slab.c 110 KB
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/*
 * linux/mm/slab.c
 * Written by Mark Hemment, 1996/97.
 * (markhe@nextd.demon.co.uk)
 *
 * kmem_cache_destroy() + some cleanup - 1999 Andrea Arcangeli
 *
 * Major cleanup, different bufctl logic, per-cpu arrays
 *	(c) 2000 Manfred Spraul
 *
 * Cleanup, make the head arrays unconditional, preparation for NUMA
 * 	(c) 2002 Manfred Spraul
 *
 * An implementation of the Slab Allocator as described in outline in;
 *	UNIX Internals: The New Frontiers by Uresh Vahalia
 *	Pub: Prentice Hall	ISBN 0-13-101908-2
 * or with a little more detail in;
 *	The Slab Allocator: An Object-Caching Kernel Memory Allocator
 *	Jeff Bonwick (Sun Microsystems).
 *	Presented at: USENIX Summer 1994 Technical Conference
 *
 * The memory is organized in caches, one cache for each object type.
 * (e.g. inode_cache, dentry_cache, buffer_head, vm_area_struct)
 * Each cache consists out of many slabs (they are small (usually one
 * page long) and always contiguous), and each slab contains multiple
 * initialized objects.
 *
 * This means, that your constructor is used only for newly allocated
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 * slabs and you must pass objects with the same initializations to
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 * kmem_cache_free.
 *
 * Each cache can only support one memory type (GFP_DMA, GFP_HIGHMEM,
 * normal). If you need a special memory type, then must create a new
 * cache for that memory type.
 *
 * In order to reduce fragmentation, the slabs are sorted in 3 groups:
 *   full slabs with 0 free objects
 *   partial slabs
 *   empty slabs with no allocated objects
 *
 * If partial slabs exist, then new allocations come from these slabs,
 * otherwise from empty slabs or new slabs are allocated.
 *
 * kmem_cache_destroy() CAN CRASH if you try to allocate from the cache
 * during kmem_cache_destroy(). The caller must prevent concurrent allocs.
 *
 * Each cache has a short per-cpu head array, most allocs
 * and frees go into that array, and if that array overflows, then 1/2
 * of the entries in the array are given back into the global cache.
 * The head array is strictly LIFO and should improve the cache hit rates.
 * On SMP, it additionally reduces the spinlock operations.
 *
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 * The c_cpuarray may not be read with enabled local interrupts -
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 * it's changed with a smp_call_function().
 *
 * SMP synchronization:
 *  constructors and destructors are called without any locking.
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 *  Several members in struct kmem_cache and struct slab never change, they
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 *	are accessed without any locking.
 *  The per-cpu arrays are never accessed from the wrong cpu, no locking,
 *  	and local interrupts are disabled so slab code is preempt-safe.
 *  The non-constant members are protected with a per-cache irq spinlock.
 *
 * Many thanks to Mark Hemment, who wrote another per-cpu slab patch
 * in 2000 - many ideas in the current implementation are derived from
 * his patch.
 *
 * Further notes from the original documentation:
 *
 * 11 April '97.  Started multi-threading - markhe
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 *	The global cache-chain is protected by the mutex 'slab_mutex'.
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 *	The sem is only needed when accessing/extending the cache-chain, which
 *	can never happen inside an interrupt (kmem_cache_create(),
 *	kmem_cache_shrink() and kmem_cache_reap()).
 *
 *	At present, each engine can be growing a cache.  This should be blocked.
 *
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 * 15 March 2005. NUMA slab allocator.
 *	Shai Fultheim <shai@scalex86.org>.
 *	Shobhit Dayal <shobhit@calsoftinc.com>
 *	Alok N Kataria <alokk@calsoftinc.com>
 *	Christoph Lameter <christoph@lameter.com>
 *
 *	Modified the slab allocator to be node aware on NUMA systems.
 *	Each node has its own list of partial, free and full slabs.
 *	All object allocations for a node occur from node specific slab lists.
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 */

#include	<linux/slab.h>
#include	<linux/mm.h>
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#include	<linux/poison.h>
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#include	<linux/swap.h>
#include	<linux/cache.h>
#include	<linux/interrupt.h>
#include	<linux/init.h>
#include	<linux/compiler.h>
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#include	<linux/cpuset.h>
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#include	<linux/proc_fs.h>
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#include	<linux/seq_file.h>
#include	<linux/notifier.h>
#include	<linux/kallsyms.h>
#include	<linux/cpu.h>
#include	<linux/sysctl.h>
#include	<linux/module.h>
#include	<linux/rcupdate.h>
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#include	<linux/string.h>
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#include	<linux/uaccess.h>
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#include	<linux/nodemask.h>
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#include	<linux/kmemleak.h>
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#include	<linux/mempolicy.h>
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#include	<linux/mutex.h>
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#include	<linux/fault-inject.h>
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#include	<linux/rtmutex.h>
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#include	<linux/reciprocal_div.h>
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#include	<linux/debugobjects.h>
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#include	<linux/kmemcheck.h>
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#include	<linux/memory.h>
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#include	<linux/prefetch.h>
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#include	<net/sock.h>

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#include	<asm/cacheflush.h>
#include	<asm/tlbflush.h>
#include	<asm/page.h>

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#include <trace/events/kmem.h>

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#include	"internal.h"

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#include	"slab.h"

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/*
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 * DEBUG	- 1 for kmem_cache_create() to honour; SLAB_RED_ZONE & SLAB_POISON.
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 *		  0 for faster, smaller code (especially in the critical paths).
 *
 * STATS	- 1 to collect stats for /proc/slabinfo.
 *		  0 for faster, smaller code (especially in the critical paths).
 *
 * FORCED_DEBUG	- 1 enables SLAB_RED_ZONE and SLAB_POISON (if possible)
 */

#ifdef CONFIG_DEBUG_SLAB
#define	DEBUG		1
#define	STATS		1
#define	FORCED_DEBUG	1
#else
#define	DEBUG		0
#define	STATS		0
#define	FORCED_DEBUG	0
#endif

/* Shouldn't this be in a header file somewhere? */
#define	BYTES_PER_WORD		sizeof(void *)
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#define	REDZONE_ALIGN		max(BYTES_PER_WORD, __alignof__(unsigned long long))
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#ifndef ARCH_KMALLOC_FLAGS
#define ARCH_KMALLOC_FLAGS SLAB_HWCACHE_ALIGN
#endif

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/*
 * true if a page was allocated from pfmemalloc reserves for network-based
 * swap
 */
static bool pfmemalloc_active __read_mostly;

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/*
 * struct array_cache
 *
 * Purpose:
 * - LIFO ordering, to hand out cache-warm objects from _alloc
 * - reduce the number of linked list operations
 * - reduce spinlock operations
 *
 * The limit is stored in the per-cpu structure to reduce the data cache
 * footprint.
 *
 */
struct array_cache {
	unsigned int avail;
	unsigned int limit;
	unsigned int batchcount;
	unsigned int touched;
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	spinlock_t lock;
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	void *entry[];	/*
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			 * Must have this definition in here for the proper
			 * alignment of array_cache. Also simplifies accessing
			 * the entries.
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			 *
			 * Entries should not be directly dereferenced as
			 * entries belonging to slabs marked pfmemalloc will
			 * have the lower bits set SLAB_OBJ_PFMEMALLOC
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			 */
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};

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#define SLAB_OBJ_PFMEMALLOC	1
static inline bool is_obj_pfmemalloc(void *objp)
{
	return (unsigned long)objp & SLAB_OBJ_PFMEMALLOC;
}

static inline void set_obj_pfmemalloc(void **objp)
{
	*objp = (void *)((unsigned long)*objp | SLAB_OBJ_PFMEMALLOC);
	return;
}

static inline void clear_obj_pfmemalloc(void **objp)
{
	*objp = (void *)((unsigned long)*objp & ~SLAB_OBJ_PFMEMALLOC);
}

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/*
 * bootstrap: The caches do not work without cpuarrays anymore, but the
 * cpuarrays are allocated from the generic caches...
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 */
#define BOOT_CPUCACHE_ENTRIES	1
struct arraycache_init {
	struct array_cache cache;
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	void *entries[BOOT_CPUCACHE_ENTRIES];
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};

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/*
 * Need this for bootstrapping a per node allocator.
 */
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#define NUM_INIT_LISTS (3 * MAX_NUMNODES)
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static struct kmem_cache_node __initdata init_kmem_cache_node[NUM_INIT_LISTS];
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#define	CACHE_CACHE 0
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#define	SIZE_AC MAX_NUMNODES
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#define	SIZE_NODE (2 * MAX_NUMNODES)
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static int drain_freelist(struct kmem_cache *cache,
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			struct kmem_cache_node *n, int tofree);
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static void free_block(struct kmem_cache *cachep, void **objpp, int len,
			int node);
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static int enable_cpucache(struct kmem_cache *cachep, gfp_t gfp);
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static void cache_reap(struct work_struct *unused);
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static int slab_early_init = 1;

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#define INDEX_AC kmalloc_index(sizeof(struct arraycache_init))
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#define INDEX_NODE kmalloc_index(sizeof(struct kmem_cache_node))
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static void kmem_cache_node_init(struct kmem_cache_node *parent)
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{
	INIT_LIST_HEAD(&parent->slabs_full);
	INIT_LIST_HEAD(&parent->slabs_partial);
	INIT_LIST_HEAD(&parent->slabs_free);
	parent->shared = NULL;
	parent->alien = NULL;
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	parent->colour_next = 0;
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	spin_lock_init(&parent->list_lock);
	parent->free_objects = 0;
	parent->free_touched = 0;
}

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#define MAKE_LIST(cachep, listp, slab, nodeid)				\
	do {								\
		INIT_LIST_HEAD(listp);					\
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		list_splice(&(cachep->node[nodeid]->slab), listp);	\
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	} while (0)

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#define	MAKE_ALL_LISTS(cachep, ptr, nodeid)				\
	do {								\
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	MAKE_LIST((cachep), (&(ptr)->slabs_full), slabs_full, nodeid);	\
	MAKE_LIST((cachep), (&(ptr)->slabs_partial), slabs_partial, nodeid); \
	MAKE_LIST((cachep), (&(ptr)->slabs_free), slabs_free, nodeid);	\
	} while (0)
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#define CFLGS_OFF_SLAB		(0x80000000UL)
#define	OFF_SLAB(x)	((x)->flags & CFLGS_OFF_SLAB)

#define BATCHREFILL_LIMIT	16
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/*
 * Optimization question: fewer reaps means less probability for unnessary
 * cpucache drain/refill cycles.
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 *
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 * OTOH the cpuarrays can contain lots of objects,
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 * which could lock up otherwise freeable slabs.
 */
#define REAPTIMEOUT_CPUC	(2*HZ)
#define REAPTIMEOUT_LIST3	(4*HZ)

#if STATS
#define	STATS_INC_ACTIVE(x)	((x)->num_active++)
#define	STATS_DEC_ACTIVE(x)	((x)->num_active--)
#define	STATS_INC_ALLOCED(x)	((x)->num_allocations++)
#define	STATS_INC_GROWN(x)	((x)->grown++)
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#define	STATS_ADD_REAPED(x,y)	((x)->reaped += (y))
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#define	STATS_SET_HIGH(x)						\
	do {								\
		if ((x)->num_active > (x)->high_mark)			\
			(x)->high_mark = (x)->num_active;		\
	} while (0)
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#define	STATS_INC_ERR(x)	((x)->errors++)
#define	STATS_INC_NODEALLOCS(x)	((x)->node_allocs++)
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#define	STATS_INC_NODEFREES(x)	((x)->node_frees++)
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#define STATS_INC_ACOVERFLOW(x)   ((x)->node_overflow++)
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#define	STATS_SET_FREEABLE(x, i)					\
	do {								\
		if ((x)->max_freeable < i)				\
			(x)->max_freeable = i;				\
	} while (0)
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#define STATS_INC_ALLOCHIT(x)	atomic_inc(&(x)->allochit)
#define STATS_INC_ALLOCMISS(x)	atomic_inc(&(x)->allocmiss)
#define STATS_INC_FREEHIT(x)	atomic_inc(&(x)->freehit)
#define STATS_INC_FREEMISS(x)	atomic_inc(&(x)->freemiss)
#else
#define	STATS_INC_ACTIVE(x)	do { } while (0)
#define	STATS_DEC_ACTIVE(x)	do { } while (0)
#define	STATS_INC_ALLOCED(x)	do { } while (0)
#define	STATS_INC_GROWN(x)	do { } while (0)
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#define	STATS_ADD_REAPED(x,y)	do { (void)(y); } while (0)
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#define	STATS_SET_HIGH(x)	do { } while (0)
#define	STATS_INC_ERR(x)	do { } while (0)
#define	STATS_INC_NODEALLOCS(x)	do { } while (0)
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#define	STATS_INC_NODEFREES(x)	do { } while (0)
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#define STATS_INC_ACOVERFLOW(x)   do { } while (0)
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#define	STATS_SET_FREEABLE(x, i) do { } while (0)
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#define STATS_INC_ALLOCHIT(x)	do { } while (0)
#define STATS_INC_ALLOCMISS(x)	do { } while (0)
#define STATS_INC_FREEHIT(x)	do { } while (0)
#define STATS_INC_FREEMISS(x)	do { } while (0)
#endif

#if DEBUG

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/*
 * memory layout of objects:
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 * 0		: objp
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 * 0 .. cachep->obj_offset - BYTES_PER_WORD - 1: padding. This ensures that
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 * 		the end of an object is aligned with the end of the real
 * 		allocation. Catches writes behind the end of the allocation.
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 * cachep->obj_offset - BYTES_PER_WORD .. cachep->obj_offset - 1:
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 * 		redzone word.
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 * cachep->obj_offset: The real object.
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 * cachep->size - 2* BYTES_PER_WORD: redzone word [BYTES_PER_WORD long]
 * cachep->size - 1* BYTES_PER_WORD: last caller address
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 *					[BYTES_PER_WORD long]
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 */
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static int obj_offset(struct kmem_cache *cachep)
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{
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	return cachep->obj_offset;
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}

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static unsigned long long *dbg_redzone1(struct kmem_cache *cachep, void *objp)
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{
	BUG_ON(!(cachep->flags & SLAB_RED_ZONE));
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	return (unsigned long long*) (objp + obj_offset(cachep) -
				      sizeof(unsigned long long));
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}

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static unsigned long long *dbg_redzone2(struct kmem_cache *cachep, void *objp)
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{
	BUG_ON(!(cachep->flags & SLAB_RED_ZONE));
	if (cachep->flags & SLAB_STORE_USER)
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		return (unsigned long long *)(objp + cachep->size -
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					      sizeof(unsigned long long) -
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					      REDZONE_ALIGN);
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	return (unsigned long long *) (objp + cachep->size -
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				       sizeof(unsigned long long));
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}

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static void **dbg_userword(struct kmem_cache *cachep, void *objp)
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{
	BUG_ON(!(cachep->flags & SLAB_STORE_USER));
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	return (void **)(objp + cachep->size - BYTES_PER_WORD);
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}

#else

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#define obj_offset(x)			0
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#define dbg_redzone1(cachep, objp)	({BUG(); (unsigned long long *)NULL;})
#define dbg_redzone2(cachep, objp)	({BUG(); (unsigned long long *)NULL;})
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#define dbg_userword(cachep, objp)	({BUG(); (void **)NULL;})

#endif

/*
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 * Do not go above this order unless 0 objects fit into the slab or
 * overridden on the command line.
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 */
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#define	SLAB_MAX_ORDER_HI	1
#define	SLAB_MAX_ORDER_LO	0
static int slab_max_order = SLAB_MAX_ORDER_LO;
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static bool slab_max_order_set __initdata;
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static inline struct kmem_cache *virt_to_cache(const void *obj)
{
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	struct page *page = virt_to_head_page(obj);
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	return page->slab_cache;
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}

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static inline void *index_to_obj(struct kmem_cache *cache, struct page *page,
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				 unsigned int idx)
{
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	return page->s_mem + cache->size * idx;
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}

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/*
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 * We want to avoid an expensive divide : (offset / cache->size)
 *   Using the fact that size is a constant for a particular cache,
 *   we can replace (offset / cache->size) by
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 *   reciprocal_divide(offset, cache->reciprocal_buffer_size)
 */
static inline unsigned int obj_to_index(const struct kmem_cache *cache,
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					const struct page *page, void *obj)
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{
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	u32 offset = (obj - page->s_mem);
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	return reciprocal_divide(offset, cache->reciprocal_buffer_size);
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}

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static struct arraycache_init initarray_generic =
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    { {0, BOOT_CPUCACHE_ENTRIES, 1, 0} };
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/* internal cache of cache description objs */
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static struct kmem_cache kmem_cache_boot = {
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	.batchcount = 1,
	.limit = BOOT_CPUCACHE_ENTRIES,
	.shared = 1,
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	.size = sizeof(struct kmem_cache),
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	.name = "kmem_cache",
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};

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#define BAD_ALIEN_MAGIC 0x01020304ul

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#ifdef CONFIG_LOCKDEP

/*
 * Slab sometimes uses the kmalloc slabs to store the slab headers
 * for other slabs "off slab".
 * The locking for this is tricky in that it nests within the locks
 * of all other slabs in a few places; to deal with this special
 * locking we put on-slab caches into a separate lock-class.
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 *
 * We set lock class for alien array caches which are up during init.
 * The lock annotation will be lost if all cpus of a node goes down and
 * then comes back up during hotplug
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 */
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static struct lock_class_key on_slab_l3_key;
static struct lock_class_key on_slab_alc_key;

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static struct lock_class_key debugobj_l3_key;
static struct lock_class_key debugobj_alc_key;

static void slab_set_lock_classes(struct kmem_cache *cachep,
		struct lock_class_key *l3_key, struct lock_class_key *alc_key,
		int q)
{
	struct array_cache **alc;
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	struct kmem_cache_node *n;
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	int r;

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	n = cachep->node[q];
	if (!n)
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		return;

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	lockdep_set_class(&n->list_lock, l3_key);
	alc = n->alien;
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	/*
	 * FIXME: This check for BAD_ALIEN_MAGIC
	 * should go away when common slab code is taught to
	 * work even without alien caches.
	 * Currently, non NUMA code returns BAD_ALIEN_MAGIC
	 * for alloc_alien_cache,
	 */
	if (!alc || (unsigned long)alc == BAD_ALIEN_MAGIC)
		return;
	for_each_node(r) {
		if (alc[r])
			lockdep_set_class(&alc[r]->lock, alc_key);
	}
}

static void slab_set_debugobj_lock_classes_node(struct kmem_cache *cachep, int node)
{
	slab_set_lock_classes(cachep, &debugobj_l3_key, &debugobj_alc_key, node);
}

static void slab_set_debugobj_lock_classes(struct kmem_cache *cachep)
{
	int node;

	for_each_online_node(node)
		slab_set_debugobj_lock_classes_node(cachep, node);
}

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static void init_node_lock_keys(int q)
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{
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	int i;
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	if (slab_state < UP)
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		return;

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	for (i = 1; i <= KMALLOC_SHIFT_HIGH; i++) {
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		struct kmem_cache_node *n;
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		struct kmem_cache *cache = kmalloc_caches[i];

		if (!cache)
			continue;
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		n = cache->node[q];
		if (!n || OFF_SLAB(cache))
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			continue;
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		slab_set_lock_classes(cache, &on_slab_l3_key,
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				&on_slab_alc_key, q);
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	}
}
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static void on_slab_lock_classes_node(struct kmem_cache *cachep, int q)
{
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	if (!cachep->node[q])
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		return;

	slab_set_lock_classes(cachep, &on_slab_l3_key,
			&on_slab_alc_key, q);
}

static inline void on_slab_lock_classes(struct kmem_cache *cachep)
{
	int node;

	VM_BUG_ON(OFF_SLAB(cachep));
	for_each_node(node)
		on_slab_lock_classes_node(cachep, node);
}

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static inline void init_lock_keys(void)
{
	int node;

	for_each_node(node)
		init_node_lock_keys(node);
}
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#else
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static void init_node_lock_keys(int q)
{
}

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static inline void init_lock_keys(void)
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{
}
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static inline void on_slab_lock_classes(struct kmem_cache *cachep)
{
}

static inline void on_slab_lock_classes_node(struct kmem_cache *cachep, int node)
{
}

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static void slab_set_debugobj_lock_classes_node(struct kmem_cache *cachep, int node)
{
}

static void slab_set_debugobj_lock_classes(struct kmem_cache *cachep)
{
}
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#endif

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static DEFINE_PER_CPU(struct delayed_work, slab_reap_work);
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static inline struct array_cache *cpu_cache_get(struct kmem_cache *cachep)
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{
	return cachep->array[smp_processor_id()];
}

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static size_t slab_mgmt_size(size_t nr_objs, size_t align)
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{
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	return ALIGN(nr_objs * sizeof(unsigned int), align);
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}
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/*
 * Calculate the number of objects and left-over bytes for a given buffer size.
 */
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static void cache_estimate(unsigned long gfporder, size_t buffer_size,
			   size_t align, int flags, size_t *left_over,
			   unsigned int *num)
{
	int nr_objs;
	size_t mgmt_size;
	size_t slab_size = PAGE_SIZE << gfporder;
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	/*
	 * The slab management structure can be either off the slab or
	 * on it. For the latter case, the memory allocated for a
	 * slab is used for:
	 *
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	 * - One unsigned int for each object
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	 * - Padding to respect alignment of @align
	 * - @buffer_size bytes for each object
	 *
	 * If the slab management structure is off the slab, then the
	 * alignment will already be calculated into the size. Because
	 * the slabs are all pages aligned, the objects will be at the
	 * correct alignment when allocated.
	 */
	if (flags & CFLGS_OFF_SLAB) {
		mgmt_size = 0;
		nr_objs = slab_size / buffer_size;

	} else {
		/*
		 * Ignore padding for the initial guess. The padding
		 * is at most @align-1 bytes, and @buffer_size is at
		 * least @align. In the worst case, this result will
		 * be one greater than the number of objects that fit
		 * into the memory allocation when taking the padding
		 * into account.
		 */
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		nr_objs = (slab_size) / (buffer_size + sizeof(unsigned int));
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		/*
		 * This calculated number will be either the right
		 * amount, or one greater than what we want.
		 */
		if (slab_mgmt_size(nr_objs, align) + nr_objs*buffer_size
		       > slab_size)
			nr_objs--;

		mgmt_size = slab_mgmt_size(nr_objs, align);
	}
	*num = nr_objs;
	*left_over = slab_size - nr_objs*buffer_size - mgmt_size;
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}

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#if DEBUG
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#define slab_error(cachep, msg) __slab_error(__func__, cachep, msg)
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static void __slab_error(const char *function, struct kmem_cache *cachep,
			char *msg)
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{
	printk(KERN_ERR "slab error in %s(): cache `%s': %s\n",
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	       function, cachep->name, msg);
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	dump_stack();
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	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
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}
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#endif
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/*
 * By default on NUMA we use alien caches to stage the freeing of
 * objects allocated from other nodes. This causes massive memory
 * inefficiencies when using fake NUMA setup to split memory into a
 * large number of small nodes, so it can be disabled on the command
 * line
  */

static int use_alien_caches __read_mostly = 1;
static int __init noaliencache_setup(char *s)
{
	use_alien_caches = 0;
	return 1;
}
__setup("noaliencache", noaliencache_setup);

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static int __init slab_max_order_setup(char *str)
{
	get_option(&str, &slab_max_order);
	slab_max_order = slab_max_order < 0 ? 0 :
				min(slab_max_order, MAX_ORDER - 1);
	slab_max_order_set = true;

	return 1;
}
__setup("slab_max_order=", slab_max_order_setup);

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#ifdef CONFIG_NUMA
/*
 * Special reaping functions for NUMA systems called from cache_reap().
 * These take care of doing round robin flushing of alien caches (containing
 * objects freed on different nodes from which they were allocated) and the
 * flushing of remote pcps by calling drain_node_pages.
 */
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static DEFINE_PER_CPU(unsigned long, slab_reap_node);
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static void init_reap_node(int cpu)
{
	int node;

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	node = next_node(cpu_to_mem(cpu), node_online_map);
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	if (node == MAX_NUMNODES)
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		node = first_node(node_online_map);
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	per_cpu(slab_reap_node, cpu) = node;
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}

static void next_reap_node(void)
{
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	int node = __this_cpu_read(slab_reap_node);
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	node = next_node(node, node_online_map);
	if (unlikely(node >= MAX_NUMNODES))
		node = first_node(node_online_map);
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	__this_cpu_write(slab_reap_node, node);
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}

#else
#define init_reap_node(cpu) do { } while (0)
#define next_reap_node(void) do { } while (0)
#endif

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/*
 * Initiate the reap timer running on the target CPU.  We run at around 1 to 2Hz
 * via the workqueue/eventd.
 * Add the CPU number into the expiration time to minimize the possibility of
 * the CPUs getting into lockstep and contending for the global cache chain
 * lock.
 */
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static void start_cpu_timer(int cpu)
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{
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	struct delayed_work *reap_work = &per_cpu(slab_reap_work, cpu);
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	/*
	 * When this gets called from do_initcalls via cpucache_init(),
	 * init_workqueues() has already run, so keventd will be setup
	 * at that time.
	 */
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	if (keventd_up() && reap_work->work.func == NULL) {
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		init_reap_node(cpu);
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		INIT_DEFERRABLE_WORK(reap_work, cache_reap);
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		schedule_delayed_work_on(cpu, reap_work,
					__round_jiffies_relative(HZ, cpu));
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	}
}

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static struct array_cache *alloc_arraycache(int node, int entries,
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					    int batchcount, gfp_t gfp)
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{
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	int memsize = sizeof(void *) * entries + sizeof(struct array_cache);
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	struct array_cache *nc = NULL;

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	nc = kmalloc_node(memsize, gfp, node);
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	/*
	 * The array_cache structures contain pointers to free object.
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	 * However, when such objects are allocated or transferred to another
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	 * cache the pointers are not cleared and they could be counted as
	 * valid references during a kmemleak scan. Therefore, kmemleak must
	 * not scan such objects.
	 */
	kmemleak_no_scan(nc);
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	if (nc) {
		nc->avail = 0;
		nc->limit = entries;
		nc->batchcount = batchcount;
		nc->touched = 0;
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		spin_lock_init(&nc->lock);
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	}
	return nc;
}

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static inline bool is_slab_pfmemalloc(struct page *page)
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{
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	struct page *mem_page = virt_to_page(page->s_mem);
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	return PageSlabPfmemalloc(mem_page);
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}

/* Clears pfmemalloc_active if no slabs have pfmalloc set */
static void recheck_pfmemalloc_active(struct kmem_cache *cachep,
						struct array_cache *ac)
{
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	struct kmem_cache_node *n = cachep->node[numa_mem_id()];
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	struct page *page;
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	unsigned long flags;

	if (!pfmemalloc_active)
		return;

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	spin_lock_irqsave(&n->list_lock, flags);
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	list_for_each_entry(page, &n->slabs_full, lru)
		if (is_slab_pfmemalloc(page))
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			goto out;

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	list_for_each_entry(page, &n->slabs_partial, lru)
		if (is_slab_pfmemalloc(page))
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			goto out;

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	list_for_each_entry(page, &n->slabs_free, lru)
		if (is_slab_pfmemalloc(page))
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			goto out;

	pfmemalloc_active = false;
out:
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	spin_unlock_irqrestore(&n->list_lock, flags);
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}

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static void *__ac_get_obj(struct kmem_cache *cachep, struct array_cache *ac,
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						gfp_t flags, bool force_refill)
{
	int i;
	void *objp = ac->entry[--ac->avail];

	/* Ensure the caller is allowed to use objects from PFMEMALLOC slab */
	if (unlikely(is_obj_pfmemalloc(objp))) {
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		struct kmem_cache_node *n;
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		if (gfp_pfmemalloc_allowed(flags)) {
			clear_obj_pfmemalloc(&objp);
			return objp;
		}

		/* The caller cannot use PFMEMALLOC objects, find another one */
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		for (i = 0; i < ac->avail; i++) {
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			/* If a !PFMEMALLOC object is found, swap them */
			if (!is_obj_pfmemalloc(ac->entry[i])) {
				objp = ac->entry[i];
				ac->entry[i] = ac->entry[ac->avail];
				ac->entry[ac->avail] = objp;
				return objp;
			}
		}

		/*
		 * If there are empty slabs on the slabs_free list and we are
		 * being forced to refill the cache, mark this one !pfmemalloc.
		 */
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		n = cachep->node[numa_mem_id()];
		if (!list_empty(&n->slabs_free) && force_refill) {
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			struct page *page = virt_to_head_page(objp);
			ClearPageSlabPfmemalloc(virt_to_head_page(page->s_mem));
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			clear_obj_pfmemalloc(&objp);
			recheck_pfmemalloc_active(cachep, ac);
			return objp;
		}

		/* No !PFMEMALLOC objects available */
		ac->avail++;
		objp = NULL;
	}

	return objp;
}

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static inline void *ac_get_obj(struct kmem_cache *cachep,
			struct array_cache *ac, gfp_t flags, bool force_refill)
{
	void *objp;

	if (unlikely(sk_memalloc_socks()))
		objp = __ac_get_obj(cachep, ac, flags, force_refill);
	else
		objp = ac->entry[--ac->avail];

	return objp;
}

static void *__ac_put_obj(struct kmem_cache *cachep, struct array_cache *ac,
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								void *objp)
{
	if (unlikely(pfmemalloc_active)) {
		/* Some pfmemalloc slabs exist, check if this is one */
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		struct page *page = virt_to_head_page(objp);
		struct page *mem_page = virt_to_head_page(page->s_mem);
		if (PageSlabPfmemalloc(mem_page))
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			set_obj_pfmemalloc(&objp);
	}

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	return objp;
}

static inline void ac_put_obj(struct kmem_cache *cachep, struct array_cache *ac,
								void *objp)
{
	if (unlikely(sk_memalloc_socks()))
		objp = __ac_put_obj(cachep, ac, objp);

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	ac->entry[ac->avail++] = objp;
}

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/*
 * Transfer objects in one arraycache to another.
 * Locking must be handled by the caller.
 *
 * Return the number of entries transferred.
 */
static int transfer_objects(struct array_cache *to,
		struct array_cache *from, unsigned int max)
{
	/* Figure out how many entries to transfer */
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	int nr = min3(from->avail, max, to->limit - to->avail);
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	if (!nr)
		return 0;

	memcpy(to->entry + to->avail, from->entry + from->avail -nr,
			sizeof(void *) *nr);

	from->avail -= nr;
	to->avail += nr;
	return nr;
}

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#ifndef CONFIG_NUMA

#define drain_alien_cache(cachep, alien) do { } while (0)
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#define reap_alien(cachep, n) do { } while (0)
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static inline struct array_cache **alloc_alien_cache(int node, int limit, gfp_t gfp)
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{
	return (struct array_cache **)BAD_ALIEN_MAGIC;
}

static inline void free_alien_cache(struct array_cache **ac_ptr)
{
}

static inline int cache_free_alien(struct kmem_cache *cachep, void *objp)
{
	return 0;
}

static inline void *alternate_node_alloc(struct kmem_cache *cachep,
		gfp_t flags)
{
	return NULL;
}

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static inline void *____cache_alloc_node(struct kmem_cache *cachep,
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		 gfp_t flags, int nodeid)
{
	return NULL;
}

#else	/* CONFIG_NUMA */

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static void *____cache_alloc_node(struct kmem_cache *, gfp_t, int);
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static void *alternate_node_alloc(struct kmem_cache *, gfp_t);
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static struct array_cache **alloc_alien_cache(int node, int limit, gfp_t gfp)
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{
	struct array_cache **ac_ptr;
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	int memsize = sizeof(void *) * nr_node_ids;
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	int i;

	if (limit > 1)
		limit = 12;
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	ac_ptr = kzalloc_node(memsize, gfp, node);
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	if (ac_ptr) {
		for_each_node(i) {
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			if (i == node || !node_online(i))
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				continue;
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			ac_ptr[i] = alloc_arraycache(node, limit, 0xbaadf00d, gfp);
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			if (!ac_ptr[i]) {
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				for (i--; i >= 0; i--)
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					kfree(ac_ptr[i]);
				kfree(ac_ptr);
				return NULL;
			}
		}
	}
	return ac_ptr;
}

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static void free_alien_cache(struct array_cache **ac_ptr)
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{
	int i;

	if (!ac_ptr)
		return;
	for_each_node(i)
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	    kfree(ac_ptr[i]);
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	kfree(ac_ptr);
}

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static void __drain_alien_cache(struct kmem_cache *cachep,
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				struct array_cache *ac, int node)
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{
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	struct kmem_cache_node *n = cachep->node[node];
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	if (ac->avail) {
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		spin_lock(&n->list_lock);
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		/*
		 * Stuff objects into the remote nodes shared array first.
		 * That way we could avoid the overhead of putting the objects
		 * into the free lists and getting them back later.
		 */
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		if (n->shared)
			transfer_objects(n->shared, ac, ac->limit);
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		free_block(cachep, ac->entry, ac->avail, node);
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		ac->avail = 0;
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		spin_unlock(&n->list_lock);
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	}
}

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/*
 * Called from cache_reap() to regularly drain alien caches round robin.
 */
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static void reap_alien(struct kmem_cache *cachep, struct kmem_cache_node *n)
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{
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	int node = __this_cpu_read(slab_reap_node);
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	if (n->alien) {
		struct array_cache *ac = n->alien[node];
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		if (ac && ac->avail && spin_trylock_irq(&ac->lock)) {
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			__drain_alien_cache(cachep, ac, node);
			spin_unlock_irq(&ac->lock);
		}
	}