep_millisecs = 20;
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#define KSM_RUN_STOP 0
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#define KSM_RUN_MERGE 1
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#define KSM_RUN_UNMERGE 2
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static unsigned int ksm_run = KSM_RUN_STOP;
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static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
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static DEFINE_MUTEX(ksm_thread_mutex);
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static DEFINE_SPINLOCK(ksm_mmlist_lock);
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#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
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sizeof(struct __struct), __alignof__(struct __struct),\
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(__flags), NULL)
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static int __init ksm_slab_init(void)
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{
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rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
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if (!rmap_item_cache)
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goto out;
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mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
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if (!mm_slot_cache)
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goto out_free;
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return 0;
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out_free:
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kmem_cache_destroy(rmap_item_cache);
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out:
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return -ENOMEM;
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}
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static void __init ksm_slab_free(void)
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{
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kmem_cache_destroy(mm_slot_cache);
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kmem_cache_destroy(rmap_item_cache);
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mm_slot_cache = NULL;
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}
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static inline struct rmap_item *alloc_rmap_item(void)
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{
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struct rmap_item *rmap_item;
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rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
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if (rmap_item)
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ksm_rmap_items++;
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return rmap_item;
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}
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static inline void free_rmap_item(struct rmap_item *rmap_item)
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{
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ksm_rmap_items--;
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rmap_item->mm = NULL; /* debug safety */
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kmem_cache_free(rmap_item_cache, rmap_item);
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}
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static inline struct mm_slot *alloc_mm_slot(void)
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{
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if (!mm_slot_cache) /* initialization failed */
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return NULL;
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return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
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}
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static inline void free_mm_slot(struct mm_slot *mm_slot)
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{
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kmem_cache_free(mm_slot_cache, mm_slot);
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}
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static int __init mm_slots_hash_init(void)
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{
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mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
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GFP_KERNEL);
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if (!mm_slots_hash)
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return -ENOMEM;
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return 0;
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}
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static void __init mm_slots_hash_free(void)
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{
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kfree(mm_slots_hash);
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}
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static struct mm_slot *get_mm_slot(struct mm_struct *mm)
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{
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struct mm_slot *mm_slot;
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struct hlist_head *bucket;
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struct hlist_node *node;
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bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
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% MM_SLOTS_HASH_HEADS];
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hlist_for_each_entry(mm_slot, node, bucket, link) {
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if (mm == mm_slot->mm)
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return mm_slot;
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}
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return NULL;
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}
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static void insert_to_mm_slots_hash(struct mm_struct *mm,
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struct mm_slot *mm_slot)
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{
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struct hlist_head *bucket;
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bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
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% MM_SLOTS_HASH_HEADS];
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mm_slot->mm = mm;
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INIT_LIST_HEAD(&mm_slot->rmap_list);
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hlist_add_head(&mm_slot->link, bucket);
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}
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static inline int in_stable_tree(struct rmap_item *rmap_item)
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{
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return rmap_item->address & STABLE_FLAG;
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}
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/*
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* ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
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* page tables after it has passed through ksm_exit() - which, if necessary,
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* takes mmap_sem briefly to serialize against them. ksm_exit() does not set
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* a special flag: they can just back out as soon as mm_users goes to zero.
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* ksm_test_exit() is used throughout to make this test for exit: in some
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* places for correctness, in some places just to avoid unnecessary work.
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*/
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static inline bool ksm_test_exit(struct mm_struct *mm)
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{
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return atomic_read(&mm->mm_users) == 0;
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}
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/*
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* We use break_ksm to break COW on a ksm page: it's a stripped down
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*
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* if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
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* put_page(page);
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*
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* but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
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* in case the application has unmapped and remapped mm,addr meanwhile.
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* Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
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* mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
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*/
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static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
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{
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struct page *page;
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int ret = 0;
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do {
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cond_resched();
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page = follow_page(vma, addr, FOLL_GET);
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if (!page)
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break;
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if (PageKsm(page))
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ret = handle_mm_fault(vma->vm_mm, vma, addr,
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FAULT_FLAG_WRITE);
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else
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ret = VM_FAULT_WRITE;
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put_page(page);
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} while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
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/*
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* We must loop because handle_mm_fault() may back out if there's
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* any difficulty e.g. if pte accessed bit gets updated concurrently.
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*
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* VM_FAULT_WRITE is what we have been hoping for: it indicates that
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* COW has been broken, even if the vma does not permit VM_WRITE;
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* but note that a concurrent fault might break PageKsm for us.
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*
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* VM_FAULT_SIGBUS could occur if we race with truncation of the
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* backing file, which also invalidates anonymous pages: that's
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* okay, that truncation will have unmapped the PageKsm for us.
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*
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* VM_FAULT_OOM: at the time of writing (late July 2009), setting
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* aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
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* current task has TIF_MEMDIE set, and will be OOM killed on return
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* to user; and ksmd, having no mm, would never be chosen for that.
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*
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* But if the mm is in a limited mem_cgroup, then the fault may fail
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* with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
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* even ksmd can fail in this way - though it's usually breaking ksm
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* just to undo a merge it made a moment before, so unlikely to oom.
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*
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* That's a pity: we might therefore have more kernel pages allocated
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* than we're counting as nodes in the stable tree; but ksm_do_scan
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* will retry to break_cow on each pass, so should recover the page
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* in due course. The important thing is to not let VM_MERGEABLE
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* be cleared while any such pages might remain in the area.
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*/
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return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
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}
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static void break_cow(struct mm_struct *mm, unsigned long addr)
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{
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struct vm_area_struct *vma;
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down_read(&mm->mmap_sem);
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if (ksm_test_exit(mm))
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goto out;
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vma = find_vma(mm, addr);
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if (!vma || vma->vm_start > addr)
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goto out;
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if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
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goto out;
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break_ksm(vma, addr);
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out:
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up_read(&mm->mmap_sem);
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}
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static struct page *get_mergeable_page(struct rmap_item *rmap_item)
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{
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struct mm_struct *mm = rmap_item->mm;
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unsigned long addr = rmap_item->address;
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struct vm_area_struct *vma;
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struct page *page;
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down_read(&mm->mmap_sem);
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if (ksm_test_exit(mm))
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goto out;
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vma = find_vma(mm, addr);
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if (!vma || vma->vm_start > addr)
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goto out;
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if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
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goto out;
|
|
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page = follow_page(vma, addr, FOLL_GET);
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if (!page)
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goto out;
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if (PageAnon(page)) {
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flush_anon_page(vma, page, addr);
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flush_dcache_page(page);
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} else {
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put_page(page);
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out: page = NULL;
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}
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up_read(&mm->mmap_sem);
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return page;
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}
|
|
|
|
/*
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* get_ksm_page: checks if the page at the virtual address in rmap_item
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* is still PageKsm, in which case we can trust the content of the page,
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* and it returns the gotten page; but NULL if the page has been zapped.
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*/
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static struct page *get_ksm_page(struct rmap_item *rmap_item)
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|
{
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struct page *page;
|
|
|
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page = get_mergeable_page(rmap_item);
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if (page && !PageKsm(page)) {
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put_page(page);
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page = NULL;
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}
|
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return page;
|
|
}
|
|
|
|
/*
|
|
* Removing rmap_item from stable or unstable tree.
|
|
* This function will clean the information from the stable/unstable tree.
|
|
*/
|
|
static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
|
|
{
|
|
if (in_stable_tree(rmap_item)) {
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|
struct rmap_item *next_item = rmap_item->next;
|
|
|
|
if (rmap_item->address & NODE_FLAG) {
|
|
if (next_item) {
|
|
rb_replace_node(&rmap_item->node,
|
|
&next_item->node,
|
|
&root_stable_tree);
|
|
next_item->address |= NODE_FLAG;
|
|
ksm_pages_sharing--;
|
|
} else {
|
|
rb_erase(&rmap_item->node, &root_stable_tree);
|
|
ksm_pages_shared--;
|
|
}
|
|
} else {
|
|
struct rmap_item *prev_item = rmap_item->prev;
|
|
|
|
BUG_ON(prev_item->next != rmap_item);
|
|
prev_item->next = next_item;
|
|
if (next_item) {
|
|
BUG_ON(next_item->prev != rmap_item);
|
|
next_item->prev = rmap_item->prev;
|
|
}
|
|
ksm_pages_sharing--;
|
|
}
|
|
|
|
rmap_item->next = NULL;
|
|
|
|
} else if (rmap_item->address & NODE_FLAG) {
|
|
unsigned char age;
|
|
/*
|
|
* Usually ksmd can and must skip the rb_erase, because
|
|
* root_unstable_tree was already reset to RB_ROOT.
|
|
* But be careful when an mm is exiting: do the rb_erase
|
|
* if this rmap_item was inserted by this scan, rather
|
|
* than left over from before.
|
|
*/
|
|
age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
|
|
BUG_ON(age > 1);
|
|
if (!age)
|
|
rb_erase(&rmap_item->node, &root_unstable_tree);
|
|
ksm_pages_unshared--;
|
|
}
|
|
|
|
rmap_item->address &= PAGE_MASK;
|
|
|
|
cond_resched(); /* we're called from many long loops */
|
|
}
|
|
|
|
static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
|
|
struct list_head *cur)
|
|
{
|
|
struct rmap_item *rmap_item;
|
|
|
|
while (cur != &mm_slot->rmap_list) {
|
|
rmap_item = list_entry(cur, struct rmap_item, link);
|
|
cur = cur->next;
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
list_del(&rmap_item->link);
|
|
free_rmap_item(rmap_item);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
|
|
* than check every pte of a given vma, the locking doesn't quite work for
|
|
* that - an rmap_item is assigned to the stable tree after inserting ksm
|
|
* page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
|
|
* rmap_items from parent to child at fork time (so as not to waste time
|
|
* if exit comes before the next scan reaches it).
|
|
*
|
|
* Similarly, although we'd like to remove rmap_items (so updating counts
|
|
* and freeing memory) when unmerging an area, it's easier to leave that
|
|
* to the next pass of ksmd - consider, for example, how ksmd might be
|
|
* in cmp_and_merge_page on one of the rmap_items we would be removing.
|
|
*/
|
|
static int unmerge_ksm_pages(struct vm_area_struct *vma,
|
|
unsigned long start, unsigned long end)
|
|
{
|
|
unsigned long addr;
|
|
int err = 0;
|
|
|
|
for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
|
|
if (ksm_test_exit(vma->vm_mm))
|
|
break;
|
|
if (signal_pending(current))
|
|
err = -ERESTARTSYS;
|
|
else
|
|
err = break_ksm(vma, addr);
|
|
}
|
|
return err;
|
|
}
|
|
|
|
#ifdef CONFIG_SYSFS
|
|
/*
|
|
* Only called through the sysfs control interface:
|
|
*/
|
|
static int unmerge_and_remove_all_rmap_items(void)
|
|
{
|
|
struct mm_slot *mm_slot;
|
|
struct mm_struct *mm;
|
|
struct vm_area_struct *vma;
|
|
int err = 0;
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
|
|
struct mm_slot, mm_list);
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
for (mm_slot = ksm_scan.mm_slot;
|
|
mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
|
|
mm = mm_slot->mm;
|
|
down_read(&mm->mmap_sem);
|
|
for (vma = mm->mmap; vma; vma = vma->vm_next) {
|
|
if (ksm_test_exit(mm))
|
|
break;
|
|
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
|
|
continue;
|
|
err = unmerge_ksm_pages(vma,
|
|
vma->vm_start, vma->vm_end);
|
|
if (err)
|
|
goto error;
|
|
}
|
|
|
|
remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
|
|
struct mm_slot, mm_list);
|
|
if (ksm_test_exit(mm)) {
|
|
hlist_del(&mm_slot->link);
|
|
list_del(&mm_slot->mm_list);
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
free_mm_slot(mm_slot);
|
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
up_read(&mm->mmap_sem);
|
|
mmdrop(mm);
|
|
} else {
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
up_read(&mm->mmap_sem);
|
|
}
|
|
}
|
|
|
|
ksm_scan.seqnr = 0;
|
|
return 0;
|
|
|
|
error:
|
|
up_read(&mm->mmap_sem);
|
|
spin_lock(&ksm_mmlist_lock);
|
|
ksm_scan.mm_slot = &ksm_mm_head;
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
return err;
|
|
}
|
|
#endif /* CONFIG_SYSFS */
|
|
|
|
static u32 calc_checksum(struct page *page)
|
|
{
|
|
u32 checksum;
|
|
void *addr = kmap_atomic(page, KM_USER0);
|
|
checksum = jhash2(addr, PAGE_SIZE / 4, 17);
|
|
kunmap_atomic(addr, KM_USER0);
|
|
return checksum;
|
|
}
|
|
|
|
static int memcmp_pages(struct page *page1, struct page *page2)
|
|
{
|
|
char *addr1, *addr2;
|
|
int ret;
|
|
|
|
addr1 = kmap_atomic(page1, KM_USER0);
|
|
addr2 = kmap_atomic(page2, KM_USER1);
|
|
ret = memcmp(addr1, addr2, PAGE_SIZE);
|
|
kunmap_atomic(addr2, KM_USER1);
|
|
kunmap_atomic(addr1, KM_USER0);
|
|
return ret;
|
|
}
|
|
|
|
static inline int pages_identical(struct page *page1, struct page *page2)
|
|
{
|
|
return !memcmp_pages(page1, page2);
|
|
}
|
|
|
|
static int write_protect_page(struct vm_area_struct *vma, struct page *page,
|
|
pte_t *orig_pte)
|
|
{
|
|
struct mm_struct *mm = vma->vm_mm;
|
|
unsigned long addr;
|
|
pte_t *ptep;
|
|
spinlock_t *ptl;
|
|
int swapped;
|
|
int err = -EFAULT;
|
|
|
|
addr = page_address_in_vma(page, vma);
|
|
if (addr == -EFAULT)
|
|
goto out;
|
|
|
|
ptep = page_check_address(page, mm, addr, &ptl, 0);
|
|
if (!ptep)
|
|
goto out;
|
|
|
|
if (pte_write(*ptep)) {
|
|
pte_t entry;
|
|
|
|
swapped = PageSwapCache(page);
|
|
flush_cache_page(vma, addr, page_to_pfn(page));
|
|
/*
|
|
* Ok this is tricky, when get_user_pages_fast() run it doesnt
|
|
* take any lock, therefore the check that we are going to make
|
|
* with the pagecount against the mapcount is racey and
|
|
* O_DIRECT can happen right after the check.
|
|
* So we clear the pte and flush the tlb before the check
|
|
* this assure us that no O_DIRECT can happen after the check
|
|
* or in the middle of the check.
|
|
*/
|
|
entry = ptep_clear_flush(vma, addr, ptep);
|
|
/*
|
|
* Check that no O_DIRECT or similar I/O is in progress on the
|
|
* page
|
|
*/
|
|
if ((page_mapcount(page) + 2 + swapped) != page_count(page)) {
|
|
set_pte_at_notify(mm, addr, ptep, entry);
|
|
goto out_unlock;
|
|
}
|
|
entry = pte_wrprotect(entry);
|
|
set_pte_at_notify(mm, addr, ptep, entry);
|
|
}
|
|
*orig_pte = *ptep;
|
|
err = 0;
|
|
|
|
out_unlock:
|
|
pte_unmap_unlock(ptep, ptl);
|
|
out:
|
|
return err;
|
|
}
|
|
|
|
/**
|
|
* replace_page - replace page in vma by new ksm page
|
|
* @vma: vma that holds the pte pointing to oldpage
|
|
* @oldpage: the page we are replacing by newpage
|
|
* @newpage: the ksm page we replace oldpage by
|
|
* @orig_pte: the original value of the pte
|
|
*
|
|
* Returns 0 on success, -EFAULT on failure.
|
|
*/
|
|
static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
|
|
struct page *newpage, pte_t orig_pte)
|
|
{
|
|
struct mm_struct *mm = vma->vm_mm;
|
|
pgd_t *pgd;
|
|
pud_t *pud;
|
|
pmd_t *pmd;
|
|
pte_t *ptep;
|
|
spinlock_t *ptl;
|
|
unsigned long addr;
|
|
pgprot_t prot;
|
|
int err = -EFAULT;
|
|
|
|
prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE);
|
|
|
|
addr = page_address_in_vma(oldpage, vma);
|
|
if (addr == -EFAULT)
|
|
goto out;
|
|
|
|
pgd = pgd_offset(mm, addr);
|
|
if (!pgd_present(*pgd))
|
|
goto out;
|
|
|
|
pud = pud_offset(pgd, addr);
|
|
if (!pud_present(*pud))
|
|
goto out;
|
|
|
|
pmd = pmd_offset(pud, addr);
|
|
if (!pmd_present(*pmd))
|
|
goto out;
|
|
|
|
ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
|
|
if (!pte_same(*ptep, orig_pte)) {
|
|
pte_unmap_unlock(ptep, ptl);
|
|
goto out;
|
|
}
|
|
|
|
get_page(newpage);
|
|
page_add_ksm_rmap(newpage);
|
|
|
|
flush_cache_page(vma, addr, pte_pfn(*ptep));
|
|
ptep_clear_flush(vma, addr, ptep);
|
|
set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot));
|
|
|
|
page_remove_rmap(oldpage);
|
|
put_page(oldpage);
|
|
|
|
pte_unmap_unlock(ptep, ptl);
|
|
err = 0;
|
|
out:
|
|
return err;
|
|
}
|
|
|
|
/*
|
|
* try_to_merge_one_page - take two pages and merge them into one
|
|
* @vma: the vma that hold the pte pointing into oldpage
|
|
* @oldpage: the page that we want to replace with newpage
|
|
* @newpage: the page that we want to map instead of oldpage
|
|
*
|
|
* Note:
|
|
* oldpage should be a PageAnon page, while newpage should be a PageKsm page,
|
|
* or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm.
|
|
*
|
|
* This function returns 0 if the pages were merged, -EFAULT otherwise.
|
|
*/
|
|
static int try_to_merge_one_page(struct vm_area_struct *vma,
|
|
struct page *oldpage,
|
|
struct page *newpage)
|
|
{
|
|
pte_t orig_pte = __pte(0);
|
|
int err = -EFAULT;
|
|
|
|
if (!(vma->vm_flags & VM_MERGEABLE))
|
|
goto out;
|
|
|
|
if (!PageAnon(oldpage))
|
|
goto out;
|
|
|
|
get_page(newpage);
|
|
get_page(oldpage);
|
|
|
|
/*
|
|
* We need the page lock to read a stable PageSwapCache in
|
|
* write_protect_page(). We use trylock_page() instead of
|
|
* lock_page() because we don't want to wait here - we
|
|
* prefer to continue scanning and merging different pages,
|
|
* then come back to this page when it is unlocked.
|
|
*/
|
|
if (!trylock_page(oldpage))
|
|
goto out_putpage;
|
|
/*
|
|
* If this anonymous page is mapped only here, its pte may need
|
|
* to be write-protected. If it's mapped elsewhere, all of its
|
|
* ptes are necessarily already write-protected. But in either
|
|
* case, we need to lock and check page_count is not raised.
|
|
*/
|
|
if (write_protect_page(vma, oldpage, &orig_pte)) {
|
|
unlock_page(oldpage);
|
|
goto out_putpage;
|
|
}
|
|
unlock_page(oldpage);
|
|
|
|
if (pages_identical(oldpage, newpage))
|
|
err = replace_page(vma, oldpage, newpage, orig_pte);
|
|
|
|
out_putpage:
|
|
put_page(oldpage);
|
|
put_page(newpage);
|
|
out:
|
|
return err;
|
|
}
|
|
|
|
/*
|
|
* try_to_merge_with_ksm_page - like try_to_merge_two_pages,
|
|
* but no new kernel page is allocated: kpage must already be a ksm page.
|
|
*/
|
|
static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
|
|
unsigned long addr1,
|
|
struct page *page1,
|
|
struct page *kpage)
|
|
{
|
|
struct vm_area_struct *vma;
|
|
int err = -EFAULT;
|
|
|
|
down_read(&mm1->mmap_sem);
|
|
if (ksm_test_exit(mm1))
|
|
goto out;
|
|
|
|
vma = find_vma(mm1, addr1);
|
|
if (!vma || vma->vm_start > addr1)
|
|
goto out;
|
|
|
|
err = try_to_merge_one_page(vma, page1, kpage);
|
|
out:
|
|
up_read(&mm1->mmap_sem);
|
|
return err;
|
|
}
|
|
|
|
/*
|
|
* try_to_merge_two_pages - take two identical pages and prepare them
|
|
* to be merged into one page.
|
|
*
|
|
* This function returns 0 if we successfully mapped two identical pages
|
|
* into one page, -EFAULT otherwise.
|
|
*
|
|
* Note that this function allocates a new kernel page: if one of the pages
|
|
* is already a ksm page, try_to_merge_with_ksm_page should be used.
|
|
*/
|
|
static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
|
|
struct page *page1, struct mm_struct *mm2,
|
|
unsigned long addr2, struct page *page2)
|
|
{
|
|
struct vm_area_struct *vma;
|
|
struct page *kpage;
|
|
int err = -EFAULT;
|
|
|
|
/*
|
|
* The number of nodes in the stable tree
|
|
* is the number of kernel pages that we hold.
|
|
*/
|
|
if (ksm_max_kernel_pages &&
|
|
ksm_max_kernel_pages <= ksm_pages_shared)
|
|
return err;
|
|
|
|
kpage = alloc_page(GFP_HIGHUSER);
|
|
if (!kpage)
|
|
return err;
|
|
|
|
down_read(&mm1->mmap_sem);
|
|
if (ksm_test_exit(mm1)) {
|
|
up_read(&mm1->mmap_sem);
|
|
goto out;
|
|
}
|
|
vma = find_vma(mm1, addr1);
|
|
if (!vma || vma->vm_start > addr1) {
|
|
up_read(&mm1->mmap_sem);
|
|
goto out;
|
|
}
|
|
|
|
copy_user_highpage(kpage, page1, addr1, vma);
|
|
err = try_to_merge_one_page(vma, page1, kpage);
|
|
up_read(&mm1->mmap_sem);
|
|
|
|
if (!err) {
|
|
err = try_to_merge_with_ksm_page(mm2, addr2, page2, kpage);
|
|
/*
|
|
* If that fails, we have a ksm page with only one pte
|
|
* pointing to it: so break it.
|
|
*/
|
|
if (err)
|
|
break_cow(mm1, addr1);
|
|
}
|
|
out:
|
|
put_page(kpage);
|
|
return err;
|
|
}
|
|
|
|
/*
|
|
* stable_tree_search - search page inside the stable tree
|
|
* @page: the page that we are searching identical pages to.
|
|
* @page2: pointer into identical page that we are holding inside the stable
|
|
* tree that we have found.
|
|
* @rmap_item: the reverse mapping item
|
|
*
|
|
* This function checks if there is a page inside the stable tree
|
|
* with identical content to the page that we are scanning right now.
|
|
*
|
|
* This function return rmap_item pointer to the identical item if found,
|
|
* NULL otherwise.
|
|
*/
|
|
static struct rmap_item *stable_tree_search(struct page *page,
|
|
struct page **page2,
|
|
struct rmap_item *rmap_item)
|
|
{
|
|
struct rb_node *node = root_stable_tree.rb_node;
|
|
|
|
while (node) {
|
|
struct rmap_item *tree_rmap_item, *next_rmap_item;
|
|
int ret;
|
|
|
|
tree_rmap_item = rb_entry(node, struct rmap_item, node);
|
|
while (tree_rmap_item) {
|
|
BUG_ON(!in_stable_tree(tree_rmap_item));
|
|
cond_resched();
|
|
page2[0] = get_ksm_page(tree_rmap_item);
|
|
if (page2[0])
|
|
break;
|
|
next_rmap_item = tree_rmap_item->next;
|
|
remove_rmap_item_from_tree(tree_rmap_item);
|
|
tree_rmap_item = next_rmap_item;
|
|
}
|
|
if (!tree_rmap_item)
|
|
return NULL;
|
|
|
|
ret = memcmp_pages(page, page2[0]);
|
|
|
|
if (ret < 0) {
|
|
put_page(page2[0]);
|
|
node = node->rb_left;
|
|
} else if (ret > 0) {
|
|
put_page(page2[0]);
|
|
node = node->rb_right;
|
|
} else {
|
|
return tree_rmap_item;
|
|
}
|
|
}
|
|
|
|
return NULL;
|
|
}
|
|
|
|
/*
|
|
* stable_tree_insert - insert rmap_item pointing to new ksm page
|
|
* into the stable tree.
|
|
*
|
|
* @page: the page that we are searching identical page to inside the stable
|
|
* tree.
|
|
* @rmap_item: pointer to the reverse mapping item.
|
|
*
|
|
* This function returns rmap_item if success, NULL otherwise.
|
|
*/
|
|
static struct rmap_item *stable_tree_insert(struct page *page,
|
|
struct rmap_item *rmap_item)
|
|
{
|
|
struct rb_node **new = &root_stable_tree.rb_node;
|
|
struct rb_node *parent = NULL;
|
|
|
|
while (*new) {
|
|
struct rmap_item *tree_rmap_item, *next_rmap_item;
|
|
struct page *tree_page;
|
|
int ret;
|
|
|
|
tree_rmap_item = rb_entry(*new, struct rmap_item, node);
|
|
while (tree_rmap_item) {
|
|
BUG_ON(!in_stable_tree(tree_rmap_item));
|
|
cond_resched();
|
|
tree_page = get_ksm_page(tree_rmap_item);
|
|
if (tree_page)
|
|
break;
|
|
next_rmap_item = tree_rmap_item->next;
|
|
remove_rmap_item_from_tree(tree_rmap_item);
|
|
tree_rmap_item = next_rmap_item;
|
|
}
|
|
if (!tree_rmap_item)
|
|
return NULL;
|
|
|
|
ret = memcmp_pages(page, tree_page);
|
|
put_page(tree_page);
|
|
|
|
parent = *new;
|
|
if (ret < 0)
|
|
new = &parent->rb_left;
|
|
else if (ret > 0)
|
|
new = &parent->rb_right;
|
|
else {
|
|
/*
|
|
* It is not a bug that stable_tree_search() didn't
|
|
* find this node: because at that time our page was
|
|
* not yet write-protected, so may have changed since.
|
|
*/
|
|
return NULL;
|
|
}
|
|
}
|
|
|
|
rmap_item->address |= NODE_FLAG | STABLE_FLAG;
|
|
rmap_item->next = NULL;
|
|
rb_link_node(&rmap_item->node, parent, new);
|
|
rb_insert_color(&rmap_item->node, &root_stable_tree);
|
|
|
|
ksm_pages_shared++;
|
|
return rmap_item;
|
|
}
|
|
|
|
/*
|
|
* unstable_tree_search_insert - search and insert items into the unstable tree.
|
|
*
|
|
* @page: the page that we are going to search for identical page or to insert
|
|
* into the unstable tree
|
|
* @page2: pointer into identical page that was found inside the unstable tree
|
|
* @rmap_item: the reverse mapping item of page
|
|
*
|
|
* This function searches for a page in the unstable tree identical to the
|
|
* page currently being scanned; and if no identical page is found in the
|
|
* tree, we insert rmap_item as a new object into the unstable tree.
|
|
*
|
|
* This function returns pointer to rmap_item found to be identical
|
|
* to the currently scanned page, NULL otherwise.
|
|
*
|
|
* This function does both searching and inserting, because they share
|
|
* the same walking algorithm in an rbtree.
|
|
*/
|
|
static struct rmap_item *unstable_tree_search_insert(struct page *page,
|
|
struct page **page2,
|
|
struct rmap_item *rmap_item)
|
|
{
|
|
struct rb_node **new = &root_unstable_tree.rb_node;
|
|
struct rb_node *parent = NULL;
|
|
|
|
while (*new) {
|
|
struct rmap_item *tree_rmap_item;
|
|
int ret;
|
|
|
|
cond_resched();
|
|
tree_rmap_item = rb_entry(*new, struct rmap_item, node);
|
|
page2[0] = get_mergeable_page(tree_rmap_item);
|
|
if (!page2[0])
|
|
return NULL;
|
|
|
|
/*
|
|
* Don't substitute an unswappable ksm page
|
|
* just for one good swappable forked page.
|
|
*/
|
|
if (page == page2[0]) {
|
|
put_page(page2[0]);
|
|
return NULL;
|
|
}
|
|
|
|
ret = memcmp_pages(page, page2[0]);
|
|
|
|
parent = *new;
|
|
if (ret < 0) {
|
|
put_page(page2[0]);
|
|
new = &parent->rb_left;
|
|
} else if (ret > 0) {
|
|
put_page(page2[0]);
|
|
new = &parent->rb_right;
|
|
} else {
|
|
return tree_rmap_item;
|
|
}
|
|
}
|
|
|
|
rmap_item->address |= NODE_FLAG;
|
|
rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
|
|
rb_link_node(&rmap_item->node, parent, new);
|
|
rb_insert_color(&rmap_item->node, &root_unstable_tree);
|
|
|
|
ksm_pages_unshared++;
|
|
return NULL;
|
|
}
|
|
|
|
/*
|
|
* stable_tree_append - add another rmap_item to the linked list of
|
|
* rmap_items hanging off a given node of the stable tree, all sharing
|
|
* the same ksm page.
|
|
*/
|
|
static void stable_tree_append(struct rmap_item *rmap_item,
|
|
struct rmap_item *tree_rmap_item)
|
|
{
|
|
rmap_item->next = tree_rmap_item->next;
|
|
rmap_item->prev = tree_rmap_item;
|
|
|
|
if (tree_rmap_item->next)
|
|
tree_rmap_item->next->prev = rmap_item;
|
|
|
|
tree_rmap_item->next = rmap_item;
|
|
rmap_item->address |= STABLE_FLAG;
|
|
|
|
ksm_pages_sharing++;
|
|
}
|
|
|
|
/*
|
|
* cmp_and_merge_page - first see if page can be merged into the stable tree;
|
|
* if not, compare checksum to previous and if it's the same, see if page can
|
|
* be inserted into the unstable tree, or merged with a page already there and
|
|
* both transferred to the stable tree.
|
|
*
|
|
* @page: the page that we are searching identical page to.
|
|
* @rmap_item: the reverse mapping into the virtual address of this page
|
|
*/
|
|
static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
|
|
{
|
|
struct page *page2[1];
|
|
struct rmap_item *tree_rmap_item;
|
|
unsigned int checksum;
|
|
int err;
|
|
|
|
if (in_stable_tree(rmap_item))
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
|
|
/* We first start with searching the page inside the stable tree */
|
|
tree_rmap_item = stable_tree_search(page, page2, rmap_item);
|
|
if (tree_rmap_item) {
|
|
if (page == page2[0]) /* forked */
|
|
err = 0;
|
|
else
|
|
err = try_to_merge_with_ksm_page(rmap_item->mm,
|
|
rmap_item->address,
|
|
page, page2[0]);
|
|
put_page(page2[0]);
|
|
|
|
if (!err) {
|
|
/*
|
|
* The page was successfully merged:
|
|
* add its rmap_item to the stable tree.
|
|
*/
|
|
stable_tree_append(rmap_item, tree_rmap_item);
|
|
}
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* A ksm page might have got here by fork, but its other
|
|
* references have already been removed from the stable tree.
|
|
* Or it might be left over from a break_ksm which failed
|
|
* when the mem_cgroup had reached its limit: try again now.
|
|
*/
|
|
if (PageKsm(page))
|
|
break_cow(rmap_item->mm, rmap_item->address);
|
|
|
|
/*
|
|
* In case the hash value of the page was changed from the last time we
|
|
* have calculated it, this page to be changed frequely, therefore we
|
|
* don't want to insert it to the unstable tree, and we don't want to
|
|
* waste our time to search if there is something identical to it there.
|
|
*/
|
|
checksum = calc_checksum(page);
|
|
if (rmap_item->oldchecksum != checksum) {
|
|
rmap_item->oldchecksum = checksum;
|
|
return;
|
|
}
|
|
|
|
tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item);
|
|
if (tree_rmap_item) {
|
|
err = try_to_merge_two_pages(rmap_item->mm,
|
|
rmap_item->address, page,
|
|
tree_rmap_item->mm,
|
|
tree_rmap_item->address, page2[0]);
|
|
/*
|
|
* As soon as we merge this page, we want to remove the
|
|
* rmap_item of the page we have merged with from the unstable
|
|
* tree, and insert it instead as new node in the stable tree.
|
|
*/
|
|
if (!err) {
|
|
rb_erase(&tree_rmap_item->node, &root_unstable_tree);
|
|
tree_rmap_item->address &= ~NODE_FLAG;
|
|
ksm_pages_unshared--;
|
|
|
|
/*
|
|
* If we fail to insert the page into the stable tree,
|
|
* we will have 2 virtual addresses that are pointing
|
|
* to a ksm page left outside the stable tree,
|
|
* in which case we need to break_cow on both.
|
|
*/
|
|
if (stable_tree_insert(page2[0], tree_rmap_item))
|
|
stable_tree_append(rmap_item, tree_rmap_item);
|
|
else {
|
|
break_cow(tree_rmap_item->mm,
|
|
tree_rmap_item->address);
|
|
break_cow(rmap_item->mm, rmap_item->address);
|
|
}
|
|
}
|
|
|
|
put_page(page2[0]);
|
|
}
|
|
}
|
|
|
|
static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
|
|
struct list_head *cur,
|
|
unsigned long addr)
|
|
{
|
|
struct rmap_item *rmap_item;
|
|
|
|
while (cur != &mm_slot->rmap_list) {
|
|
rmap_item = list_entry(cur, struct rmap_item, link);
|
|
if ((rmap_item->address & PAGE_MASK) == addr) {
|
|
if (!in_stable_tree(rmap_item))
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
return rmap_item;
|
|
}
|
|
if (rmap_item->address > addr)
|
|
break;
|
|
cur = cur->next;
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
list_del(&rmap_item->link);
|
|
free_rmap_item(rmap_item);
|
|
}
|
|
|
|
rmap_item = alloc_rmap_item();
|
|
if (rmap_item) {
|
|
/* It has already been zeroed */
|
|
rmap_item->mm = mm_slot->mm;
|
|
rmap_item->address = addr;
|
|
list_add_tail(&rmap_item->link, cur);
|
|
}
|
|
return rmap_item;
|
|
}
|
|
|
|
static struct rmap_item *scan_get_next_rmap_item(struct page **page)
|
|
{
|
|
struct mm_struct *mm;
|
|
struct mm_slot *slot;
|
|
struct vm_area_struct *vma;
|
|
struct rmap_item *rmap_item;
|
|
|
|
if (list_empty(&ksm_mm_head.mm_list))
|
|
return NULL;
|
|
|
|
slot = ksm_scan.mm_slot;
|
|
if (slot == &ksm_mm_head) {
|
|
root_unstable_tree = RB_ROOT;
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
|
|
ksm_scan.mm_slot = slot;
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
next_mm:
|
|
ksm_scan.address = 0;
|
|
ksm_scan.rmap_item = list_entry(&slot->rmap_list,
|
|
struct rmap_item, link);
|
|
}
|
|
|
|
mm = slot->mm;
|
|
down_read(&mm->mmap_sem);
|
|
if (ksm_test_exit(mm))
|
|
vma = NULL;
|
|
else
|
|
vma = find_vma(mm, ksm_scan.address);
|
|
|
|
for (; vma; vma = vma->vm_next) {
|
|
if (!(vma->vm_flags & VM_MERGEABLE))
|
|
continue;
|
|
if (ksm_scan.address < vma->vm_start)
|
|
ksm_scan.address = vma->vm_start;
|
|
if (!vma->anon_vma)
|
|
ksm_scan.address = vma->vm_end;
|
|
|
|
while (ksm_scan.address < vma->vm_end) {
|
|
if (ksm_test_exit(mm))
|
|
break;
|
|
*page = follow_page(vma, ksm_scan.address, FOLL_GET);
|
|
if (*page && PageAnon(*page)) {
|
|
flush_anon_page(vma, *page, ksm_scan.address);
|
|
flush_dcache_page(*page);
|
|
rmap_item = get_next_rmap_item(slot,
|
|
ksm_scan.rmap_item->link.next,
|
|
ksm_scan.address);
|
|
if (rmap_item) {
|
|
ksm_scan.rmap_item = rmap_item;
|
|
ksm_scan.address += PAGE_SIZE;
|
|
} else
|
|
put_page(*page);
|
|
up_read(&mm->mmap_sem);
|
|
return rmap_item;
|
|
}
|
|
if (*page)
|
|
put_page(*page);
|
|
ksm_scan.address += PAGE_SIZE;
|
|
cond_resched();
|
|
}
|
|
}
|
|
|
|
if (ksm_test_exit(mm)) {
|
|
ksm_scan.address = 0;
|
|
ksm_scan.rmap_item = list_entry(&slot->rmap_list,
|
|
struct rmap_item, link);
|
|
}
|
|
/*
|
|
* Nuke all the rmap_items that are above this current rmap:
|
|
* because there were no VM_MERGEABLE vmas with such addresses.
|
|
*/
|
|
remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
ksm_scan.mm_slot = list_entry(slot->mm_list.next,
|
|
struct mm_slot, mm_list);
|
|
if (ksm_scan.address == 0) {
|
|
/*
|
|
* We've completed a full scan of all vmas, holding mmap_sem
|
|
* throughout, and found no VM_MERGEABLE: so do the same as
|
|
* __ksm_exit does to remove this mm from all our lists now.
|
|
* This applies either when cleaning up after __ksm_exit
|
|
* (but beware: we can reach here even before __ksm_exit),
|
|
* or when all VM_MERGEABLE areas have been unmapped (and
|
|
* mmap_sem then protects against race with MADV_MERGEABLE).
|
|
*/
|
|
hlist_del(&slot->link);
|
|
list_del(&slot->mm_list);
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
free_mm_slot(slot);
|
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
up_read(&mm->mmap_sem);
|
|
mmdrop(mm);
|
|
} else {
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
up_read(&mm->mmap_sem);
|
|
}
|
|
|
|
/* Repeat until we've completed scanning the whole list */
|
|
slot = ksm_scan.mm_slot;
|
|
if (slot != &ksm_mm_head)
|
|
goto next_mm;
|
|
|
|
ksm_scan.seqnr++;
|
|
return NULL;
|
|
}
|
|
|
|
/**
|
|
* ksm_do_scan - the ksm scanner main worker function.
|
|
* @scan_npages - number of pages we want to scan before we return.
|
|
*/
|
|
static void ksm_do_scan(unsigned int scan_npages)
|
|
{
|
|
struct rmap_item *rmap_item;
|
|
struct page *page;
|
|
|
|
while (scan_npages--) {
|
|
cond_resched();
|
|
rmap_item = scan_get_next_rmap_item(&page);
|
|
if (!rmap_item)
|
|
return;
|
|
if (!PageKsm(page) || !in_stable_tree(rmap_item))
|
|
cmp_and_merge_page(page, rmap_item);
|
|
else if (page_mapcount(page) == 1) {
|
|
/*
|
|
* Replace now-unshared ksm page by ordinary page.
|
|
*/
|
|
break_cow(rmap_item->mm, rmap_item->address);
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
rmap_item->oldchecksum = calc_checksum(page);
|
|
}
|
|
put_page(page);
|
|
}
|
|
}
|
|
|
|
static int ksmd_should_run(void)
|
|
{
|
|
return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
|
|
}
|
|
|
|
static int ksm_scan_thread(void *nothing)
|
|
{
|
|
set_user_nice(current, 5);
|
|
|
|
while (!kthread_should_stop()) {
|
|
mutex_lock(&ksm_thread_mutex);
|
|
if (ksmd_should_run())
|
|
ksm_do_scan(ksm_thread_pages_to_scan);
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
if (ksmd_should_run()) {
|
|
schedule_timeout_interruptible(
|
|
msecs_to_jiffies(ksm_thread_sleep_millisecs));
|
|
} else {
|
|
wait_event_interruptible(ksm_thread_wait,
|
|
ksmd_should_run() || kthread_should_stop());
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
|
|
unsigned long end, int advice, unsigned long *vm_flags)
|
|
{
|
|
struct mm_struct *mm = vma->vm_mm;
|
|
int err;
|
|
|
|
switch (advice) {
|
|
case MADV_MERGEABLE:
|
|
/*
|
|
* Be somewhat over-protective for now!
|
|
*/
|
|
if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
|
|
VM_PFNMAP | VM_IO | VM_DONTEXPAND |
|
|
VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
|
|
VM_MIXEDMAP | VM_SAO))
|
|
return 0; /* just ignore the advice */
|
|
|
|
if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
|
|
err = __ksm_enter(mm);
|
|
if (err)
|
|
return err;
|
|
}
|
|
|
|
*vm_flags |= VM_MERGEABLE;
|
|
break;
|
|
|
|
case MADV_UNMERGEABLE:
|
|
if (!(*vm_flags & VM_MERGEABLE))
|
|
return 0; /* just ignore the advice */
|
|
|
|
if (vma->anon_vma) {
|
|
err = unmerge_ksm_pages(vma, start, end);
|
|
if (err)
|
|
return err;
|
|
}
|
|
|
|
*vm_flags &= ~VM_MERGEABLE;
|
|
break;
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
int __ksm_enter(struct mm_struct *mm)
|
|
{
|
|
struct mm_slot *mm_slot;
|
|
int needs_wakeup;
|
|
|
|
mm_slot = alloc_mm_slot();
|
|
if (!mm_slot)
|
|
return -ENOMEM;
|
|
|
|
/* Check ksm_run too? Would need tighter locking */
|
|
needs_wakeup = list_empty(&ksm_mm_head.mm_list);
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
insert_to_mm_slots_hash(mm, mm_slot);
|
|
/*
|
|
* Insert just behind the scanning cursor, to let the area settle
|
|
* down a little; when fork is followed by immediate exec, we don't
|
|
* want ksmd to waste time setting up and tearing down an rmap_list.
|
|
*/
|
|
list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
set_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
atomic_inc(&mm->mm_count);
|
|
|
|
if (needs_wakeup)
|
|
wake_up_interruptible(&ksm_thread_wait);
|
|
|
|
return 0;
|
|
}
|
|
|
|
void __ksm_exit(struct mm_struct *mm)
|
|
{
|
|
struct mm_slot *mm_slot;
|
|
int easy_to_free = 0;
|
|
|
|
/*
|
|
* This process is exiting: if it's straightforward (as is the
|
|
* case when ksmd was never running), free mm_slot immediately.
|
|
* But if it's at the cursor or has rmap_items linked to it, use
|
|
* mmap_sem to synchronize with any break_cows before pagetables
|
|
* are freed, and leave the mm_slot on the list for ksmd to free.
|
|
* Beware: ksm may already have noticed it exiting and freed the slot.
|
|
*/
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
mm_slot = get_mm_slot(mm);
|
|
if (mm_slot && ksm_scan.mm_slot != mm_slot) {
|
|
if (list_empty(&mm_slot->rmap_list)) {
|
|
hlist_del(&mm_slot->link);
|
|
list_del(&mm_slot->mm_list);
|
|
easy_to_free = 1;
|
|
} else {
|
|
list_move(&mm_slot->mm_list,
|
|
&ksm_scan.mm_slot->mm_list);
|
|
}
|
|
}
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
if (easy_to_free) {
|
|
free_mm_slot(mm_slot);
|
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
mmdrop(mm);
|
|
} else if (mm_slot) {
|
|
down_write(&mm->mmap_sem);
|
|
up_write(&mm->mmap_sem);
|
|
}
|
|
}
|
|
|
|
#ifdef CONFIG_SYSFS
|
|
/*
|
|
* This all compiles without CONFIG_SYSFS, but is a waste of space.
|
|
*/
|
|
|
|
#define KSM_ATTR_RO(_name) \
|
|
static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
|
|
#define KSM_ATTR(_name) \
|
|
static struct kobj_attribute _name##_attr = \
|
|
__ATTR(_name, 0644, _name##_show, _name##_store)
|
|
|
|
static ssize_t sleep_millisecs_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
|
|
}
|
|
|
|
static ssize_t sleep_millisecs_store(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
unsigned long msecs;
|
|
int err;
|
|
|
|
err = strict_strtoul(buf, 10, &msecs);
|
|
if (err || msecs > UINT_MAX)
|
|
return -EINVAL;
|
|
|
|
ksm_thread_sleep_millisecs = msecs;
|
|
|
|
return count;
|
|
}
|
|
KSM_ATTR(sleep_millisecs);
|
|
|
|
static ssize_t pages_to_scan_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
|
|
}
|
|
|
|
static ssize_t pages_to_scan_store(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
int err;
|
|
unsigned long nr_pages;
|
|
|
|
err = strict_strtoul(buf, 10, &nr_pages);
|
|
if (err || nr_pages > UINT_MAX)
|
|
return -EINVAL;
|
|
|
|
ksm_thread_pages_to_scan = nr_pages;
|
|
|
|
return count;
|
|
}
|
|
KSM_ATTR(pages_to_scan);
|
|
|
|
static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
|
|
char *buf)
|
|
{
|
|
return sprintf(buf, "%u\n", ksm_run);
|
|
}
|
|
|
|
static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
int err;
|
|
unsigned long flags;
|
|
|
|
err = strict_strtoul(buf, 10, &flags);
|
|
if (err || flags > UINT_MAX)
|
|
return -EINVAL;
|
|
if (flags > KSM_RUN_UNMERGE)
|
|
return -EINVAL;
|
|
|
|
/*
|
|
* KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
|
|
* KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
|
|
* breaking COW to free the unswappable pages_shared (but leaves
|
|
* mm_slots on the list for when ksmd may be set running again).
|
|
*/
|
|
|
|
mutex_lock(&ksm_thread_mutex);
|
|
if (ksm_run != flags) {
|
|
ksm_run = flags;
|
|
if (flags & KSM_RUN_UNMERGE) {
|
|
current->flags |= PF_OOM_ORIGIN;
|
|
err = unmerge_and_remove_all_rmap_items();
|
|
current->flags &= ~PF_OOM_ORIGIN;
|
|
if (err) {
|
|
ksm_run = KSM_RUN_STOP;
|
|
count = err;
|
|
}
|
|
}
|
|
}
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
if (flags & KSM_RUN_MERGE)
|
|
wake_up_interruptible(&ksm_thread_wait);
|
|
|
|
return count;
|
|
}
|
|
KSM_ATTR(run);
|
|
|
|
static ssize_t max_kernel_pages_store(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
int err;
|
|
unsigned long nr_pages;
|
|
|
|
err = strict_strtoul(buf, 10, &nr_pages);
|
|
if (err)
|
|
return -EINVAL;
|
|
|
|
ksm_max_kernel_pages = nr_pages;
|
|
|
|
return count;
|
|
}
|
|
|
|
static ssize_t max_kernel_pages_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
|
|
}
|
|
KSM_ATTR(max_kernel_pages);
|
|
|
|
static ssize_t pages_shared_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_pages_shared);
|
|
}
|
|
KSM_ATTR_RO(pages_shared);
|
|
|
|
static ssize_t pages_sharing_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_pages_sharing);
|
|
}
|
|
KSM_ATTR_RO(pages_sharing);
|
|
|
|
static ssize_t pages_unshared_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_pages_unshared);
|
|
}
|
|
KSM_ATTR_RO(pages_unshared);
|
|
|
|
static ssize_t pages_volatile_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
long ksm_pages_volatile;
|
|
|
|
ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
|
|
- ksm_pages_sharing - ksm_pages_unshared;
|
|
/*
|
|
* It was not worth any locking to calculate that statistic,
|
|
* but it might therefore sometimes be negative: conceal that.
|
|
*/
|
|
if (ksm_pages_volatile < 0)
|
|
ksm_pages_volatile = 0;
|
|
return sprintf(buf, "%ld\n", ksm_pages_volatile);
|
|
}
|
|
KSM_ATTR_RO(pages_volatile);
|
|
|
|
static ssize_t full_scans_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_scan.seqnr);
|
|
}
|
|
KSM_ATTR_RO(full_scans);
|
|
|
|
static struct attribute *ksm_attrs[] = {
|
|
&sleep_millisecs_attr.attr,
|
|
&pages_to_scan_attr.attr,
|
|
&run_attr.attr,
|
|
&max_kernel_pages_attr.attr,
|
|
&pages_shared_attr.attr,
|
|
&pages_sharing_attr.attr,
|
|
&pages_unshared_attr.attr,
|
|
&pages_volatile_attr.attr,
|
|
&full_scans_attr.attr,
|
|
NULL,
|
|
};
|
|
|
|
static struct attribute_group ksm_attr_group = {
|
|
.attrs = ksm_attrs,
|
|
.name = "ksm",
|
|
};
|
|
#endif /* CONFIG_SYSFS */
|
|
|
|
static int __init ksm_init(void)
|
|
{
|
|
struct task_struct *ksm_thread;
|
|
int err;
|
|
|
|
ksm_max_kernel_pages = totalram_pages / 4;
|
|
|
|
err = ksm_slab_init();
|
|
if (err)
|
|
goto out;
|
|
|
|
err = mm_slots_hash_init();
|
|
if (err)
|
|
goto out_free1;
|
|
|
|
ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
|
|
if (IS_ERR(ksm_thread)) {
|
|
printk(KERN_ERR "ksm: creating kthread failed\n");
|
|
err = PTR_ERR(ksm_thread);
|
|
goto out_free2;
|
|
}
|
|
|
|
#ifdef CONFIG_SYSFS
|
|
err = sysfs_create_group(mm_kobj, &ksm_attr_group);
|
|
if (err) {
|
|
printk(KERN_ERR "ksm: register sysfs failed\n");
|
|
kthread_stop(ksm_thread);
|
|
goto out_free2;
|
|
}
|
|
#else
|
|
ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
|
|
|
|
#endif /* CONFIG_SYSFS */
|
|
|
|
return 0;
|
|
|
|
out_free2:
|
|
mm_slots_hash_free();
|
|
out_free1:
|
|
ksm_slab_free();
|
|
out:
|
|
return err;
|
|
}
|
|
module_init(ksm_init)
|