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![Hugh Dickins](/assets/img/avatar_default.png)
This patch presents the mm interface to a dummy version of ksm.c, for better scrutiny of that interface: the real ksm.c follows later. When CONFIG_KSM is not set, madvise(2) reject MADV_MERGEABLE and MADV_UNMERGEABLE with EINVAL, since that seems more helpful than pretending that they can be serviced. But when CONFIG_KSM=y, accept them even if KSM is not currently running, and even on areas which KSM will not touch (e.g. hugetlb or shared file or special driver mappings). Like other madvices, report ENOMEM despite success if any area in the range is unmapped, and use EAGAIN to report out of memory. Define vma flag VM_MERGEABLE to identify an area on which KSM may try merging pages: leave it to ksm_madvise() to decide whether to set it. Define mm flag MMF_VM_MERGEABLE to identify an mm which might contain VM_MERGEABLE areas, to minimize callouts when forking or exiting. Based upon earlier patches by Chris Wright and Izik Eidus. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by: Chris Wright <chrisw@redhat.com> Signed-off-by: Izik Eidus <ieidus@redhat.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Avi Kivity <avi@redhat.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
386 lines
10 KiB
C
386 lines
10 KiB
C
/*
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* linux/mm/madvise.c
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*
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* Copyright (C) 1999 Linus Torvalds
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* Copyright (C) 2002 Christoph Hellwig
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*/
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#include <linux/mman.h>
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#include <linux/pagemap.h>
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#include <linux/syscalls.h>
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#include <linux/mempolicy.h>
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#include <linux/hugetlb.h>
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#include <linux/sched.h>
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#include <linux/ksm.h>
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/*
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* Any behaviour which results in changes to the vma->vm_flags needs to
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* take mmap_sem for writing. Others, which simply traverse vmas, need
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* to only take it for reading.
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*/
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static int madvise_need_mmap_write(int behavior)
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{
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switch (behavior) {
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case MADV_REMOVE:
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case MADV_WILLNEED:
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case MADV_DONTNEED:
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return 0;
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default:
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/* be safe, default to 1. list exceptions explicitly */
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return 1;
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}
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}
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/*
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* We can potentially split a vm area into separate
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* areas, each area with its own behavior.
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*/
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static long madvise_behavior(struct vm_area_struct * vma,
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struct vm_area_struct **prev,
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unsigned long start, unsigned long end, int behavior)
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{
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struct mm_struct * mm = vma->vm_mm;
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int error = 0;
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pgoff_t pgoff;
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unsigned long new_flags = vma->vm_flags;
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switch (behavior) {
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case MADV_NORMAL:
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new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
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break;
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case MADV_SEQUENTIAL:
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new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
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break;
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case MADV_RANDOM:
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new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
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break;
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case MADV_DONTFORK:
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new_flags |= VM_DONTCOPY;
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break;
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case MADV_DOFORK:
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if (vma->vm_flags & VM_IO) {
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error = -EINVAL;
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goto out;
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}
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new_flags &= ~VM_DONTCOPY;
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break;
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case MADV_MERGEABLE:
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case MADV_UNMERGEABLE:
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error = ksm_madvise(vma, start, end, behavior, &new_flags);
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if (error)
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goto out;
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break;
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}
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if (new_flags == vma->vm_flags) {
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*prev = vma;
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goto out;
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}
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pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
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*prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
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vma->vm_file, pgoff, vma_policy(vma));
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if (*prev) {
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vma = *prev;
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goto success;
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}
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*prev = vma;
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if (start != vma->vm_start) {
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error = split_vma(mm, vma, start, 1);
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if (error)
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goto out;
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}
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if (end != vma->vm_end) {
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error = split_vma(mm, vma, end, 0);
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if (error)
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goto out;
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}
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success:
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/*
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* vm_flags is protected by the mmap_sem held in write mode.
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*/
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vma->vm_flags = new_flags;
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out:
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if (error == -ENOMEM)
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error = -EAGAIN;
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return error;
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}
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/*
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* Schedule all required I/O operations. Do not wait for completion.
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*/
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static long madvise_willneed(struct vm_area_struct * vma,
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struct vm_area_struct ** prev,
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unsigned long start, unsigned long end)
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{
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struct file *file = vma->vm_file;
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if (!file)
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return -EBADF;
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if (file->f_mapping->a_ops->get_xip_mem) {
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/* no bad return value, but ignore advice */
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return 0;
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}
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*prev = vma;
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start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
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if (end > vma->vm_end)
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end = vma->vm_end;
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end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
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force_page_cache_readahead(file->f_mapping, file, start, end - start);
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return 0;
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}
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/*
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* Application no longer needs these pages. If the pages are dirty,
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* it's OK to just throw them away. The app will be more careful about
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* data it wants to keep. Be sure to free swap resources too. The
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* zap_page_range call sets things up for shrink_active_list to actually free
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* these pages later if no one else has touched them in the meantime,
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* although we could add these pages to a global reuse list for
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* shrink_active_list to pick up before reclaiming other pages.
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*
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* NB: This interface discards data rather than pushes it out to swap,
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* as some implementations do. This has performance implications for
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* applications like large transactional databases which want to discard
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* pages in anonymous maps after committing to backing store the data
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* that was kept in them. There is no reason to write this data out to
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* the swap area if the application is discarding it.
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*
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* An interface that causes the system to free clean pages and flush
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* dirty pages is already available as msync(MS_INVALIDATE).
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*/
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static long madvise_dontneed(struct vm_area_struct * vma,
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struct vm_area_struct ** prev,
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unsigned long start, unsigned long end)
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{
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*prev = vma;
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if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
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return -EINVAL;
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if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
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struct zap_details details = {
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.nonlinear_vma = vma,
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.last_index = ULONG_MAX,
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};
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zap_page_range(vma, start, end - start, &details);
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} else
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zap_page_range(vma, start, end - start, NULL);
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return 0;
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}
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/*
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* Application wants to free up the pages and associated backing store.
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* This is effectively punching a hole into the middle of a file.
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*
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* NOTE: Currently, only shmfs/tmpfs is supported for this operation.
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* Other filesystems return -ENOSYS.
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*/
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static long madvise_remove(struct vm_area_struct *vma,
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struct vm_area_struct **prev,
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unsigned long start, unsigned long end)
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{
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struct address_space *mapping;
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loff_t offset, endoff;
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int error;
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*prev = NULL; /* tell sys_madvise we drop mmap_sem */
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if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))
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return -EINVAL;
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if (!vma->vm_file || !vma->vm_file->f_mapping
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|| !vma->vm_file->f_mapping->host) {
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return -EINVAL;
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}
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if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
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return -EACCES;
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mapping = vma->vm_file->f_mapping;
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offset = (loff_t)(start - vma->vm_start)
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+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
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endoff = (loff_t)(end - vma->vm_start - 1)
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+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
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/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
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up_read(¤t->mm->mmap_sem);
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error = vmtruncate_range(mapping->host, offset, endoff);
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down_read(¤t->mm->mmap_sem);
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return error;
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}
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static long
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madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
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unsigned long start, unsigned long end, int behavior)
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{
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switch (behavior) {
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case MADV_REMOVE:
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return madvise_remove(vma, prev, start, end);
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case MADV_WILLNEED:
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return madvise_willneed(vma, prev, start, end);
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case MADV_DONTNEED:
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return madvise_dontneed(vma, prev, start, end);
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default:
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return madvise_behavior(vma, prev, start, end, behavior);
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}
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}
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static int
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madvise_behavior_valid(int behavior)
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{
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switch (behavior) {
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case MADV_DOFORK:
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case MADV_DONTFORK:
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case MADV_NORMAL:
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case MADV_SEQUENTIAL:
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case MADV_RANDOM:
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case MADV_REMOVE:
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case MADV_WILLNEED:
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case MADV_DONTNEED:
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#ifdef CONFIG_KSM
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case MADV_MERGEABLE:
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case MADV_UNMERGEABLE:
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#endif
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return 1;
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default:
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return 0;
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}
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}
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/*
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* The madvise(2) system call.
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*
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* Applications can use madvise() to advise the kernel how it should
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* handle paging I/O in this VM area. The idea is to help the kernel
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* use appropriate read-ahead and caching techniques. The information
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* provided is advisory only, and can be safely disregarded by the
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* kernel without affecting the correct operation of the application.
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*
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* behavior values:
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* MADV_NORMAL - the default behavior is to read clusters. This
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* results in some read-ahead and read-behind.
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* MADV_RANDOM - the system should read the minimum amount of data
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* on any access, since it is unlikely that the appli-
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* cation will need more than what it asks for.
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* MADV_SEQUENTIAL - pages in the given range will probably be accessed
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* once, so they can be aggressively read ahead, and
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* can be freed soon after they are accessed.
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* MADV_WILLNEED - the application is notifying the system to read
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* some pages ahead.
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* MADV_DONTNEED - the application is finished with the given range,
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* so the kernel can free resources associated with it.
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* MADV_REMOVE - the application wants to free up the given range of
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* pages and associated backing store.
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* MADV_DONTFORK - omit this area from child's address space when forking:
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* typically, to avoid COWing pages pinned by get_user_pages().
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* MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
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* MADV_MERGEABLE - the application recommends that KSM try to merge pages in
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* this area with pages of identical content from other such areas.
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* MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
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*
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* return values:
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* zero - success
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* -EINVAL - start + len < 0, start is not page-aligned,
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* "behavior" is not a valid value, or application
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* is attempting to release locked or shared pages.
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* -ENOMEM - addresses in the specified range are not currently
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* mapped, or are outside the AS of the process.
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* -EIO - an I/O error occurred while paging in data.
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* -EBADF - map exists, but area maps something that isn't a file.
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* -EAGAIN - a kernel resource was temporarily unavailable.
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*/
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SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
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{
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unsigned long end, tmp;
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struct vm_area_struct * vma, *prev;
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int unmapped_error = 0;
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int error = -EINVAL;
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int write;
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size_t len;
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if (!madvise_behavior_valid(behavior))
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return error;
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write = madvise_need_mmap_write(behavior);
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if (write)
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down_write(¤t->mm->mmap_sem);
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else
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down_read(¤t->mm->mmap_sem);
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if (start & ~PAGE_MASK)
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goto out;
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len = (len_in + ~PAGE_MASK) & PAGE_MASK;
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/* Check to see whether len was rounded up from small -ve to zero */
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if (len_in && !len)
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goto out;
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end = start + len;
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if (end < start)
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goto out;
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error = 0;
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if (end == start)
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goto out;
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/*
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* If the interval [start,end) covers some unmapped address
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* ranges, just ignore them, but return -ENOMEM at the end.
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* - different from the way of handling in mlock etc.
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*/
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vma = find_vma_prev(current->mm, start, &prev);
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if (vma && start > vma->vm_start)
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prev = vma;
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for (;;) {
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/* Still start < end. */
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error = -ENOMEM;
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if (!vma)
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goto out;
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/* Here start < (end|vma->vm_end). */
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if (start < vma->vm_start) {
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unmapped_error = -ENOMEM;
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start = vma->vm_start;
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if (start >= end)
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goto out;
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}
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/* Here vma->vm_start <= start < (end|vma->vm_end) */
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tmp = vma->vm_end;
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if (end < tmp)
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tmp = end;
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/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
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error = madvise_vma(vma, &prev, start, tmp, behavior);
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if (error)
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goto out;
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start = tmp;
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if (prev && start < prev->vm_end)
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start = prev->vm_end;
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error = unmapped_error;
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if (start >= end)
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goto out;
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if (prev)
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vma = prev->vm_next;
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else /* madvise_remove dropped mmap_sem */
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vma = find_vma(current->mm, start);
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}
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out:
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if (write)
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up_write(¤t->mm->mmap_sem);
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else
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up_read(¤t->mm->mmap_sem);
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return error;
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}
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