slab.c 82.1 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
 * slabs and you must pass objects with the same intializations to
 * 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.
 *
 * The c_cpuarray may not be read with enabled local interrupts - 
 * it's changed with a smp_call_function().
 *
 * SMP synchronization:
 *  constructors and destructors are called without any locking.
 *  Several members in kmem_cache_t and struct slab never change, they
 *	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
 *	The global cache-chain is protected by the semaphore 'cache_chain_sem'.
 *	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.
 *
 */

#include	<linux/config.h>
#include	<linux/slab.h>
#include	<linux/mm.h>
#include	<linux/swap.h>
#include	<linux/cache.h>
#include	<linux/interrupt.h>
#include	<linux/init.h>
#include	<linux/compiler.h>
#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>
95
#include	<linux/string.h>
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#include	<asm/uaccess.h>
#include	<asm/cacheflush.h>
#include	<asm/tlbflush.h>
#include	<asm/page.h>

/*
 * DEBUG	- 1 for kmem_cache_create() to honour; SLAB_DEBUG_INITIAL,
 *		  SLAB_RED_ZONE & SLAB_POISON.
 *		  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 *)

#ifndef cache_line_size
#define cache_line_size()	L1_CACHE_BYTES
#endif

#ifndef ARCH_KMALLOC_MINALIGN
/*
 * Enforce a minimum alignment for the kmalloc caches.
 * Usually, the kmalloc caches are cache_line_size() aligned, except when
 * DEBUG and FORCED_DEBUG are enabled, then they are BYTES_PER_WORD aligned.
 * Some archs want to perform DMA into kmalloc caches and need a guaranteed
 * alignment larger than BYTES_PER_WORD. ARCH_KMALLOC_MINALIGN allows that.
 * Note that this flag disables some debug features.
 */
#define ARCH_KMALLOC_MINALIGN 0
#endif

#ifndef ARCH_SLAB_MINALIGN
/*
 * Enforce a minimum alignment for all caches.
 * Intended for archs that get misalignment faults even for BYTES_PER_WORD
 * aligned buffers. Includes ARCH_KMALLOC_MINALIGN.
 * If possible: Do not enable this flag for CONFIG_DEBUG_SLAB, it disables
 * some debug features.
 */
#define ARCH_SLAB_MINALIGN 0
#endif

#ifndef ARCH_KMALLOC_FLAGS
#define ARCH_KMALLOC_FLAGS SLAB_HWCACHE_ALIGN
#endif

/* Legal flag mask for kmem_cache_create(). */
#if DEBUG
# define CREATE_MASK	(SLAB_DEBUG_INITIAL | SLAB_RED_ZONE | \
			 SLAB_POISON | SLAB_HWCACHE_ALIGN | \
			 SLAB_NO_REAP | SLAB_CACHE_DMA | \
			 SLAB_MUST_HWCACHE_ALIGN | SLAB_STORE_USER | \
			 SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | \
			 SLAB_DESTROY_BY_RCU)
#else
# define CREATE_MASK	(SLAB_HWCACHE_ALIGN | SLAB_NO_REAP | \
			 SLAB_CACHE_DMA | SLAB_MUST_HWCACHE_ALIGN | \
			 SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | \
			 SLAB_DESTROY_BY_RCU)
#endif

/*
 * kmem_bufctl_t:
 *
 * Bufctl's are used for linking objs within a slab
 * linked offsets.
 *
 * This implementation relies on "struct page" for locating the cache &
 * slab an object belongs to.
 * This allows the bufctl structure to be small (one int), but limits
 * the number of objects a slab (not a cache) can contain when off-slab
 * bufctls are used. The limit is the size of the largest general cache
 * that does not use off-slab slabs.
 * For 32bit archs with 4 kB pages, is this 56.
 * This is not serious, as it is only for large objects, when it is unwise
 * to have too many per slab.
 * Note: This limit can be raised by introducing a general cache whose size
 * is less than 512 (PAGE_SIZE<<3), but greater than 256.
 */

#define BUFCTL_END	(((kmem_bufctl_t)(~0U))-0)
#define BUFCTL_FREE	(((kmem_bufctl_t)(~0U))-1)
#define	SLAB_LIMIT	(((kmem_bufctl_t)(~0U))-2)

/* Max number of objs-per-slab for caches which use off-slab slabs.
 * Needed to avoid a possible looping condition in cache_grow().
 */
static unsigned long offslab_limit;

/*
 * struct slab
 *
 * Manages the objs in a slab. Placed either at the beginning of mem allocated
 * for a slab, or allocated from an general cache.
 * Slabs are chained into three list: fully used, partial, fully free slabs.
 */
struct slab {
	struct list_head	list;
	unsigned long		colouroff;
	void			*s_mem;		/* including colour offset */
	unsigned int		inuse;		/* num of objs active in slab */
	kmem_bufctl_t		free;
};

/*
 * struct slab_rcu
 *
 * slab_destroy on a SLAB_DESTROY_BY_RCU cache uses this structure to
 * arrange for kmem_freepages to be called via RCU.  This is useful if
 * we need to approach a kernel structure obliquely, from its address
 * obtained without the usual locking.  We can lock the structure to
 * stabilize it and check it's still at the given address, only if we
 * can be sure that the memory has not been meanwhile reused for some
 * other kind of object (which our subsystem's lock might corrupt).
 *
 * rcu_read_lock before reading the address, then rcu_read_unlock after
 * taking the spinlock within the structure expected at that address.
 *
 * We assume struct slab_rcu can overlay struct slab when destroying.
 */
struct slab_rcu {
	struct rcu_head		head;
	kmem_cache_t		*cachep;
	void			*addr;
};

/*
 * struct array_cache
 *
 * Per cpu structures
 * 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;
};

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

/*
 * The slab lists of all objects.
 * Hopefully reduce the internal fragmentation
 * NUMA: The spinlock could be moved from the kmem_cache_t
 * into this structure, too. Figure out what causes
 * fewer cross-node spinlock operations.
 */
struct kmem_list3 {
	struct list_head	slabs_partial;	/* partial list first, better asm code */
	struct list_head	slabs_full;
	struct list_head	slabs_free;
	unsigned long	free_objects;
	int		free_touched;
	unsigned long	next_reap;
	struct array_cache	*shared;
};

#define LIST3_INIT(parent) \
	{ \
		.slabs_full	= LIST_HEAD_INIT(parent.slabs_full), \
		.slabs_partial	= LIST_HEAD_INIT(parent.slabs_partial), \
		.slabs_free	= LIST_HEAD_INIT(parent.slabs_free) \
	}
#define list3_data(cachep) \
	(&(cachep)->lists)

/* NUMA: per-node */
#define list3_data_ptr(cachep, ptr) \
		list3_data(cachep)

/*
 * kmem_cache_t
 *
 * manages a cache.
 */
	
struct kmem_cache_s {
/* 1) per-cpu data, touched during every alloc/free */
	struct array_cache	*array[NR_CPUS];
	unsigned int		batchcount;
	unsigned int		limit;
/* 2) touched by every alloc & free from the backend */
	struct kmem_list3	lists;
	/* NUMA: kmem_3list_t	*nodelists[MAX_NUMNODES] */
	unsigned int		objsize;
	unsigned int	 	flags;	/* constant flags */
	unsigned int		num;	/* # of objs per slab */
	unsigned int		free_limit; /* upper limit of objects in the lists */
	spinlock_t		spinlock;

/* 3) cache_grow/shrink */
	/* order of pgs per slab (2^n) */
	unsigned int		gfporder;

	/* force GFP flags, e.g. GFP_DMA */
	unsigned int		gfpflags;

	size_t			colour;		/* cache colouring range */
	unsigned int		colour_off;	/* colour offset */
	unsigned int		colour_next;	/* cache colouring */
	kmem_cache_t		*slabp_cache;
	unsigned int		slab_size;
	unsigned int		dflags;		/* dynamic flags */

	/* constructor func */
	void (*ctor)(void *, kmem_cache_t *, unsigned long);

	/* de-constructor func */
	void (*dtor)(void *, kmem_cache_t *, unsigned long);

/* 4) cache creation/removal */
	const char		*name;
	struct list_head	next;

/* 5) statistics */
#if STATS
	unsigned long		num_active;
	unsigned long		num_allocations;
	unsigned long		high_mark;
	unsigned long		grown;
	unsigned long		reaped;
	unsigned long 		errors;
	unsigned long		max_freeable;
	unsigned long		node_allocs;
	atomic_t		allochit;
	atomic_t		allocmiss;
	atomic_t		freehit;
	atomic_t		freemiss;
#endif
#if DEBUG
	int			dbghead;
	int			reallen;
#endif
};

#define CFLGS_OFF_SLAB		(0x80000000UL)
#define	OFF_SLAB(x)	((x)->flags & CFLGS_OFF_SLAB)

#define BATCHREFILL_LIMIT	16
/* Optimization question: fewer reaps means less 
 * probability for unnessary cpucache drain/refill cycles.
 *
 * OTHO the cpuarrays can contain lots of objects,
 * 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++)
#define	STATS_INC_REAPED(x)	((x)->reaped++)
#define	STATS_SET_HIGH(x)	do { if ((x)->num_active > (x)->high_mark) \
					(x)->high_mark = (x)->num_active; \
				} while (0)
#define	STATS_INC_ERR(x)	((x)->errors++)
#define	STATS_INC_NODEALLOCS(x)	((x)->node_allocs++)
#define	STATS_SET_FREEABLE(x, i) \
				do { if ((x)->max_freeable < i) \
					(x)->max_freeable = i; \
				} while (0)

#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)
#define	STATS_INC_REAPED(x)	do { } while (0)
#define	STATS_SET_HIGH(x)	do { } while (0)
#define	STATS_INC_ERR(x)	do { } while (0)
#define	STATS_INC_NODEALLOCS(x)	do { } while (0)
#define	STATS_SET_FREEABLE(x, i) \
				do { } while (0)

#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
/* Magic nums for obj red zoning.
 * Placed in the first word before and the first word after an obj.
 */
#define	RED_INACTIVE	0x5A2CF071UL	/* when obj is inactive */
#define	RED_ACTIVE	0x170FC2A5UL	/* when obj is active */

/* ...and for poisoning */
#define	POISON_INUSE	0x5a	/* for use-uninitialised poisoning */
#define POISON_FREE	0x6b	/* for use-after-free poisoning */
#define	POISON_END	0xa5	/* end-byte of poisoning */

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

static int obj_reallen(kmem_cache_t *cachep)
{
	return cachep->reallen;
}

static unsigned long *dbg_redzone1(kmem_cache_t *cachep, void *objp)
{
	BUG_ON(!(cachep->flags & SLAB_RED_ZONE));
	return (unsigned long*) (objp+obj_dbghead(cachep)-BYTES_PER_WORD);
}

static unsigned long *dbg_redzone2(kmem_cache_t *cachep, void *objp)
{
	BUG_ON(!(cachep->flags & SLAB_RED_ZONE));
	if (cachep->flags & SLAB_STORE_USER)
		return (unsigned long*) (objp+cachep->objsize-2*BYTES_PER_WORD);
	return (unsigned long*) (objp+cachep->objsize-BYTES_PER_WORD);
}

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

#else

#define obj_dbghead(x)			0
#define obj_reallen(cachep)		(cachep->objsize)
#define dbg_redzone1(cachep, objp)	({BUG(); (unsigned long *)NULL;})
#define dbg_redzone2(cachep, objp)	({BUG(); (unsigned long *)NULL;})
#define dbg_userword(cachep, objp)	({BUG(); (void **)NULL;})

#endif

/*
 * Maximum size of an obj (in 2^order pages)
 * and absolute limit for the gfp order.
 */
#if defined(CONFIG_LARGE_ALLOCS)
#define	MAX_OBJ_ORDER	13	/* up to 32Mb */
#define	MAX_GFP_ORDER	13	/* up to 32Mb */
#elif defined(CONFIG_MMU)
#define	MAX_OBJ_ORDER	5	/* 32 pages */
#define	MAX_GFP_ORDER	5	/* 32 pages */
#else
#define	MAX_OBJ_ORDER	8	/* up to 1Mb */
#define	MAX_GFP_ORDER	8	/* up to 1Mb */
#endif

/*
 * Do not go above this order unless 0 objects fit into the slab.
 */
#define	BREAK_GFP_ORDER_HI	1
#define	BREAK_GFP_ORDER_LO	0
static int slab_break_gfp_order = BREAK_GFP_ORDER_LO;

/* Macros for storing/retrieving the cachep and or slab from the
 * global 'mem_map'. These are used to find the slab an obj belongs to.
 * With kfree(), these are used to find the cache which an obj belongs to.
 */
#define	SET_PAGE_CACHE(pg,x)  ((pg)->lru.next = (struct list_head *)(x))
#define	GET_PAGE_CACHE(pg)    ((kmem_cache_t *)(pg)->lru.next)
#define	SET_PAGE_SLAB(pg,x)   ((pg)->lru.prev = (struct list_head *)(x))
#define	GET_PAGE_SLAB(pg)     ((struct slab *)(pg)->lru.prev)

/* These are the default caches for kmalloc. Custom caches can have other sizes. */
struct cache_sizes malloc_sizes[] = {
#define CACHE(x) { .cs_size = (x) },
#include <linux/kmalloc_sizes.h>
	CACHE(ULONG_MAX)
#undef CACHE
};
EXPORT_SYMBOL(malloc_sizes);

/* Must match cache_sizes above. Out of line to keep cache footprint low. */
struct cache_names {
	char *name;
	char *name_dma;
};

static struct cache_names __initdata cache_names[] = {
#define CACHE(x) { .name = "size-" #x, .name_dma = "size-" #x "(DMA)" },
#include <linux/kmalloc_sizes.h>
	{ NULL, }
#undef CACHE
};

static struct arraycache_init initarray_cache __initdata =
	{ { 0, BOOT_CPUCACHE_ENTRIES, 1, 0} };
static struct arraycache_init initarray_generic =
	{ { 0, BOOT_CPUCACHE_ENTRIES, 1, 0} };

/* internal cache of cache description objs */
static kmem_cache_t cache_cache = {
	.lists		= LIST3_INIT(cache_cache.lists),
	.batchcount	= 1,
	.limit		= BOOT_CPUCACHE_ENTRIES,
	.objsize	= sizeof(kmem_cache_t),
	.flags		= SLAB_NO_REAP,
	.spinlock	= SPIN_LOCK_UNLOCKED,
	.name		= "kmem_cache",
#if DEBUG
	.reallen	= sizeof(kmem_cache_t),
#endif
};

/* Guard access to the cache-chain. */
static struct semaphore	cache_chain_sem;
static struct list_head cache_chain;

/*
 * vm_enough_memory() looks at this to determine how many
 * slab-allocated pages are possibly freeable under pressure
 *
 * SLAB_RECLAIM_ACCOUNT turns this on per-slab
 */
atomic_t slab_reclaim_pages;
EXPORT_SYMBOL(slab_reclaim_pages);

/*
 * chicken and egg problem: delay the per-cpu array allocation
 * until the general caches are up.
 */
static enum {
	NONE,
	PARTIAL,
	FULL
} g_cpucache_up;

static DEFINE_PER_CPU(struct work_struct, reap_work);

static void free_block(kmem_cache_t* cachep, void** objpp, int len);
static void enable_cpucache (kmem_cache_t *cachep);
static void cache_reap (void *unused);

static inline void **ac_entry(struct array_cache *ac)
{
	return (void**)(ac+1);
}

static inline struct array_cache *ac_data(kmem_cache_t *cachep)
{
	return cachep->array[smp_processor_id()];
}

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static inline kmem_cache_t *__find_general_cachep(size_t size,
						unsigned int __nocast gfpflags)
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{
	struct cache_sizes *csizep = malloc_sizes;

#if DEBUG
	/* This happens if someone tries to call
 	* kmem_cache_create(), or __kmalloc(), before
 	* the generic caches are initialized.
 	*/
	BUG_ON(csizep->cs_cachep == NULL);
#endif
	while (size > csizep->cs_size)
		csizep++;

	/*
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	 * Really subtle: The last entry with cs->cs_size==ULONG_MAX
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	 * has cs_{dma,}cachep==NULL. Thus no special case
	 * for large kmalloc calls required.
	 */
	if (unlikely(gfpflags & GFP_DMA))
		return csizep->cs_dmacachep;
	return csizep->cs_cachep;
}

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kmem_cache_t *kmem_find_general_cachep(size_t size,
		unsigned int __nocast gfpflags)
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{
	return __find_general_cachep(size, gfpflags);
}
EXPORT_SYMBOL(kmem_find_general_cachep);

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/* Cal the num objs, wastage, and bytes left over for a given slab size. */
static void cache_estimate(unsigned long gfporder, size_t size, size_t align,
		 int flags, size_t *left_over, unsigned int *num)
{
	int i;
	size_t wastage = PAGE_SIZE<<gfporder;
	size_t extra = 0;
	size_t base = 0;

	if (!(flags & CFLGS_OFF_SLAB)) {
		base = sizeof(struct slab);
		extra = sizeof(kmem_bufctl_t);
	}
	i = 0;
	while (i*size + ALIGN(base+i*extra, align) <= wastage)
		i++;
	if (i > 0)
		i--;

	if (i > SLAB_LIMIT)
		i = SLAB_LIMIT;

	*num = i;
	wastage -= i*size;
	wastage -= ALIGN(base+i*extra, align);
	*left_over = wastage;
}

#define slab_error(cachep, msg) __slab_error(__FUNCTION__, cachep, msg)

static void __slab_error(const char *function, kmem_cache_t *cachep, char *msg)
{
	printk(KERN_ERR "slab error in %s(): cache `%s': %s\n",
		function, cachep->name, msg);
	dump_stack();
}

/*
 * 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.
 */
static void __devinit start_cpu_timer(int cpu)
{
	struct work_struct *reap_work = &per_cpu(reap_work, cpu);

	/*
	 * When this gets called from do_initcalls via cpucache_init(),
	 * init_workqueues() has already run, so keventd will be setup
	 * at that time.
	 */
	if (keventd_up() && reap_work->func == NULL) {
		INIT_WORK(reap_work, cache_reap, NULL);
		schedule_delayed_work_on(cpu, reap_work, HZ + 3 * cpu);
	}
}

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

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	if (cpu == -1)
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		nc = kmalloc(memsize, GFP_KERNEL);
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	else
		nc = kmalloc_node(memsize, GFP_KERNEL, cpu_to_node(cpu));

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	if (nc) {
		nc->avail = 0;
		nc->limit = entries;
		nc->batchcount = batchcount;
		nc->touched = 0;
	}
	return nc;
}

static int __devinit cpuup_callback(struct notifier_block *nfb,
				  unsigned long action, void *hcpu)
{
	long cpu = (long)hcpu;
	kmem_cache_t* cachep;

	switch (action) {
	case CPU_UP_PREPARE:
		down(&cache_chain_sem);
		list_for_each_entry(cachep, &cache_chain, next) {
			struct array_cache *nc;

			nc = alloc_arraycache(cpu, cachep->limit, cachep->batchcount);
			if (!nc)
				goto bad;

			spin_lock_irq(&cachep->spinlock);
			cachep->array[cpu] = nc;
			cachep->free_limit = (1+num_online_cpus())*cachep->batchcount
						+ cachep->num;
			spin_unlock_irq(&cachep->spinlock);

		}
		up(&cache_chain_sem);
		break;
	case CPU_ONLINE:
		start_cpu_timer(cpu);
		break;
#ifdef CONFIG_HOTPLUG_CPU
	case CPU_DEAD:
		/* fall thru */
	case CPU_UP_CANCELED:
		down(&cache_chain_sem);

		list_for_each_entry(cachep, &cache_chain, next) {
			struct array_cache *nc;

			spin_lock_irq(&cachep->spinlock);
			/* cpu is dead; no one can alloc from it. */
			nc = cachep->array[cpu];
			cachep->array[cpu] = NULL;
			cachep->free_limit -= cachep->batchcount;
			free_block(cachep, ac_entry(nc), nc->avail);
			spin_unlock_irq(&cachep->spinlock);
			kfree(nc);
		}
		up(&cache_chain_sem);
		break;
#endif
	}
	return NOTIFY_OK;
bad:
	up(&cache_chain_sem);
	return NOTIFY_BAD;
}

static struct notifier_block cpucache_notifier = { &cpuup_callback, NULL, 0 };

/* Initialisation.
 * Called after the gfp() functions have been enabled, and before smp_init().
 */
void __init kmem_cache_init(void)
{
	size_t left_over;
	struct cache_sizes *sizes;
	struct cache_names *names;

	/*
	 * Fragmentation resistance on low memory - only use bigger
	 * page orders on machines with more than 32MB of memory.
	 */
	if (num_physpages > (32 << 20) >> PAGE_SHIFT)
		slab_break_gfp_order = BREAK_GFP_ORDER_HI;

	
	/* Bootstrap is tricky, because several objects are allocated
	 * from caches that do not exist yet:
	 * 1) initialize the cache_cache cache: it contains the kmem_cache_t
	 *    structures of all caches, except cache_cache itself: cache_cache
	 *    is statically allocated.
	 *    Initially an __init data area is used for the head array, it's
	 *    replaced with a kmalloc allocated array at the end of the bootstrap.
	 * 2) Create the first kmalloc cache.
	 *    The kmem_cache_t for the new cache is allocated normally. An __init
	 *    data area is used for the head array.
	 * 3) Create the remaining kmalloc caches, with minimally sized head arrays.
	 * 4) Replace the __init data head arrays for cache_cache and the first
	 *    kmalloc cache with kmalloc allocated arrays.
	 * 5) Resize the head arrays of the kmalloc caches to their final sizes.
	 */

	/* 1) create the cache_cache */
	init_MUTEX(&cache_chain_sem);
	INIT_LIST_HEAD(&cache_chain);
	list_add(&cache_cache.next, &cache_chain);
	cache_cache.colour_off = cache_line_size();
	cache_cache.array[smp_processor_id()] = &initarray_cache.cache;

	cache_cache.objsize = ALIGN(cache_cache.objsize, cache_line_size());

	cache_estimate(0, cache_cache.objsize, cache_line_size(), 0,
				&left_over, &cache_cache.num);
	if (!cache_cache.num)
		BUG();

	cache_cache.colour = left_over/cache_cache.colour_off;
	cache_cache.colour_next = 0;
	cache_cache.slab_size = ALIGN(cache_cache.num*sizeof(kmem_bufctl_t) +
				sizeof(struct slab), cache_line_size());

	/* 2+3) create the kmalloc caches */
	sizes = malloc_sizes;
	names = cache_names;

	while (sizes->cs_size != ULONG_MAX) {
		/* For performance, all the general caches are L1 aligned.
		 * This should be particularly beneficial on SMP boxes, as it
		 * eliminates "false sharing".
		 * Note for systems short on memory removing the alignment will
		 * allow tighter packing of the smaller caches. */
		sizes->cs_cachep = kmem_cache_create(names->name,
			sizes->cs_size, ARCH_KMALLOC_MINALIGN,
			(ARCH_KMALLOC_FLAGS | SLAB_PANIC), NULL, NULL);

		/* Inc off-slab bufctl limit until the ceiling is hit. */
		if (!(OFF_SLAB(sizes->cs_cachep))) {
			offslab_limit = sizes->cs_size-sizeof(struct slab);
			offslab_limit /= sizeof(kmem_bufctl_t);
		}

		sizes->cs_dmacachep = kmem_cache_create(names->name_dma,
			sizes->cs_size, ARCH_KMALLOC_MINALIGN,
			(ARCH_KMALLOC_FLAGS | SLAB_CACHE_DMA | SLAB_PANIC),
			NULL, NULL);

		sizes++;
		names++;
	}
	/* 4) Replace the bootstrap head arrays */
	{
		void * ptr;
		
		ptr = kmalloc(sizeof(struct arraycache_init), GFP_KERNEL);
		local_irq_disable();
		BUG_ON(ac_data(&cache_cache) != &initarray_cache.cache);
		memcpy(ptr, ac_data(&cache_cache), sizeof(struct arraycache_init));
		cache_cache.array[smp_processor_id()] = ptr;
		local_irq_enable();
	
		ptr = kmalloc(sizeof(struct arraycache_init), GFP_KERNEL);
		local_irq_disable();
		BUG_ON(ac_data(malloc_sizes[0].cs_cachep) != &initarray_generic.cache);
		memcpy(ptr, ac_data(malloc_sizes[0].cs_cachep),
				sizeof(struct arraycache_init));
		malloc_sizes[0].cs_cachep->array[smp_processor_id()] = ptr;
		local_irq_enable();
	}

	/* 5) resize the head arrays to their final sizes */
	{
		kmem_cache_t *cachep;
		down(&cache_chain_sem);
		list_for_each_entry(cachep, &cache_chain, next)
			enable_cpucache(cachep);
		up(&cache_chain_sem);
	}

	/* Done! */
	g_cpucache_up = FULL;

	/* Register a cpu startup notifier callback
	 * that initializes ac_data for all new cpus
	 */
	register_cpu_notifier(&cpucache_notifier);
	

	/* The reap timers are started later, with a module init call:
	 * That part of the kernel is not yet operational.
	 */
}

static int __init cpucache_init(void)
{
	int cpu;

	/* 
	 * Register the timers that return unneeded
	 * pages to gfp.
	 */
	for (cpu = 0; cpu < NR_CPUS; cpu++) {
		if (cpu_online(cpu))
			start_cpu_timer(cpu);
	}

	return 0;
}

__initcall(cpucache_init);

/*
 * Interface to system's page allocator. No need to hold the cache-lock.
 *
 * If we requested dmaable memory, we will get it. Even if we
 * did not request dmaable memory, we might get it, but that
 * would be relatively rare and ignorable.
 */
static void *kmem_getpages(kmem_cache_t *cachep, unsigned int __nocast flags, int nodeid)
{
	struct page *page;
	void *addr;
	int i;

	flags |= cachep->gfpflags;
	if (likely(nodeid == -1)) {
		page = alloc_pages(flags, cachep->gfporder);
	} else {
		page = alloc_pages_node(nodeid, flags, cachep->gfporder);
	}
	if (!page)
		return NULL;
	addr = page_address(page);

	i = (1 << cachep->gfporder);
	if (cachep->flags & SLAB_RECLAIM_ACCOUNT)
		atomic_add(i, &slab_reclaim_pages);
	add_page_state(nr_slab, i);
	while (i--) {
		SetPageSlab(page);
		page++;
	}
	return addr;
}

/*
 * Interface to system's page release.
 */
static void kmem_freepages(kmem_cache_t *cachep, void *addr)
{
	unsigned long i = (1<<cachep->gfporder);
	struct page *page = virt_to_page(addr);
	const unsigned long nr_freed = i;

	while (i--) {
		if (!TestClearPageSlab(page))
			BUG();
		page++;
	}
	sub_page_state(nr_slab, nr_freed);
	if (current->reclaim_state)
		current->reclaim_state->reclaimed_slab += nr_freed;
	free_pages((unsigned long)addr, cachep->gfporder);
	if (cachep->flags & SLAB_RECLAIM_ACCOUNT) 
		atomic_sub(1<<cachep->gfporder, &slab_reclaim_pages);
}

static void kmem_rcu_free(struct rcu_head *head)
{
	struct slab_rcu *slab_rcu = (struct slab_rcu *) head;
	kmem_cache_t *cachep = slab_rcu->cachep;

	kmem_freepages(cachep, slab_rcu->addr);
	if (OFF_SLAB(cachep))
		kmem_cache_free(cachep->slabp_cache, slab_rcu);
}

#if DEBUG

#ifdef CONFIG_DEBUG_PAGEALLOC
static void store_stackinfo(kmem_cache_t *cachep, unsigned long *addr,
				unsigned long caller)
{
	int size = obj_reallen(cachep);

	addr = (unsigned long *)&((char*)addr)[obj_dbghead(cachep)];

	if (size < 5*sizeof(unsigned long))
		return;

	*addr++=0x12345678;
	*addr++=caller;
	*addr++=smp_processor_id();
	size -= 3*sizeof(unsigned long);
	{
		unsigned long *sptr = &caller;
		unsigned long svalue;

		while (!kstack_end(sptr)) {
			svalue = *sptr++;
			if (kernel_text_address(svalue)) {
				*addr++=svalue;
				size -= sizeof(unsigned long);
				if (size <= sizeof(unsigned long))
					break;
			}
		}

	}
	*addr++=0x87654321;
}
#endif

static void poison_obj(kmem_cache_t *cachep, void *addr, unsigned char val)
{