Re: [PATCH 1/5] slab: rename obj_reallen to obj_size

[Pekka Enberg <penberg@cs.helsinki.fi>]

Manfred,

How about this instead?

[PATCH] slab: distinguish between object and buffer sizes

An object cache has two different object lengths:

  - the amount of memory available for the user (object size)
  - the amount of memory allocated internally (buffer size)

This patch does some renames to make the code reflect that better.

Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
---

 slab.c |  154 +++++++++++++++++++++++++++++++++--------------------------------
 1 file changed, 80 insertions(+), 74 deletions(-)

Index: 2.6/mm/slab.c
===================================================================
--- 2.6.orig/mm/slab.c
+++ 2.6/mm/slab.c
@@ -374,7 +374,7 @@ struct kmem_cache {
 	unsigned int		batchcount;
 	unsigned int		limit;
 	unsigned int 		shared;
-	unsigned int		objsize;
+	unsigned int		buffer_size;
 /* 2) touched by every alloc & free from the backend */
 	struct kmem_list3	*nodelists[MAX_NUMNODES];
 	unsigned int	 	flags;	/* constant flags */
@@ -422,8 +422,14 @@ struct kmem_cache {
 	atomic_t		freemiss;
 #endif
 #if DEBUG
-	int			dbghead;
-	int			reallen;
+	/*
+	 * If debugging is enabled, then the allocator can add additional
+	 * fields and/or padding to every object. buffer_size contains the total
+	 * object size including these internal fields, the following two
+	 * variables contain the offset to the user object and its size.
+	 */
+	int			obj_offset;
+	int			obj_size;
 #endif
 };
 
@@ -494,49 +500,49 @@ struct kmem_cache {
 
 /* memory layout of objects:
  * 0		: objp
- * 0 .. cachep->dbghead - BYTES_PER_WORD - 1: padding. This ensures that
+ * 0 .. cachep->obj_offset - 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:
+ * cachep->obj_offset - BYTES_PER_WORD .. cachep->obj_offset - 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]
+ * cachep->obj_offset: The real object.
+ * cachep->buffer_size - 2* BYTES_PER_WORD: redzone word [BYTES_PER_WORD long]
+ * cachep->buffer_size - 1* BYTES_PER_WORD: last caller address [BYTES_PER_WORD long]
  */
-static int obj_dbghead(kmem_cache_t *cachep)
+static int obj_offset(kmem_cache_t *cachep)
 {
-	return cachep->dbghead;
+	return cachep->obj_offset;
 }
 
-static int obj_reallen(kmem_cache_t *cachep)
+static int obj_size(kmem_cache_t *cachep)
 {
-	return cachep->reallen;
+	return cachep->obj_size;
 }
 
 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);
+	return (unsigned long*) (objp+obj_offset(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);
+		return (unsigned long*) (objp+cachep->buffer_size-2*BYTES_PER_WORD);
+	return (unsigned long*) (objp+cachep->buffer_size-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);
+	return (void**)(objp+cachep->buffer_size-BYTES_PER_WORD);
 }
 
 #else
 
-#define obj_dbghead(x)			0
-#define obj_reallen(cachep)		(cachep->objsize)
+#define obj_offset(x)			0
+#define obj_size(cachep)		(cachep->buffer_size)
 #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;})
@@ -621,12 +627,12 @@ static kmem_cache_t cache_cache = {
 	.batchcount	= 1,
 	.limit		= BOOT_CPUCACHE_ENTRIES,
 	.shared		= 1,
-	.objsize	= sizeof(kmem_cache_t),
+	.buffer_size	= sizeof(kmem_cache_t),
 	.flags		= SLAB_NO_REAP,
 	.spinlock	= SPIN_LOCK_UNLOCKED,
 	.name		= "kmem_cache",
 #if DEBUG
-	.reallen	= sizeof(kmem_cache_t),
+	.obj_size	= sizeof(kmem_cache_t),
 #endif
 };
 
@@ -1052,9 +1058,9 @@ void __init kmem_cache_init(void)
 	cache_cache.array[smp_processor_id()] = &initarray_cache.cache;
 	cache_cache.nodelists[numa_node_id()] = &initkmem_list3[CACHE_CACHE];
 
-	cache_cache.objsize = ALIGN(cache_cache.objsize, cache_line_size());
+	cache_cache.buffer_size = ALIGN(cache_cache.buffer_size, cache_line_size());
 
-	cache_estimate(0, cache_cache.objsize, cache_line_size(), 0,
+	cache_estimate(0, cache_cache.buffer_size, cache_line_size(), 0,
 				&left_over, &cache_cache.num);
 	if (!cache_cache.num)
 		BUG();
@@ -1259,9 +1265,9 @@ static void kmem_rcu_free(struct rcu_hea
 static void store_stackinfo(kmem_cache_t *cachep, unsigned long *addr,
 				unsigned long caller)
 {
-	int size = obj_reallen(cachep);
+	int size = obj_size(cachep);
 
-	addr = (unsigned long *)&((char*)addr)[obj_dbghead(cachep)];
+	addr = (unsigned long *)&((char*)addr)[obj_offset(cachep)];
 
 	if (size < 5*sizeof(unsigned long))
 		return;
@@ -1291,8 +1297,8 @@ static void store_stackinfo(kmem_cache_t
 
 static void poison_obj(kmem_cache_t *cachep, void *addr, unsigned char val)
 {
-	int size = obj_reallen(cachep);
-	addr = &((char*)addr)[obj_dbghead(cachep)];
+	int size = obj_size(cachep);
+	addr = &((char*)addr)[obj_offset(cachep)];
 
 	memset(addr, val, size);
 	*(unsigned char *)(addr+size-1) = POISON_END;
@@ -1329,8 +1335,8 @@ static void print_objinfo(kmem_cache_t *
 				(unsigned long)*dbg_userword(cachep, objp));
 		printk("\n");
 	}
-	realobj = (char*)objp+obj_dbghead(cachep);
-	size = obj_reallen(cachep);
+	realobj = (char*)objp+obj_offset(cachep);
+	size = obj_size(cachep);
 	for (i=0; i<size && lines;i+=16, lines--) {
 		int limit;
 		limit = 16;
@@ -1346,8 +1352,8 @@ static void check_poison_obj(kmem_cache_
 	int size, i;
 	int lines = 0;
 
-	realobj = (char*)objp+obj_dbghead(cachep);
-	size = obj_reallen(cachep);
+	realobj = (char*)objp+obj_offset(cachep);
+	size = obj_size(cachep);
 
 	for (i=0;i<size;i++) {
 		char exp = POISON_FREE;
@@ -1382,17 +1388,17 @@ static void check_poison_obj(kmem_cache_
 		struct slab *slabp = page_get_slab(virt_to_page(objp));
 		int objnr;
 
-		objnr = (objp-slabp->s_mem)/cachep->objsize;
+		objnr = (objp-slabp->s_mem)/cachep->buffer_size;
 		if (objnr) {
-			objp = slabp->s_mem+(objnr-1)*cachep->objsize;
-			realobj = (char*)objp+obj_dbghead(cachep);
+			objp = slabp->s_mem+(objnr-1)*cachep->buffer_size;
+			realobj = (char*)objp+obj_offset(cachep);
 			printk(KERN_ERR "Prev obj: start=%p, len=%d\n",
 						realobj, size);
 			print_objinfo(cachep, objp, 2);
 		}
 		if (objnr+1 < cachep->num) {
-			objp = slabp->s_mem+(objnr+1)*cachep->objsize;
-			realobj = (char*)objp+obj_dbghead(cachep);
+			objp = slabp->s_mem+(objnr+1)*cachep->buffer_size;
+			realobj = (char*)objp+obj_offset(cachep);
 			printk(KERN_ERR "Next obj: start=%p, len=%d\n",
 						realobj, size);
 			print_objinfo(cachep, objp, 2);
@@ -1412,12 +1418,12 @@ static void slab_destroy (kmem_cache_t *
 #if DEBUG
 	int i;
 	for (i = 0; i < cachep->num; i++) {
-		void *objp = slabp->s_mem + cachep->objsize * i;
+		void *objp = slabp->s_mem + cachep->buffer_size * i;
 
 		if (cachep->flags & SLAB_POISON) {
 #ifdef CONFIG_DEBUG_PAGEALLOC
-			if ((cachep->objsize%PAGE_SIZE)==0 && OFF_SLAB(cachep))
-				kernel_map_pages(virt_to_page(objp), cachep->objsize/PAGE_SIZE,1);
+			if ((cachep->buffer_size%PAGE_SIZE)==0 && OFF_SLAB(cachep))
+				kernel_map_pages(virt_to_page(objp), cachep->buffer_size/PAGE_SIZE,1);
 			else
 				check_poison_obj(cachep, objp);
 #else
@@ -1433,13 +1439,13 @@ static void slab_destroy (kmem_cache_t *
 							"was overwritten");
 		}
 		if (cachep->dtor && !(cachep->flags & SLAB_POISON))
-			(cachep->dtor)(objp+obj_dbghead(cachep), cachep, 0);
+			(cachep->dtor)(objp+obj_offset(cachep), cachep, 0);
 	}
 #else
 	if (cachep->dtor) {
 		int i;
 		for (i = 0; i < cachep->num; i++) {
-			void* objp = slabp->s_mem+cachep->objsize*i;
+			void* objp = slabp->s_mem+cachep->buffer_size*i;
 			(cachep->dtor)(objp, cachep, 0);
 		}
 	}
@@ -1459,7 +1465,7 @@ static void slab_destroy (kmem_cache_t *
 	}
 }
 
-/* For setting up all the kmem_list3s for cache whose objsize is same
+/* For setting up all the kmem_list3s for cache whose buffer_size is same
    as size of kmem_list3. */
 static inline void set_up_list3s(kmem_cache_t *cachep, int index)
 {
@@ -1546,7 +1552,7 @@ kmem_cache_create (const char *name, siz
 		set_fs(old_fs);
 		if (res) {
 			printk("SLAB: cache with size %d has lost its name\n",
-					pc->objsize);
+					pc->buffer_size);
 			continue;
 		}
 
@@ -1637,14 +1643,14 @@ kmem_cache_create (const char *name, siz
 	memset(cachep, 0, sizeof(kmem_cache_t));
 
 #if DEBUG
-	cachep->reallen = size;
+	cachep->obj_size = size;
 
 	if (flags & SLAB_RED_ZONE) {
 		/* redzoning only works with word aligned caches */
 		align = BYTES_PER_WORD;
 
 		/* add space for red zone words */
-		cachep->dbghead += BYTES_PER_WORD;
+		cachep->obj_offset += BYTES_PER_WORD;
 		size += 2*BYTES_PER_WORD;
 	}
 	if (flags & SLAB_STORE_USER) {
@@ -1656,8 +1662,8 @@ kmem_cache_create (const char *name, siz
 		size += BYTES_PER_WORD;
 	}
 #if FORCED_DEBUG && defined(CONFIG_DEBUG_PAGEALLOC)
-	if (size >= malloc_sizes[INDEX_L3+1].cs_size && cachep->reallen > cache_line_size() && size < PAGE_SIZE) {
-		cachep->dbghead += PAGE_SIZE - size;
+	if (size >= malloc_sizes[INDEX_L3+1].cs_size && cachep->obj_size > cache_line_size() && size < PAGE_SIZE) {
+		cachep->obj_offset += PAGE_SIZE - size;
 		size = PAGE_SIZE;
 	}
 #endif
@@ -1757,7 +1763,7 @@ next:
 	if (flags & SLAB_CACHE_DMA)
 		cachep->gfpflags |= GFP_DMA;
 	spin_lock_init(&cachep->spinlock);
-	cachep->objsize = size;
+	cachep->buffer_size = size;
 
 	if (flags & CFLGS_OFF_SLAB)
 		cachep->slabp_cache = kmem_find_general_cachep(slab_size, 0u);
@@ -2089,7 +2095,7 @@ static void cache_init_objs(kmem_cache_t
 	int i;
 
 	for (i = 0; i < cachep->num; i++) {
-		void *objp = slabp->s_mem+cachep->objsize*i;
+		void *objp = slabp->s_mem+cachep->buffer_size*i;
 #if DEBUG
 		/* need to poison the objs? */
 		if (cachep->flags & SLAB_POISON)
@@ -2107,7 +2113,7 @@ static void cache_init_objs(kmem_cache_t
 		 * Otherwise, deadlock. They must also be threaded.
 		 */
 		if (cachep->ctor && !(cachep->flags & SLAB_POISON))
-			cachep->ctor(objp+obj_dbghead(cachep), cachep, ctor_flags);
+			cachep->ctor(objp+obj_offset(cachep), cachep, ctor_flags);
 
 		if (cachep->flags & SLAB_RED_ZONE) {
 			if (*dbg_redzone2(cachep, objp) != RED_INACTIVE)
@@ -2117,8 +2123,8 @@ static void cache_init_objs(kmem_cache_t
 				slab_error(cachep, "constructor overwrote the"
 							" start of an object");
 		}
-		if ((cachep->objsize % PAGE_SIZE) == 0 && OFF_SLAB(cachep) && cachep->flags & SLAB_POISON)
-	       		kernel_map_pages(virt_to_page(objp), cachep->objsize/PAGE_SIZE, 0);
+		if ((cachep->buffer_size % PAGE_SIZE) == 0 && OFF_SLAB(cachep) && cachep->flags & SLAB_POISON)
+	       		kernel_map_pages(virt_to_page(objp), cachep->buffer_size/PAGE_SIZE, 0);
 #else
 		if (cachep->ctor)
 			cachep->ctor(objp, cachep, ctor_flags);
@@ -2276,7 +2282,7 @@ static void *cache_free_debugcheck(kmem_
 	unsigned int objnr;
 	struct slab *slabp;
 
-	objp -= obj_dbghead(cachep);
+	objp -= obj_offset(cachep);
 	kfree_debugcheck(objp);
 	page = virt_to_page(objp);
 
@@ -2302,30 +2308,30 @@ static void *cache_free_debugcheck(kmem_
 	if (cachep->flags & SLAB_STORE_USER)
 		*dbg_userword(cachep, objp) = caller;
 
-	objnr = (objp-slabp->s_mem)/cachep->objsize;
+	objnr = (objp-slabp->s_mem)/cachep->buffer_size;
 
 	BUG_ON(objnr >= cachep->num);
-	BUG_ON(objp != slabp->s_mem + objnr*cachep->objsize);
+	BUG_ON(objp != slabp->s_mem + objnr*cachep->buffer_size);
 
 	if (cachep->flags & SLAB_DEBUG_INITIAL) {
 		/* Need to call the slab's constructor so the
 		 * caller can perform a verify of its state (debugging).
 		 * Called without the cache-lock held.
 		 */
-		cachep->ctor(objp+obj_dbghead(cachep),
+		cachep->ctor(objp+obj_offset(cachep),
 					cachep, SLAB_CTOR_CONSTRUCTOR|SLAB_CTOR_VERIFY);
 	}
 	if (cachep->flags & SLAB_POISON && cachep->dtor) {
 		/* we want to cache poison the object,
 		 * call the destruction callback
 		 */
-		cachep->dtor(objp+obj_dbghead(cachep), cachep, 0);
+		cachep->dtor(objp+obj_offset(cachep), cachep, 0);
 	}
 	if (cachep->flags & SLAB_POISON) {
 #ifdef CONFIG_DEBUG_PAGEALLOC
-		if ((cachep->objsize % PAGE_SIZE) == 0 && OFF_SLAB(cachep)) {
+		if ((cachep->buffer_size % PAGE_SIZE) == 0 && OFF_SLAB(cachep)) {
 			store_stackinfo(cachep, objp, (unsigned long)caller);
-	       		kernel_map_pages(virt_to_page(objp), cachep->objsize/PAGE_SIZE, 0);
+	       		kernel_map_pages(virt_to_page(objp), cachep->buffer_size/PAGE_SIZE, 0);
 		} else {
 			poison_obj(cachep, objp, POISON_FREE);
 		}
@@ -2425,7 +2431,7 @@ retry:
 
 			/* get obj pointer */
 			ac->entry[ac->avail++] = slabp->s_mem +
-				slabp->free*cachep->objsize;
+				slabp->free*cachep->buffer_size;
 
 			slabp->inuse++;
 			next = slab_bufctl(slabp)[slabp->free];
@@ -2484,8 +2490,8 @@ cache_alloc_debugcheck_after(kmem_cache_
 		return objp;
  	if (cachep->flags & SLAB_POISON) {
 #ifdef CONFIG_DEBUG_PAGEALLOC
-		if ((cachep->objsize % PAGE_SIZE) == 0 && OFF_SLAB(cachep))
-			kernel_map_pages(virt_to_page(objp), cachep->objsize/PAGE_SIZE, 1);
+		if ((cachep->buffer_size % PAGE_SIZE) == 0 && OFF_SLAB(cachep))
+			kernel_map_pages(virt_to_page(objp), cachep->buffer_size/PAGE_SIZE, 1);
 		else
 			check_poison_obj(cachep, objp);
 #else
@@ -2506,7 +2512,7 @@ cache_alloc_debugcheck_after(kmem_cache_
 		*dbg_redzone1(cachep, objp) = RED_ACTIVE;
 		*dbg_redzone2(cachep, objp) = RED_ACTIVE;
 	}
-	objp += obj_dbghead(cachep);
+	objp += obj_offset(cachep);
 	if (cachep->ctor && cachep->flags & SLAB_POISON) {
 		unsigned long	ctor_flags = SLAB_CTOR_CONSTRUCTOR;
 
@@ -2592,7 +2598,7 @@ retry:
  	BUG_ON(slabp->inuse == cachep->num);
 
  	/* get obj pointer */
- 	obj =  slabp->s_mem + slabp->free*cachep->objsize;
+ 	obj =  slabp->s_mem + slabp->free*cachep->buffer_size;
  	slabp->inuse++;
  	next = slab_bufctl(slabp)[slabp->free];
 #if DEBUG
@@ -2642,7 +2648,7 @@ static void free_block(kmem_cache_t *cac
 		slabp = page_get_slab(virt_to_page(objp));
 		l3 = cachep->nodelists[node];
 		list_del(&slabp->list);
-		objnr = (objp - slabp->s_mem) / cachep->objsize;
+		objnr = (objp - slabp->s_mem) / cachep->buffer_size;
 		check_spinlock_acquired_node(cachep, node);
 		check_slabp(cachep, slabp);
 
@@ -2825,7 +2831,7 @@ int fastcall kmem_ptr_validate(kmem_cach
 	unsigned long addr = (unsigned long) ptr;
 	unsigned long min_addr = PAGE_OFFSET;
 	unsigned long align_mask = BYTES_PER_WORD-1;
-	unsigned long size = cachep->objsize;
+	unsigned long size = cachep->buffer_size;
 	struct page *page;
 
 	if (unlikely(addr < min_addr))
@@ -3069,7 +3075,7 @@ EXPORT_SYMBOL(free_percpu);
 
 unsigned int kmem_cache_size(kmem_cache_t *cachep)
 {
-	return obj_reallen(cachep);
+	return obj_size(cachep);
 }
 EXPORT_SYMBOL(kmem_cache_size);
 
@@ -3213,13 +3219,13 @@ static void enable_cpucache(kmem_cache_t
 	 * The numbers are guessed, we should auto-tune as described by
 	 * Bonwick.
 	 */
-	if (cachep->objsize > 131072)
+	if (cachep->buffer_size > 131072)
 		limit = 1;
-	else if (cachep->objsize > PAGE_SIZE)
+	else if (cachep->buffer_size > PAGE_SIZE)
 		limit = 8;
-	else if (cachep->objsize > 1024)
+	else if (cachep->buffer_size > 1024)
 		limit = 24;
-	else if (cachep->objsize > 256)
+	else if (cachep->buffer_size > 256)
 		limit = 54;
 	else
 		limit = 120;
@@ -3234,7 +3240,7 @@ static void enable_cpucache(kmem_cache_t
 	 */
 	shared = 0;
 #ifdef CONFIG_SMP
-	if (cachep->objsize <= PAGE_SIZE)
+	if (cachep->buffer_size <= PAGE_SIZE)
 		shared = 8;
 #endif
 
@@ -3381,7 +3387,7 @@ static void *s_start(struct seq_file *m,
 #else
 		seq_puts(m, "slabinfo - version: 2.1\n");
 #endif
-		seq_puts(m, "# name            <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab>");
+		seq_puts(m, "# name            <active_objs> <num_objs> <buffer_size> <objperslab> <pagesperslab>");
 		seq_puts(m, " : tunables <limit> <batchcount> <sharedfactor>");
 		seq_puts(m, " : slabdata <active_slabs> <num_slabs> <sharedavail>");
 #if STATS
@@ -3475,7 +3481,7 @@ static int s_show(struct seq_file *m, vo
 		printk(KERN_ERR "slab: cache %s error: %s\n", name, error);
 
 	seq_printf(m, "%-17s %6lu %6lu %6u %4u %4d",
-		name, active_objs, num_objs, cachep->objsize,
+		name, active_objs, num_objs, cachep->buffer_size,
 		cachep->num, (1<<cachep->gfporder));
 	seq_printf(m, " : tunables %4u %4u %4u",
 			cachep->limit, cachep->batchcount,
@@ -3607,7 +3613,7 @@ unsigned int ksize(const void *objp)
 	if (unlikely(objp == NULL))
 		return 0;
 
-	return obj_reallen(page_get_cache(virt_to_page(objp)));
+	return obj_size(page_get_cache(virt_to_page(objp)));
 }
 
 


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