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![Vladimir Davydov](/assets/img/avatar_default.png)
To speed up further allocations SLUB may store empty slabs in per cpu/node partial lists instead of freeing them immediately. This prevents per memcg caches destruction, because kmem caches created for a memory cgroup are only destroyed after the last page charged to the cgroup is freed. To fix this issue, this patch resurrects approach first proposed in [1]. It forbids SLUB to cache empty slabs after the memory cgroup that the cache belongs to was destroyed. It is achieved by setting kmem_cache's cpu_partial and min_partial constants to 0 and tuning put_cpu_partial() so that it would drop frozen empty slabs immediately if cpu_partial = 0. The runtime overhead is minimal. From all the hot functions, we only touch relatively cold put_cpu_partial(): we make it call unfreeze_partials() after freezing a slab that belongs to an offline memory cgroup. Since slab freezing exists to avoid moving slabs from/to a partial list on free/alloc, and there can't be allocations from dead caches, it shouldn't cause any overhead. We do have to disable preemption for put_cpu_partial() to achieve that though. The original patch was accepted well and even merged to the mm tree. However, I decided to withdraw it due to changes happening to the memcg core at that time. I had an idea of introducing per-memcg shrinkers for kmem caches, but now, as memcg has finally settled down, I do not see it as an option, because SLUB shrinker would be too costly to call since SLUB does not keep free slabs on a separate list. Besides, we currently do not even call per-memcg shrinkers for offline memcgs. Overall, it would introduce much more complexity to both SLUB and memcg than this small patch. Regarding to SLAB, there's no problem with it, because it shrinks per-cpu/node caches periodically. Thanks to list_lru reparenting, we no longer keep entries for offline cgroups in per-memcg arrays (such as memcg_cache_params->memcg_caches), so we do not have to bother if a per-memcg cache will be shrunk a bit later than it could be. [1] http://thread.gmane.org/gmane.linux.kernel.mm/118649/focus=118650 Signed-off-by: Vladimir Davydov <vdavydov@parallels.com> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
642 lines
16 KiB
C
642 lines
16 KiB
C
/*
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* SLOB Allocator: Simple List Of Blocks
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*
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* Matt Mackall <mpm@selenic.com> 12/30/03
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*
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* NUMA support by Paul Mundt, 2007.
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*
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* How SLOB works:
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*
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* The core of SLOB is a traditional K&R style heap allocator, with
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* support for returning aligned objects. The granularity of this
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* allocator is as little as 2 bytes, however typically most architectures
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* will require 4 bytes on 32-bit and 8 bytes on 64-bit.
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*
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* The slob heap is a set of linked list of pages from alloc_pages(),
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* and within each page, there is a singly-linked list of free blocks
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* (slob_t). The heap is grown on demand. To reduce fragmentation,
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* heap pages are segregated into three lists, with objects less than
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* 256 bytes, objects less than 1024 bytes, and all other objects.
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*
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* Allocation from heap involves first searching for a page with
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* sufficient free blocks (using a next-fit-like approach) followed by
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* a first-fit scan of the page. Deallocation inserts objects back
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* into the free list in address order, so this is effectively an
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* address-ordered first fit.
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*
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* Above this is an implementation of kmalloc/kfree. Blocks returned
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* from kmalloc are prepended with a 4-byte header with the kmalloc size.
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* If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
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* alloc_pages() directly, allocating compound pages so the page order
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* does not have to be separately tracked.
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* These objects are detected in kfree() because PageSlab()
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* is false for them.
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*
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* SLAB is emulated on top of SLOB by simply calling constructors and
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* destructors for every SLAB allocation. Objects are returned with the
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* 4-byte alignment unless the SLAB_HWCACHE_ALIGN flag is set, in which
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* case the low-level allocator will fragment blocks to create the proper
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* alignment. Again, objects of page-size or greater are allocated by
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* calling alloc_pages(). As SLAB objects know their size, no separate
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* size bookkeeping is necessary and there is essentially no allocation
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* space overhead, and compound pages aren't needed for multi-page
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* allocations.
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*
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* NUMA support in SLOB is fairly simplistic, pushing most of the real
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* logic down to the page allocator, and simply doing the node accounting
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* on the upper levels. In the event that a node id is explicitly
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* provided, alloc_pages_exact_node() with the specified node id is used
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* instead. The common case (or when the node id isn't explicitly provided)
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* will default to the current node, as per numa_node_id().
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*
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* Node aware pages are still inserted in to the global freelist, and
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* these are scanned for by matching against the node id encoded in the
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* page flags. As a result, block allocations that can be satisfied from
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* the freelist will only be done so on pages residing on the same node,
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* in order to prevent random node placement.
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*/
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include <linux/mm.h>
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#include <linux/swap.h> /* struct reclaim_state */
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#include <linux/cache.h>
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#include <linux/init.h>
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#include <linux/export.h>
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#include <linux/rcupdate.h>
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#include <linux/list.h>
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#include <linux/kmemleak.h>
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#include <trace/events/kmem.h>
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#include <linux/atomic.h>
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#include "slab.h"
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/*
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* slob_block has a field 'units', which indicates size of block if +ve,
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* or offset of next block if -ve (in SLOB_UNITs).
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*
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* Free blocks of size 1 unit simply contain the offset of the next block.
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* Those with larger size contain their size in the first SLOB_UNIT of
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* memory, and the offset of the next free block in the second SLOB_UNIT.
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*/
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#if PAGE_SIZE <= (32767 * 2)
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typedef s16 slobidx_t;
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#else
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typedef s32 slobidx_t;
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#endif
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struct slob_block {
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slobidx_t units;
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};
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typedef struct slob_block slob_t;
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/*
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* All partially free slob pages go on these lists.
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*/
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#define SLOB_BREAK1 256
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#define SLOB_BREAK2 1024
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static LIST_HEAD(free_slob_small);
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static LIST_HEAD(free_slob_medium);
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static LIST_HEAD(free_slob_large);
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/*
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* slob_page_free: true for pages on free_slob_pages list.
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*/
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static inline int slob_page_free(struct page *sp)
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{
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return PageSlobFree(sp);
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}
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static void set_slob_page_free(struct page *sp, struct list_head *list)
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{
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list_add(&sp->lru, list);
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__SetPageSlobFree(sp);
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}
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static inline void clear_slob_page_free(struct page *sp)
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{
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list_del(&sp->lru);
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__ClearPageSlobFree(sp);
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}
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#define SLOB_UNIT sizeof(slob_t)
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#define SLOB_UNITS(size) DIV_ROUND_UP(size, SLOB_UNIT)
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/*
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* struct slob_rcu is inserted at the tail of allocated slob blocks, which
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* were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
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* the block using call_rcu.
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*/
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struct slob_rcu {
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struct rcu_head head;
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int size;
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};
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/*
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* slob_lock protects all slob allocator structures.
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*/
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static DEFINE_SPINLOCK(slob_lock);
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/*
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* Encode the given size and next info into a free slob block s.
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*/
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static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
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{
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slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
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slobidx_t offset = next - base;
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if (size > 1) {
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s[0].units = size;
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s[1].units = offset;
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} else
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s[0].units = -offset;
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}
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/*
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* Return the size of a slob block.
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*/
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static slobidx_t slob_units(slob_t *s)
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{
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if (s->units > 0)
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return s->units;
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return 1;
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}
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/*
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* Return the next free slob block pointer after this one.
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*/
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static slob_t *slob_next(slob_t *s)
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{
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slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
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slobidx_t next;
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if (s[0].units < 0)
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next = -s[0].units;
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else
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next = s[1].units;
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return base+next;
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}
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/*
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* Returns true if s is the last free block in its page.
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*/
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static int slob_last(slob_t *s)
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{
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return !((unsigned long)slob_next(s) & ~PAGE_MASK);
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}
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static void *slob_new_pages(gfp_t gfp, int order, int node)
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{
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void *page;
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#ifdef CONFIG_NUMA
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if (node != NUMA_NO_NODE)
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page = alloc_pages_exact_node(node, gfp, order);
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else
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#endif
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page = alloc_pages(gfp, order);
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if (!page)
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return NULL;
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return page_address(page);
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}
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static void slob_free_pages(void *b, int order)
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{
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if (current->reclaim_state)
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current->reclaim_state->reclaimed_slab += 1 << order;
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free_pages((unsigned long)b, order);
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}
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/*
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* Allocate a slob block within a given slob_page sp.
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*/
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static void *slob_page_alloc(struct page *sp, size_t size, int align)
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{
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slob_t *prev, *cur, *aligned = NULL;
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int delta = 0, units = SLOB_UNITS(size);
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for (prev = NULL, cur = sp->freelist; ; prev = cur, cur = slob_next(cur)) {
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slobidx_t avail = slob_units(cur);
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if (align) {
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aligned = (slob_t *)ALIGN((unsigned long)cur, align);
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delta = aligned - cur;
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}
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if (avail >= units + delta) { /* room enough? */
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slob_t *next;
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if (delta) { /* need to fragment head to align? */
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next = slob_next(cur);
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set_slob(aligned, avail - delta, next);
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set_slob(cur, delta, aligned);
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prev = cur;
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cur = aligned;
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avail = slob_units(cur);
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}
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next = slob_next(cur);
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if (avail == units) { /* exact fit? unlink. */
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if (prev)
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set_slob(prev, slob_units(prev), next);
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else
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sp->freelist = next;
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} else { /* fragment */
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if (prev)
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set_slob(prev, slob_units(prev), cur + units);
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else
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sp->freelist = cur + units;
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set_slob(cur + units, avail - units, next);
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}
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sp->units -= units;
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if (!sp->units)
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clear_slob_page_free(sp);
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return cur;
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}
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if (slob_last(cur))
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return NULL;
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}
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}
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/*
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* slob_alloc: entry point into the slob allocator.
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*/
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static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
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{
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struct page *sp;
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struct list_head *prev;
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struct list_head *slob_list;
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slob_t *b = NULL;
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unsigned long flags;
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if (size < SLOB_BREAK1)
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slob_list = &free_slob_small;
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else if (size < SLOB_BREAK2)
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slob_list = &free_slob_medium;
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else
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slob_list = &free_slob_large;
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spin_lock_irqsave(&slob_lock, flags);
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/* Iterate through each partially free page, try to find room */
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list_for_each_entry(sp, slob_list, lru) {
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#ifdef CONFIG_NUMA
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/*
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* If there's a node specification, search for a partial
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* page with a matching node id in the freelist.
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*/
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if (node != NUMA_NO_NODE && page_to_nid(sp) != node)
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continue;
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#endif
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/* Enough room on this page? */
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if (sp->units < SLOB_UNITS(size))
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continue;
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/* Attempt to alloc */
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prev = sp->lru.prev;
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b = slob_page_alloc(sp, size, align);
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if (!b)
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continue;
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/* Improve fragment distribution and reduce our average
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* search time by starting our next search here. (see
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* Knuth vol 1, sec 2.5, pg 449) */
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if (prev != slob_list->prev &&
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slob_list->next != prev->next)
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list_move_tail(slob_list, prev->next);
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break;
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}
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spin_unlock_irqrestore(&slob_lock, flags);
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/* Not enough space: must allocate a new page */
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if (!b) {
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b = slob_new_pages(gfp & ~__GFP_ZERO, 0, node);
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if (!b)
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return NULL;
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sp = virt_to_page(b);
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__SetPageSlab(sp);
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spin_lock_irqsave(&slob_lock, flags);
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sp->units = SLOB_UNITS(PAGE_SIZE);
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sp->freelist = b;
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INIT_LIST_HEAD(&sp->lru);
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set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE));
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set_slob_page_free(sp, slob_list);
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b = slob_page_alloc(sp, size, align);
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BUG_ON(!b);
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spin_unlock_irqrestore(&slob_lock, flags);
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}
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if (unlikely((gfp & __GFP_ZERO) && b))
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memset(b, 0, size);
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return b;
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}
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/*
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* slob_free: entry point into the slob allocator.
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*/
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static void slob_free(void *block, int size)
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{
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struct page *sp;
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slob_t *prev, *next, *b = (slob_t *)block;
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slobidx_t units;
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unsigned long flags;
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struct list_head *slob_list;
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if (unlikely(ZERO_OR_NULL_PTR(block)))
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return;
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BUG_ON(!size);
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sp = virt_to_page(block);
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units = SLOB_UNITS(size);
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spin_lock_irqsave(&slob_lock, flags);
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if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
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/* Go directly to page allocator. Do not pass slob allocator */
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if (slob_page_free(sp))
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clear_slob_page_free(sp);
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spin_unlock_irqrestore(&slob_lock, flags);
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__ClearPageSlab(sp);
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page_mapcount_reset(sp);
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slob_free_pages(b, 0);
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return;
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}
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if (!slob_page_free(sp)) {
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/* This slob page is about to become partially free. Easy! */
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sp->units = units;
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sp->freelist = b;
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set_slob(b, units,
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(void *)((unsigned long)(b +
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SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));
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if (size < SLOB_BREAK1)
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slob_list = &free_slob_small;
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else if (size < SLOB_BREAK2)
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slob_list = &free_slob_medium;
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else
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slob_list = &free_slob_large;
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set_slob_page_free(sp, slob_list);
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goto out;
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}
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/*
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* Otherwise the page is already partially free, so find reinsertion
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* point.
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*/
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sp->units += units;
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if (b < (slob_t *)sp->freelist) {
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if (b + units == sp->freelist) {
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units += slob_units(sp->freelist);
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sp->freelist = slob_next(sp->freelist);
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}
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set_slob(b, units, sp->freelist);
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sp->freelist = b;
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} else {
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prev = sp->freelist;
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next = slob_next(prev);
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while (b > next) {
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prev = next;
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next = slob_next(prev);
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}
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if (!slob_last(prev) && b + units == next) {
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units += slob_units(next);
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set_slob(b, units, slob_next(next));
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} else
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set_slob(b, units, next);
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if (prev + slob_units(prev) == b) {
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units = slob_units(b) + slob_units(prev);
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set_slob(prev, units, slob_next(b));
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} else
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set_slob(prev, slob_units(prev), b);
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}
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out:
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spin_unlock_irqrestore(&slob_lock, flags);
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}
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/*
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* End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
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*/
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static __always_inline void *
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__do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
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{
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unsigned int *m;
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int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
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void *ret;
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gfp &= gfp_allowed_mask;
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lockdep_trace_alloc(gfp);
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if (size < PAGE_SIZE - align) {
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if (!size)
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return ZERO_SIZE_PTR;
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m = slob_alloc(size + align, gfp, align, node);
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if (!m)
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return NULL;
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*m = size;
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ret = (void *)m + align;
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trace_kmalloc_node(caller, ret,
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size, size + align, gfp, node);
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} else {
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unsigned int order = get_order(size);
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if (likely(order))
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gfp |= __GFP_COMP;
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ret = slob_new_pages(gfp, order, node);
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trace_kmalloc_node(caller, ret,
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size, PAGE_SIZE << order, gfp, node);
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}
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kmemleak_alloc(ret, size, 1, gfp);
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return ret;
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}
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void *__kmalloc(size_t size, gfp_t gfp)
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{
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return __do_kmalloc_node(size, gfp, NUMA_NO_NODE, _RET_IP_);
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}
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EXPORT_SYMBOL(__kmalloc);
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void *__kmalloc_track_caller(size_t size, gfp_t gfp, unsigned long caller)
|
|
{
|
|
return __do_kmalloc_node(size, gfp, NUMA_NO_NODE, caller);
|
|
}
|
|
|
|
#ifdef CONFIG_NUMA
|
|
void *__kmalloc_node_track_caller(size_t size, gfp_t gfp,
|
|
int node, unsigned long caller)
|
|
{
|
|
return __do_kmalloc_node(size, gfp, node, caller);
|
|
}
|
|
#endif
|
|
|
|
void kfree(const void *block)
|
|
{
|
|
struct page *sp;
|
|
|
|
trace_kfree(_RET_IP_, block);
|
|
|
|
if (unlikely(ZERO_OR_NULL_PTR(block)))
|
|
return;
|
|
kmemleak_free(block);
|
|
|
|
sp = virt_to_page(block);
|
|
if (PageSlab(sp)) {
|
|
int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
|
|
unsigned int *m = (unsigned int *)(block - align);
|
|
slob_free(m, *m + align);
|
|
} else
|
|
__free_pages(sp, compound_order(sp));
|
|
}
|
|
EXPORT_SYMBOL(kfree);
|
|
|
|
/* can't use ksize for kmem_cache_alloc memory, only kmalloc */
|
|
size_t ksize(const void *block)
|
|
{
|
|
struct page *sp;
|
|
int align;
|
|
unsigned int *m;
|
|
|
|
BUG_ON(!block);
|
|
if (unlikely(block == ZERO_SIZE_PTR))
|
|
return 0;
|
|
|
|
sp = virt_to_page(block);
|
|
if (unlikely(!PageSlab(sp)))
|
|
return PAGE_SIZE << compound_order(sp);
|
|
|
|
align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
|
|
m = (unsigned int *)(block - align);
|
|
return SLOB_UNITS(*m) * SLOB_UNIT;
|
|
}
|
|
EXPORT_SYMBOL(ksize);
|
|
|
|
int __kmem_cache_create(struct kmem_cache *c, unsigned long flags)
|
|
{
|
|
if (flags & SLAB_DESTROY_BY_RCU) {
|
|
/* leave room for rcu footer at the end of object */
|
|
c->size += sizeof(struct slob_rcu);
|
|
}
|
|
c->flags = flags;
|
|
return 0;
|
|
}
|
|
|
|
void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
|
|
{
|
|
void *b;
|
|
|
|
flags &= gfp_allowed_mask;
|
|
|
|
lockdep_trace_alloc(flags);
|
|
|
|
if (c->size < PAGE_SIZE) {
|
|
b = slob_alloc(c->size, flags, c->align, node);
|
|
trace_kmem_cache_alloc_node(_RET_IP_, b, c->object_size,
|
|
SLOB_UNITS(c->size) * SLOB_UNIT,
|
|
flags, node);
|
|
} else {
|
|
b = slob_new_pages(flags, get_order(c->size), node);
|
|
trace_kmem_cache_alloc_node(_RET_IP_, b, c->object_size,
|
|
PAGE_SIZE << get_order(c->size),
|
|
flags, node);
|
|
}
|
|
|
|
if (b && c->ctor)
|
|
c->ctor(b);
|
|
|
|
kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);
|
|
return b;
|
|
}
|
|
EXPORT_SYMBOL(slob_alloc_node);
|
|
|
|
void *kmem_cache_alloc(struct kmem_cache *cachep, gfp_t flags)
|
|
{
|
|
return slob_alloc_node(cachep, flags, NUMA_NO_NODE);
|
|
}
|
|
EXPORT_SYMBOL(kmem_cache_alloc);
|
|
|
|
#ifdef CONFIG_NUMA
|
|
void *__kmalloc_node(size_t size, gfp_t gfp, int node)
|
|
{
|
|
return __do_kmalloc_node(size, gfp, node, _RET_IP_);
|
|
}
|
|
EXPORT_SYMBOL(__kmalloc_node);
|
|
|
|
void *kmem_cache_alloc_node(struct kmem_cache *cachep, gfp_t gfp, int node)
|
|
{
|
|
return slob_alloc_node(cachep, gfp, node);
|
|
}
|
|
EXPORT_SYMBOL(kmem_cache_alloc_node);
|
|
#endif
|
|
|
|
static void __kmem_cache_free(void *b, int size)
|
|
{
|
|
if (size < PAGE_SIZE)
|
|
slob_free(b, size);
|
|
else
|
|
slob_free_pages(b, get_order(size));
|
|
}
|
|
|
|
static void kmem_rcu_free(struct rcu_head *head)
|
|
{
|
|
struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
|
|
void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
|
|
|
|
__kmem_cache_free(b, slob_rcu->size);
|
|
}
|
|
|
|
void kmem_cache_free(struct kmem_cache *c, void *b)
|
|
{
|
|
kmemleak_free_recursive(b, c->flags);
|
|
if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
|
|
struct slob_rcu *slob_rcu;
|
|
slob_rcu = b + (c->size - sizeof(struct slob_rcu));
|
|
slob_rcu->size = c->size;
|
|
call_rcu(&slob_rcu->head, kmem_rcu_free);
|
|
} else {
|
|
__kmem_cache_free(b, c->size);
|
|
}
|
|
|
|
trace_kmem_cache_free(_RET_IP_, b);
|
|
}
|
|
EXPORT_SYMBOL(kmem_cache_free);
|
|
|
|
int __kmem_cache_shutdown(struct kmem_cache *c)
|
|
{
|
|
/* No way to check for remaining objects */
|
|
return 0;
|
|
}
|
|
|
|
int __kmem_cache_shrink(struct kmem_cache *d, bool deactivate)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
struct kmem_cache kmem_cache_boot = {
|
|
.name = "kmem_cache",
|
|
.size = sizeof(struct kmem_cache),
|
|
.flags = SLAB_PANIC,
|
|
.align = ARCH_KMALLOC_MINALIGN,
|
|
};
|
|
|
|
void __init kmem_cache_init(void)
|
|
{
|
|
kmem_cache = &kmem_cache_boot;
|
|
slab_state = UP;
|
|
}
|
|
|
|
void __init kmem_cache_init_late(void)
|
|
{
|
|
slab_state = FULL;
|
|
}
|