[patch 06/17] SLUB: Slab defrag core

[patch 06/17] SLUB: Slab defrag core

[Christoph Lameter]

[-- Attachment #1: 0052-SLUB-Slab-defrag-core.patch --]
[-- Type: text/plain, Size: 14495 bytes --]

Slab defragmentation may occur:

1. Unconditionally when kmem_cache_shrink is called on a slab cache by the
   kernel calling kmem_cache_shrink.

2. Use of the slabinfo command line to trigger slab shrinking.

3. Per node defrag conditionally when kmem_cache_defrag(<node>) is called.

   Defragmentation is only performed if the fragmentation of the slab
   is lower than the specified percentage. Fragmentation ratios are measured
   by calculating the percentage of objects in use compared to the total
   number of objects that the slab cache could hold without extending it.

   kmem_cache_defrag() takes a node parameter. This can either be -1 if
   defragmentation should be performed on all nodes, or a node number.
   If a node number was specified then defragmentation is only performed
   on a specific node.

   Slab defragmentation is a memory intensive operation that can be
   sped up in a NUMA system if mostly node local memory is accessed. It is
   possible to run shrinking on a node after execution of shrink_slabs().

A couple of functions must be setup via a call to kmem_cache_setup_defrag()
in order for a slabcache to support defragmentation. These are

void *get(struct kmem_cache *s, int nr, void **objects)

	Must obtain a reference to the listed objects. SLUB guarantees that
	the objects are still allocated. However, other threads may be blocked
	in slab_free() attempting to free objects in the slab. These may succeed
	as soon as get() returns to the slab allocator. The function must
	be able to detect such situations and void the attempts to free such
	objects (by for example voiding the corresponding entry in the objects
	array).

	No slab operations may be performed in get(). Interrupts
	are disabled. What can be done is very limited. The slab lock
	for the page that contains the object is taken. Any attempt to perform
	a slab operation may lead to a deadlock.

	get() returns a private pointer that is passed to kick. Should we
	be unable to obtain all references then that pointer may indicate
	to the kick() function that it should not attempt any object removal
	or move but simply remove the reference counts.

void kick(struct kmem_cache *, int nr, void **objects, void *get_result)

	After SLUB has established references to the objects in a
	slab it will then drop all locks and use kick() to move objects out
	of the slab. The existence of the object is guaranteed by virtue of
	the earlier obtained references via get(). The callback may perform
	any slab operation since no locks are held at the time of call.

	The callback should remove the object from the slab in some way. This
	may be accomplished by reclaiming the object and then running
	kmem_cache_free() or reallocating it and then running
	kmem_cache_free(). Reallocation is advantageous because the partial
	slabs were just sorted to have the partial slabs with the most objects
	first. Reallocation is likely to result in filling up a slab in
	addition to freeing up one slab. A filled up slab can also be removed
	from the partial list. So there could be a double effect.

	Kick() does not return a result. SLUB will check the number of
	remaining objects in the slab. If all objects were removed then
	we know that the operation was successful.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 include/linux/slab_def.h |    1 
 include/linux/slob_def.h |    1 
 include/linux/slub_def.h |    1 
 mm/slub.c                |  273 +++++++++++++++++++++++++++++++++++++----------
 4 files changed, 218 insertions(+), 58 deletions(-)

Index: linux-2.6.24-rc2-mm1/mm/slub.c
===================================================================
--- linux-2.6.24-rc2-mm1.orig/mm/slub.c	2007-11-14 13:39:56.920538689 -0800
+++ linux-2.6.24-rc2-mm1/mm/slub.c	2007-11-14 13:54:06.778195430 -0800
@@ -143,14 +143,14 @@
  * Mininum number of partial slabs. These will be left on the partial
  * lists even if they are empty. kmem_cache_shrink may reclaim them.
  */
-#define MIN_PARTIAL 2
+#define MIN_PARTIAL 5
 
 /*
  * Maximum number of desirable partial slabs.
- * The existence of more partial slabs makes kmem_cache_shrink
- * sort the partial list by the number of objects in the.
+ * More slabs cause kmem_cache_shrink to sort the slabs by objects
+ * and triggers slab defragmentation.
  */
-#define MAX_PARTIAL 10
+#define MAX_PARTIAL 20
 
 #define DEBUG_DEFAULT_FLAGS (SLAB_DEBUG_FREE | SLAB_RED_ZONE | \
 				SLAB_POISON | SLAB_STORE_USER)
@@ -2802,80 +2802,237 @@ static unsigned long count_partial(struc
 	return x;
 }
 
+ /*
+ * Vacate all objects in the given slab.
+  *
+ * The scratch aread passed to list function is sufficient to hold
+ * struct listhead times objects per slab. We use it to hold void ** times
+ * objects per slab plus a bitmap for each object.
+*/
+static int kmem_cache_vacate(struct page *page, void *scratch)
+{
+	void **vector = scratch;
+	void *p;
+	void *addr = page_address(page);
+	struct kmem_cache *s;
+	unsigned long *map;
+	int leftover;
+	int objects;
+	void *private;
+	unsigned long flags;
+	unsigned long state;
+
+	BUG_ON(!PageSlab(page));
+	local_irq_save(flags);
+	state = slab_lock(page);
+	BUG_ON(!(state & FROZEN));
+
+	s = page->slab;
+	map = scratch + max_defrag_slab_objects * sizeof(void **);
+	if (!page->inuse || !s->kick)
+		goto out;
+
+	/* Determine used objects */
+	bitmap_fill(map, s->objects);
+	for_each_free_object(p, s, page->freelist)
+			__clear_bit(slab_index(p, s, addr), map);
+
+	objects = 0;
+	memset(vector, 0, s->objects * sizeof(void **));
+	for_each_object(p, s, addr)
+		if (test_bit(slab_index(p, s, addr), map))
+			vector[objects++] = p;
+
+	private = s->get(s, objects, vector);
+
+	/*
+	 * Got references. Now we can drop the slab lock. The slab
+	 * is frozen so it cannot vanish from under us nor will
+	 * allocations be performed on the slab. However, unlocking the
+	 * slab will allow concurrent slab_frees to proceed.
+	 */
+	slab_unlock(page, state);
+	local_irq_restore(flags);
+
+	/*
+	 * Perform the KICK callbacks to remove the objects.
+	 */
+	s->kick(s, objects, vector, private);
+
+	local_irq_save(flags);
+	state = slab_lock(page);
+out:
+	/*
+	 * Check the result and unfreeze the slab
+	 */
+	leftover = page->inuse;
+	unfreeze_slab(s, page, leftover > 0, state);
+	local_irq_restore(flags);
+	return leftover;
+}
+
 /*
- * kmem_cache_shrink removes empty slabs from the partial lists and sorts
- * the remaining slabs by the number of items in use. The slabs with the
- * most items in use come first. New allocations will then fill those up
- * and thus they can be removed from the partial lists.
- *
- * The slabs with the least items are placed last. This results in them
- * being allocated from last increasing the chance that the last objects
- * are freed in them.
+ * Remove objects from a list of slab pages that have been gathered.
+ * Must be called with slabs that have been isolated before.
  */
-int kmem_cache_shrink(struct kmem_cache *s)
+int kmem_cache_reclaim(struct list_head *zaplist)
 {
-	int node;
-	int i;
-	struct kmem_cache_node *n;
+	int freed = 0;
+	void **scratch;
 	struct page *page;
-	struct page *t;
-	struct list_head *slabs_by_inuse =
-		kmalloc(sizeof(struct list_head) * s->objects, GFP_KERNEL);
-	unsigned long flags;
-	unsigned long state;
+	struct page *page2;
 
-	if (!slabs_by_inuse)
-		return -ENOMEM;
+	if (list_empty(zaplist))
+		return 0;
 
-	flush_all(s);
-	for_each_node_state(node, N_NORMAL_MEMORY) {
-		n = get_node(s, node);
+	scratch = alloc_scratch();
+	if (!scratch)
+		return 0;
 
-		if (!n->nr_partial)
-			continue;
+	list_for_each_entry_safe(page, page2, zaplist, lru) {
+		list_del(&page->lru);
+		if (kmem_cache_vacate(page, scratch) == 0)
+				freed++;
+	}
+	kfree(scratch);
+	return freed;
+}
 
-		for (i = 0; i < s->objects; i++)
-			INIT_LIST_HEAD(slabs_by_inuse + i);
+/*
+ * Shrink the slab cache on a particular node of the cache
+ * by releasing slabs with zero objects and trying to reclaim
+ * slabs with less than a quarter of objects allocated.
+ */
+static unsigned long __kmem_cache_shrink(struct kmem_cache *s,
+	struct kmem_cache_node *n)
+{
+	unsigned long flags;
+	struct page *page, *page2;
+	LIST_HEAD(zaplist);
+	int freed = 0;
+	unsigned long state;
 
-		spin_lock_irqsave(&n->list_lock, flags);
+	spin_lock_irqsave(&n->list_lock, flags);
+	list_for_each_entry_safe(page, page2, &n->partial, lru) {
+		if (page->inuse > s->objects / 4)
+			continue;
+		state = slab_trylock(page);
+		if (!state)
+			continue;
 
-		/*
-		 * Build lists indexed by the items in use in each slab.
-		 *
-		 * Note that concurrent frees may occur while we hold the
-		 * list_lock. page->inuse here is the upper limit.
-		 */
-		list_for_each_entry_safe(page, t, &n->partial, lru) {
-			if (page->inuse) {
-				list_move(&page->lru,
-				slabs_by_inuse + page->inuse);
-				continue;
+		if (page->inuse) {
+
+			list_move(&page->lru, &zaplist);
+			if (s->kick) {
+				n->nr_partial--;
+				state |= FROZEN;
 			}
-			state = slab_trylock(page);
-			if (!state)
-				continue;
-			/*
-			 * Must hold slab lock here because slab_free may have
-			 * freed the last object and be waiting to release the
-			 * slab.
-			 */
+			slab_unlock(page, state);
+
+		} else {
 			list_del(&page->lru);
 			n->nr_partial--;
 			slab_unlock(page, state);
 			discard_slab(s, page);
+			freed++;
 		}
+	}
 
-		/*
-		 * Rebuild the partial list with the slabs filled up most
-		 * first and the least used slabs at the end.
-		 */
-		for (i = s->objects - 1; i >= 0; i--)
-			list_splice(slabs_by_inuse + i, n->partial.prev);
+	if (!s->kick)
+		/* Simply put the zaplist at the end */
+		list_splice(&zaplist, n->partial.prev);
 
-		spin_unlock_irqrestore(&n->list_lock, flags);
+	spin_unlock_irqrestore(&n->list_lock, flags);
+
+	if (s->kick)
+		freed += kmem_cache_reclaim(&zaplist);
+	return freed;
+}
+
+static unsigned long __kmem_cache_defrag(struct kmem_cache *s, int node)
+{
+	unsigned long capacity;
+	unsigned long objects_in_full_slabs;
+	unsigned long ratio;
+	struct kmem_cache_node *n = get_node(s, node);
+
+	/*
+	 * An insignificant number of partial slabs means that the
+	 * slab cache does not need any defragmentation.
+	 */
+	if (n->nr_partial <= MAX_PARTIAL)
+		return 0;
+
+	capacity = atomic_long_read(&n->nr_slabs) * s->objects;
+	objects_in_full_slabs =
+			(atomic_long_read(&n->nr_slabs) - n->nr_partial)
+							* s->objects;
+	/*
+	 * Worst case calculation: If we would be over the ratio
+	 * even if all partial slabs would only have one object
+	 * then we can skip the next test that requires a scan
+	 * through all the partial page structs to sum up the actual
+	 * number of objects in the partial slabs.
+	 */
+	ratio = (objects_in_full_slabs + 1 * n->nr_partial) * 100 / capacity;
+	if (ratio > s->defrag_ratio)
+		return 0;
+
+	/*
+	 * Now for the real calculation. If usage ratio is more than required
+	 * then no defragmentation is necessary.
+	 */
+	ratio = (objects_in_full_slabs + count_partial(n)) * 100 / capacity;
+	if (ratio > s->defrag_ratio)
+		return 0;
+
+	return __kmem_cache_shrink(s, n) << s->order;
+}
+
+/*
+ * Defrag slabs conditional on the amount of fragmentation on each node.
+ */
+int kmem_cache_defrag(int node)
+{
+	struct kmem_cache *s;
+	unsigned long pages = 0;
+
+	/*
+	 * kmem_cache_defrag may be called from the reclaim path which may be
+	 * called for any page allocator alloc. So there is the danger that we
+	 * get called in a situation where slub already acquired the slub_lock
+	 * for other purposes.
+	 */
+	if (!down_read_trylock(&slub_lock))
+		return 0;
+
+	list_for_each_entry(s, &slab_caches, list) {
+		if (node == -1) {
+			int nid;
+
+			for_each_node_state(nid, N_NORMAL_MEMORY)
+				pages += __kmem_cache_defrag(s, nid);
+		} else
+			pages += __kmem_cache_defrag(s, node);
 	}
+	up_read(&slub_lock);
+	return pages;
+}
+EXPORT_SYMBOL(kmem_cache_defrag);
+
+/*
+ * kmem_cache_shrink removes empty slabs from the partial lists.
+ * If the slab cache support defragmentation then objects are
+ * reclaimed.
+ */
+int kmem_cache_shrink(struct kmem_cache *s)
+{
+	int node;
+
+	flush_all(s);
+	for_each_node_state(node, N_NORMAL_MEMORY)
+		__kmem_cache_shrink(s, get_node(s, node));
 
-	kfree(slabs_by_inuse);
 	return 0;
 }
 EXPORT_SYMBOL(kmem_cache_shrink);
Index: linux-2.6.24-rc2-mm1/include/linux/slab_def.h
===================================================================
--- linux-2.6.24-rc2-mm1.orig/include/linux/slab_def.h	2007-11-14 13:39:56.904538982 -0800
+++ linux-2.6.24-rc2-mm1/include/linux/slab_def.h	2007-11-14 13:39:56.936039109 -0800
@@ -101,5 +101,6 @@ ssize_t slabinfo_write(struct file *, co
 static inline void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private)) {}
+static inline int kmem_cache_defrag(int node) { return 0; }
 
 #endif	/* _LINUX_SLAB_DEF_H */
Index: linux-2.6.24-rc2-mm1/include/linux/slob_def.h
===================================================================
--- linux-2.6.24-rc2-mm1.orig/include/linux/slob_def.h	2007-11-14 13:39:56.904538982 -0800
+++ linux-2.6.24-rc2-mm1/include/linux/slob_def.h	2007-11-14 13:39:56.936039109 -0800
@@ -36,5 +36,6 @@ static inline void *__kmalloc(size_t siz
 static inline void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private)) {}
+static inline int kmem_cache_defrag(int node) { return 0; }
 
 #endif /* __LINUX_SLOB_DEF_H */
Index: linux-2.6.24-rc2-mm1/include/linux/slub_def.h
===================================================================
--- linux-2.6.24-rc2-mm1.orig/include/linux/slub_def.h	2007-11-14 13:39:56.900538713 -0800
+++ linux-2.6.24-rc2-mm1/include/linux/slub_def.h	2007-11-14 13:39:56.936039109 -0800
@@ -245,5 +245,6 @@ static __always_inline void *kmalloc_nod
 void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private));
+int kmem_cache_defrag(int node);
 
 #endif /* _LINUX_SLUB_DEF_H */

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Re: [patch 06/17] SLUB: Slab defrag core

[KAMEZAWA Hiroyuki]

On Wed, 14 Nov 2007 14:09:12 -0800
Christoph Lameter <clameter@sgi.com> wrote:

> void kick(struct kmem_cache *, int nr, void **objects, void *get_result)
> 
> 	After SLUB has established references to the objects in a
> 	slab it will then drop all locks and use kick() to move objects out
> 	of the slab. The existence of the object is guaranteed by virtue of
> 	the earlier obtained references via get(). The callback may perform
> 	any slab operation since no locks are held at the time of call.
> 
> 	The callback should remove the object from the slab in some way. This
> 	may be accomplished by reclaiming the object and then running
> 	kmem_cache_free() or reallocating it and then running
> 	kmem_cache_free(). Reallocation is advantageous because the partial
> 	slabs were just sorted to have the partial slabs with the most objects
> 	first. Reallocation is likely to result in filling up a slab in
> 	addition to freeing up one slab. A filled up slab can also be removed
> 	from the partial list. So there could be a double effect.
> 

I think shrink_slab()? is called under memory shortage and "re-allocation and
move" may require to allocate new page. Then, kick() should use GFP_ATOMIC if
they want to do reallocation. Right ?

Thanks,
-Kame

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Re: [patch 06/17] SLUB: Slab defrag core

[Christoph Lameter]

On Thu, 15 Nov 2007, KAMEZAWA Hiroyuki wrote:

> > 	from the partial list. So there could be a double effect.
> > 
> 
> I think shrink_slab()? is called under memory shortage and "re-allocation and
> move" may require to allocate new page. Then, kick() should use GFP_ATOMIC if
> they want to do reallocation. Right ?

There is no reason for allocating a new page. We are talking about slab 
allocations. The defrag stuff is run when there is a high degree of 
fragmentation. So there are a lot of partially allocated pages around. The 
allocation will grab a free object out of one of them.

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Re: [patch 06/17] SLUB: Slab defrag core

[KAMEZAWA Hiroyuki]

On Wed, 14 Nov 2007 17:28:24 -0800 (PST)
Christoph Lameter <clameter@sgi.com> wrote:

> On Thu, 15 Nov 2007, KAMEZAWA Hiroyuki wrote:
> 
> > > 	from the partial list. So there could be a double effect.
> > > 
> > 
> > I think shrink_slab()? is called under memory shortage and "re-allocation and
> > move" may require to allocate new page. Then, kick() should use GFP_ATOMIC if
> > they want to do reallocation. Right ?
> 
> There is no reason for allocating a new page. We are talking about slab 
> allocations. The defrag stuff is run when there is a high degree of 
> fragmentation. So there are a lot of partially allocated pages around. The 
> allocation will grab a free object out of one of them.
> 
Hmm, how about alloc_scratch() ?

BTW, how about counting succesfull kick() in __count_vm_events() and
the number of successfully defragmented pages ? (as a debug ops.)

I can't see how many dentrycache/inode defragment reaps objects after
shrinker()s.

Thanks,
-Kame

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Re: [patch 06/17] SLUB: Slab defrag core

[Christoph Lameter]

On Thu, 15 Nov 2007, KAMEZAWA Hiroyuki wrote:

> > There is no reason for allocating a new page. We are talking about slab 
> > allocations. The defrag stuff is run when there is a high degree of 
> > fragmentation. So there are a lot of partially allocated pages around. The 
> > allocation will grab a free object out of one of them.
> > 
> Hmm, how about alloc_scratch() ?

Hmmm.. We would need GFP_FAIL to simply fail on any attempt to get into 
the page allocator. __GFP_NOMEMALLOC could be sufficient.

> BTW, how about counting succesfull kick() in __count_vm_events() and
> the number of successfully defragmented pages ? (as a debug ops.)

Yes would be easy to add.

> I can't see how many dentrycache/inode defragment reaps objects after
> shrinker()s.

I typically do

	slabinfo -D

to observe the effect. I also have a debug patch here that we could add 
to see numbers in the syslog.

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[patch 06/17] SLUB: Slab defrag core

[Christoph Lameter]

[-- Attachment #1: 0052-SLUB-Slab-defrag-core.patch --]
[-- Type: text/plain, Size: 14495 bytes --]

Slab defragmentation may occur:

1. Unconditionally when kmem_cache_shrink is called on a slab cache by the
   kernel calling kmem_cache_shrink.

2. Use of the slabinfo command line to trigger slab shrinking.

3. Per node defrag conditionally when kmem_cache_defrag(<node>) is called.

   Defragmentation is only performed if the fragmentation of the slab
   is lower than the specified percentage. Fragmentation ratios are measured
   by calculating the percentage of objects in use compared to the total
   number of objects that the slab cache could hold without extending it.

   kmem_cache_defrag() takes a node parameter. This can either be -1 if
   defragmentation should be performed on all nodes, or a node number.
   If a node number was specified then defragmentation is only performed
   on a specific node.

   Slab defragmentation is a memory intensive operation that can be
   sped up in a NUMA system if mostly node local memory is accessed. It is
   possible to run shrinking on a node after execution of shrink_slabs().

A couple of functions must be setup via a call to kmem_cache_setup_defrag()
in order for a slabcache to support defragmentation. These are

void *get(struct kmem_cache *s, int nr, void **objects)

	Must obtain a reference to the listed objects. SLUB guarantees that
	the objects are still allocated. However, other threads may be blocked
	in slab_free() attempting to free objects in the slab. These may succeed
	as soon as get() returns to the slab allocator. The function must
	be able to detect such situations and void the attempts to free such
	objects (by for example voiding the corresponding entry in the objects
	array).

	No slab operations may be performed in get(). Interrupts
	are disabled. What can be done is very limited. The slab lock
	for the page that contains the object is taken. Any attempt to perform
	a slab operation may lead to a deadlock.

	get() returns a private pointer that is passed to kick. Should we
	be unable to obtain all references then that pointer may indicate
	to the kick() function that it should not attempt any object removal
	or move but simply remove the reference counts.

void kick(struct kmem_cache *, int nr, void **objects, void *get_result)

	After SLUB has established references to the objects in a
	slab it will then drop all locks and use kick() to move objects out
	of the slab. The existence of the object is guaranteed by virtue of
	the earlier obtained references via get(). The callback may perform
	any slab operation since no locks are held at the time of call.

	The callback should remove the object from the slab in some way. This
	may be accomplished by reclaiming the object and then running
	kmem_cache_free() or reallocating it and then running
	kmem_cache_free(). Reallocation is advantageous because the partial
	slabs were just sorted to have the partial slabs with the most objects
	first. Reallocation is likely to result in filling up a slab in
	addition to freeing up one slab. A filled up slab can also be removed
	from the partial list. So there could be a double effect.

	Kick() does not return a result. SLUB will check the number of
	remaining objects in the slab. If all objects were removed then
	we know that the operation was successful.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 include/linux/slab_def.h |    1 
 include/linux/slob_def.h |    1 
 include/linux/slub_def.h |    1 
 mm/slub.c                |  273 +++++++++++++++++++++++++++++++++++++----------
 4 files changed, 218 insertions(+), 58 deletions(-)

Index: linux-2.6.24-rc2-mm1/mm/slub.c
===================================================================
--- linux-2.6.24-rc2-mm1.orig/mm/slub.c	2007-11-14 13:39:56.920538689 -0800
+++ linux-2.6.24-rc2-mm1/mm/slub.c	2007-11-14 13:54:06.778195430 -0800
@@ -143,14 +143,14 @@
  * Mininum number of partial slabs. These will be left on the partial
  * lists even if they are empty. kmem_cache_shrink may reclaim them.
  */
-#define MIN_PARTIAL 2
+#define MIN_PARTIAL 5
 
 /*
  * Maximum number of desirable partial slabs.
- * The existence of more partial slabs makes kmem_cache_shrink
- * sort the partial list by the number of objects in the.
+ * More slabs cause kmem_cache_shrink to sort the slabs by objects
+ * and triggers slab defragmentation.
  */
-#define MAX_PARTIAL 10
+#define MAX_PARTIAL 20
 
 #define DEBUG_DEFAULT_FLAGS (SLAB_DEBUG_FREE | SLAB_RED_ZONE | \
 				SLAB_POISON | SLAB_STORE_USER)
@@ -2802,80 +2802,237 @@ static unsigned long count_partial(struc
 	return x;
 }
 
+ /*
+ * Vacate all objects in the given slab.
+  *
+ * The scratch aread passed to list function is sufficient to hold
+ * struct listhead times objects per slab. We use it to hold void ** times
+ * objects per slab plus a bitmap for each object.
+*/
+static int kmem_cache_vacate(struct page *page, void *scratch)
+{
+	void **vector = scratch;
+	void *p;
+	void *addr = page_address(page);
+	struct kmem_cache *s;
+	unsigned long *map;
+	int leftover;
+	int objects;
+	void *private;
+	unsigned long flags;
+	unsigned long state;
+
+	BUG_ON(!PageSlab(page));
+	local_irq_save(flags);
+	state = slab_lock(page);
+	BUG_ON(!(state & FROZEN));
+
+	s = page->slab;
+	map = scratch + max_defrag_slab_objects * sizeof(void **);
+	if (!page->inuse || !s->kick)
+		goto out;
+
+	/* Determine used objects */
+	bitmap_fill(map, s->objects);
+	for_each_free_object(p, s, page->freelist)
+			__clear_bit(slab_index(p, s, addr), map);
+
+	objects = 0;
+	memset(vector, 0, s->objects * sizeof(void **));
+	for_each_object(p, s, addr)
+		if (test_bit(slab_index(p, s, addr), map))
+			vector[objects++] = p;
+
+	private = s->get(s, objects, vector);
+
+	/*
+	 * Got references. Now we can drop the slab lock. The slab
+	 * is frozen so it cannot vanish from under us nor will
+	 * allocations be performed on the slab. However, unlocking the
+	 * slab will allow concurrent slab_frees to proceed.
+	 */
+	slab_unlock(page, state);
+	local_irq_restore(flags);
+
+	/*
+	 * Perform the KICK callbacks to remove the objects.
+	 */
+	s->kick(s, objects, vector, private);
+
+	local_irq_save(flags);
+	state = slab_lock(page);
+out:
+	/*
+	 * Check the result and unfreeze the slab
+	 */
+	leftover = page->inuse;
+	unfreeze_slab(s, page, leftover > 0, state);
+	local_irq_restore(flags);
+	return leftover;
+}
+
 /*
- * kmem_cache_shrink removes empty slabs from the partial lists and sorts
- * the remaining slabs by the number of items in use. The slabs with the
- * most items in use come first. New allocations will then fill those up
- * and thus they can be removed from the partial lists.
- *
- * The slabs with the least items are placed last. This results in them
- * being allocated from last increasing the chance that the last objects
- * are freed in them.
+ * Remove objects from a list of slab pages that have been gathered.
+ * Must be called with slabs that have been isolated before.
  */
-int kmem_cache_shrink(struct kmem_cache *s)
+int kmem_cache_reclaim(struct list_head *zaplist)
 {
-	int node;
-	int i;
-	struct kmem_cache_node *n;
+	int freed = 0;
+	void **scratch;
 	struct page *page;
-	struct page *t;
-	struct list_head *slabs_by_inuse =
-		kmalloc(sizeof(struct list_head) * s->objects, GFP_KERNEL);
-	unsigned long flags;
-	unsigned long state;
+	struct page *page2;
 
-	if (!slabs_by_inuse)
-		return -ENOMEM;
+	if (list_empty(zaplist))
+		return 0;
 
-	flush_all(s);
-	for_each_node_state(node, N_NORMAL_MEMORY) {
-		n = get_node(s, node);
+	scratch = alloc_scratch();
+	if (!scratch)
+		return 0;
 
-		if (!n->nr_partial)
-			continue;
+	list_for_each_entry_safe(page, page2, zaplist, lru) {
+		list_del(&page->lru);
+		if (kmem_cache_vacate(page, scratch) == 0)
+				freed++;
+	}
+	kfree(scratch);
+	return freed;
+}
 
-		for (i = 0; i < s->objects; i++)
-			INIT_LIST_HEAD(slabs_by_inuse + i);
+/*
+ * Shrink the slab cache on a particular node of the cache
+ * by releasing slabs with zero objects and trying to reclaim
+ * slabs with less than a quarter of objects allocated.
+ */
+static unsigned long __kmem_cache_shrink(struct kmem_cache *s,
+	struct kmem_cache_node *n)
+{
+	unsigned long flags;
+	struct page *page, *page2;
+	LIST_HEAD(zaplist);
+	int freed = 0;
+	unsigned long state;
 
-		spin_lock_irqsave(&n->list_lock, flags);
+	spin_lock_irqsave(&n->list_lock, flags);
+	list_for_each_entry_safe(page, page2, &n->partial, lru) {
+		if (page->inuse > s->objects / 4)
+			continue;
+		state = slab_trylock(page);
+		if (!state)
+			continue;
 
-		/*
-		 * Build lists indexed by the items in use in each slab.
-		 *
-		 * Note that concurrent frees may occur while we hold the
-		 * list_lock. page->inuse here is the upper limit.
-		 */
-		list_for_each_entry_safe(page, t, &n->partial, lru) {
-			if (page->inuse) {
-				list_move(&page->lru,
-				slabs_by_inuse + page->inuse);
-				continue;
+		if (page->inuse) {
+
+			list_move(&page->lru, &zaplist);
+			if (s->kick) {
+				n->nr_partial--;
+				state |= FROZEN;
 			}
-			state = slab_trylock(page);
-			if (!state)
-				continue;
-			/*
-			 * Must hold slab lock here because slab_free may have
-			 * freed the last object and be waiting to release the
-			 * slab.
-			 */
+			slab_unlock(page, state);
+
+		} else {
 			list_del(&page->lru);
 			n->nr_partial--;
 			slab_unlock(page, state);
 			discard_slab(s, page);
+			freed++;
 		}
+	}
 
-		/*
-		 * Rebuild the partial list with the slabs filled up most
-		 * first and the least used slabs at the end.
-		 */
-		for (i = s->objects - 1; i >= 0; i--)
-			list_splice(slabs_by_inuse + i, n->partial.prev);
+	if (!s->kick)
+		/* Simply put the zaplist at the end */
+		list_splice(&zaplist, n->partial.prev);
 
-		spin_unlock_irqrestore(&n->list_lock, flags);
+	spin_unlock_irqrestore(&n->list_lock, flags);
+
+	if (s->kick)
+		freed += kmem_cache_reclaim(&zaplist);
+	return freed;
+}
+
+static unsigned long __kmem_cache_defrag(struct kmem_cache *s, int node)
+{
+	unsigned long capacity;
+	unsigned long objects_in_full_slabs;
+	unsigned long ratio;
+	struct kmem_cache_node *n = get_node(s, node);
+
+	/*
+	 * An insignificant number of partial slabs means that the
+	 * slab cache does not need any defragmentation.
+	 */
+	if (n->nr_partial <= MAX_PARTIAL)
+		return 0;
+
+	capacity = atomic_long_read(&n->nr_slabs) * s->objects;
+	objects_in_full_slabs =
+			(atomic_long_read(&n->nr_slabs) - n->nr_partial)
+							* s->objects;
+	/*
+	 * Worst case calculation: If we would be over the ratio
+	 * even if all partial slabs would only have one object
+	 * then we can skip the next test that requires a scan
+	 * through all the partial page structs to sum up the actual
+	 * number of objects in the partial slabs.
+	 */
+	ratio = (objects_in_full_slabs + 1 * n->nr_partial) * 100 / capacity;
+	if (ratio > s->defrag_ratio)
+		return 0;
+
+	/*
+	 * Now for the real calculation. If usage ratio is more than required
+	 * then no defragmentation is necessary.
+	 */
+	ratio = (objects_in_full_slabs + count_partial(n)) * 100 / capacity;
+	if (ratio > s->defrag_ratio)
+		return 0;
+
+	return __kmem_cache_shrink(s, n) << s->order;
+}
+
+/*
+ * Defrag slabs conditional on the amount of fragmentation on each node.
+ */
+int kmem_cache_defrag(int node)
+{
+	struct kmem_cache *s;
+	unsigned long pages = 0;
+
+	/*
+	 * kmem_cache_defrag may be called from the reclaim path which may be
+	 * called for any page allocator alloc. So there is the danger that we
+	 * get called in a situation where slub already acquired the slub_lock
+	 * for other purposes.
+	 */
+	if (!down_read_trylock(&slub_lock))
+		return 0;
+
+	list_for_each_entry(s, &slab_caches, list) {
+		if (node == -1) {
+			int nid;
+
+			for_each_node_state(nid, N_NORMAL_MEMORY)
+				pages += __kmem_cache_defrag(s, nid);
+		} else
+			pages += __kmem_cache_defrag(s, node);
 	}
+	up_read(&slub_lock);
+	return pages;
+}
+EXPORT_SYMBOL(kmem_cache_defrag);
+
+/*
+ * kmem_cache_shrink removes empty slabs from the partial lists.
+ * If the slab cache support defragmentation then objects are
+ * reclaimed.
+ */
+int kmem_cache_shrink(struct kmem_cache *s)
+{
+	int node;
+
+	flush_all(s);
+	for_each_node_state(node, N_NORMAL_MEMORY)
+		__kmem_cache_shrink(s, get_node(s, node));
 
-	kfree(slabs_by_inuse);
 	return 0;
 }
 EXPORT_SYMBOL(kmem_cache_shrink);
Index: linux-2.6.24-rc2-mm1/include/linux/slab_def.h
===================================================================
--- linux-2.6.24-rc2-mm1.orig/include/linux/slab_def.h	2007-11-14 13:39:56.904538982 -0800
+++ linux-2.6.24-rc2-mm1/include/linux/slab_def.h	2007-11-14 13:39:56.936039109 -0800
@@ -101,5 +101,6 @@ ssize_t slabinfo_write(struct file *, co
 static inline void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private)) {}
+static inline int kmem_cache_defrag(int node) { return 0; }
 
 #endif	/* _LINUX_SLAB_DEF_H */
Index: linux-2.6.24-rc2-mm1/include/linux/slob_def.h
===================================================================
--- linux-2.6.24-rc2-mm1.orig/include/linux/slob_def.h	2007-11-14 13:39:56.904538982 -0800
+++ linux-2.6.24-rc2-mm1/include/linux/slob_def.h	2007-11-14 13:39:56.936039109 -0800
@@ -36,5 +36,6 @@ static inline void *__kmalloc(size_t siz
 static inline void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private)) {}
+static inline int kmem_cache_defrag(int node) { return 0; }
 
 #endif /* __LINUX_SLOB_DEF_H */
Index: linux-2.6.24-rc2-mm1/include/linux/slub_def.h
===================================================================
--- linux-2.6.24-rc2-mm1.orig/include/linux/slub_def.h	2007-11-14 13:39:56.900538713 -0800
+++ linux-2.6.24-rc2-mm1/include/linux/slub_def.h	2007-11-14 13:39:56.936039109 -0800
@@ -245,5 +245,6 @@ static __always_inline void *kmalloc_nod
 void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private));
+int kmem_cache_defrag(int node);
 
 #endif /* _LINUX_SLUB_DEF_H */

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[patch 00/17] Slab Fragmentation Reduction V10

[Christoph Lameter]

Slab fragmentation is mainly an issue if Linux is used as a fileserver
and large amounts of dentries, inodes and buffer heads accumulate. In some
load situations the slabs become very sparsely populated so that a lot of
memory is wasted by slabs that only contain one or a few objects. In
extreme cases the performance of a machine will become sluggish since
we are continually running reclaim. Slab defragmentation adds the
capability to recover the memory that is wasted.

The patchset can be pulled from and will be kept up to date at:

git://git.kernel.org/pub/scm/linux/kernel/git/christoph/vm.git slub-defrag

(Note that I will be on vacation till Feb 27th....)

Memory reclaim from the following slab caches is possible:

1. dentry cache
2. inode cache (with a generic interface to allow easy setup of more
   filesystems than the currently supported ext2/3/4 reiserfs, XFS
   and proc)
3. buffer_heads

One typical mechanism that triggers slab defragmentation on my systems
is the daily run of

	updatedb

Updatedb scans all files on the system which causes a high inode and dentry
use. After updatedb is complete we need to go back to the regular use
patterns (typical on my machine: kernel compiles). Those need the memory now
for different purposes. The inodes and dentries used for updatedb will
gradually be aged by the dentry/inode reclaim algorithm which will free
up the dentries and inode entries randomly through the slabs that were
allocated. As a result the slabs will become sparsely populated. If they
become empty then they can be freed but a lot of them will remain sparsely
populated. That is where slab defrag comes in: It removes the objects from
the slabs with just a few entries reclaiming more memory for other uses.
In the simplest case (as provided here) this is done by simply reclaiming
the objects.

However, if the logic in the kick() function is made more
sophisticated then we will be able to move the objects out of the slabs.
Allocations of objects is possible if a slab is fragmented without the use of
the page allocator because a large number of free slots are available. Moving
an object will reduce fragmentation in the slab the object is moved to.

V9->V10
- Rediff against upstream

V8->V9
- Rediff against 2.6.24-rc6-mm1

V7->V8
- Rediff against 2.6.24-rc3-mm2

V6->V7
- Rediff against 2.6.24-rc2-mm1
- Remove lumpy reclaim support. No point anymore given that the antifrag
  handling in 2.6.24-rc2 puts reclaimable slabs into different sections.
  Targeted reclaim never triggers. This has to wait until we make
  slabs movable or we need to perform a special version of lumpy reclaim
  in SLUB while we scan the partial lists for slabs to kick out.
  Removal simplifies handling significantly since we
  get to slabs in a more controlled way via the partial lists.
  The patchset now provides pure reduction of fragmentation levels.
- SLAB/SLOB: Provide inlines that do nothing
- Fix various smaller issues that were brought up during review of V6.

V5->V6
- Rediff against 2.6.24-rc2 + mm slub patches.
- Add reviewed by lines.
- Take out the experimental code to make slab pages movable. That
  has to wait until this has been considered by Mel.

V4->V5:
- Support lumpy reclaim for slabs
- Support reclaim via slab_shrink()
- Add constructors to insure a consistent object state at all times.

V3->V4:
- Optimize scan for slabs that need defragmentation
- Add /sys/slab/*/defrag_ratio to allow setting defrag limits
  per slab.
- Add support for buffer heads.
- Describe how the cleanup after the daily updatedb can be
  improved by slab defragmentation.

V2->V3
- Support directory reclaim
- Add infrastructure to trigger defragmentation after slab shrinking if we
  have slabs with a high degree of fragmentation.

V1->V2
- Clean up control flow using a state variable. Simplify API. Back to 2
  functions that now take arrays of objects.
- Inode defrag support for a set of filesystems
- Fix up dentry defrag support to work on negative dentries by adding
  a new dentry flag that indicates that a dentry is not in the process
  of being freed or allocated.

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[patch 01/17] SLUB: Extend slabinfo to support -D and -F options

[Christoph Lameter]

[-- Attachment #1: 0047-SLUB-Extend-slabinfo-to-support-D-and-C-options.patch --]
[-- Type: text/plain, Size: 6201 bytes --]

-F lists caches that support defragmentation

-C lists caches that use a ctor.

Change field names for defrag_ratio and remote_node_defrag_ratio.

Add determination of the allocation ratio for a slab. The allocation ratio
is the percentage of available slots for objects in use.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 Documentation/vm/slabinfo.c |   48 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 43 insertions(+), 5 deletions(-)

Index: linux-2.6/Documentation/vm/slabinfo.c
===================================================================
--- linux-2.6.orig/Documentation/vm/slabinfo.c	2008-02-14 15:18:49.077314846 -0800
+++ linux-2.6/Documentation/vm/slabinfo.c	2008-02-15 15:31:25.718359341 -0800
@@ -31,6 +31,8 @@ struct slabinfo {
 	int hwcache_align, object_size, objs_per_slab;
 	int sanity_checks, slab_size, store_user, trace;
 	int order, poison, reclaim_account, red_zone;
+	int defrag, ctor;
+	int defrag_ratio, remote_node_defrag_ratio;
 	unsigned long partial, objects, slabs;
 	unsigned long alloc_fastpath, alloc_slowpath;
 	unsigned long free_fastpath, free_slowpath;
@@ -64,6 +66,8 @@ int show_slab = 0;
 int skip_zero = 1;
 int show_numa = 0;
 int show_track = 0;
+int show_defrag = 0;
+int show_ctor = 0;
 int show_first_alias = 0;
 int validate = 0;
 int shrink = 0;
@@ -100,13 +104,15 @@ void fatal(const char *x, ...)
 void usage(void)
 {
 	printf("slabinfo 5/7/2007. (c) 2007 sgi. clameter@sgi.com\n\n"
-		"slabinfo [-ahnpvtsz] [-d debugopts] [slab-regexp]\n"
+		"slabinfo [-aCdDefFhnpvtsz] [-d debugopts] [slab-regexp]\n"
 		"-a|--aliases           Show aliases\n"
 		"-A|--activity          Most active slabs first\n"
+		"-C|--ctor              Show slabs with ctors\n"
 		"-d<options>|--debug=<options> Set/Clear Debug options\n"
 		"-D|--display-active    Switch line format to activity\n"
 		"-e|--empty             Show empty slabs\n"
 		"-f|--first-alias       Show first alias\n"
+		"-F|--defrag            Show defragmentable caches\n"
 		"-h|--help              Show usage information\n"
 		"-i|--inverted          Inverted list\n"
 		"-l|--slabs             Show slabs\n"
@@ -296,7 +302,7 @@ void first_line(void)
 		printf("Name                   Objects    Alloc     Free   %%Fast\n");
 	else
 		printf("Name                   Objects Objsize    Space "
-			"Slabs/Part/Cpu  O/S O %%Fr %%Ef Flg\n");
+			"Slabs/Part/Cpu  O/S O %%Ra %%Ef Flg\n");
 }
 
 /*
@@ -345,7 +351,7 @@ void slab_numa(struct slabinfo *s, int m
 		return;
 
 	if (!line) {
-		printf("\n%-21s:", mode ? "NUMA nodes" : "Slab");
+		printf("\n%-21s: Rto ", mode ? "NUMA nodes" : "Slab");
 		for(node = 0; node <= highest_node; node++)
 			printf(" %4d", node);
 		printf("\n----------------------");
@@ -354,6 +360,7 @@ void slab_numa(struct slabinfo *s, int m
 		printf("\n");
 	}
 	printf("%-21s ", mode ? "All slabs" : s->name);
+	printf("%3d ", s->remote_node_defrag_ratio);
 	for(node = 0; node <= highest_node; node++) {
 		char b[20];
 
@@ -492,6 +499,8 @@ void report(struct slabinfo *s)
 		printf("** Slabs are destroyed via RCU\n");
 	if (s->reclaim_account)
 		printf("** Reclaim accounting active\n");
+	if (s->defrag)
+		printf("** Defragmentation at %d%%\n", s->defrag_ratio);
 
 	printf("\nSizes (bytes)     Slabs              Debug                Memory\n");
 	printf("------------------------------------------------------------------------\n");
@@ -539,6 +548,12 @@ void slabcache(struct slabinfo *s)
 	if (show_empty && s->slabs)
 		return;
 
+	if (show_defrag && !s->defrag)
+		return;
+
+	if (show_ctor && !s->ctor)
+		return;
+
 	store_size(size_str, slab_size(s));
 	snprintf(dist_str, 40, "%lu/%lu/%d", s->slabs, s->partial, s->cpu_slabs);
 
@@ -549,6 +564,10 @@ void slabcache(struct slabinfo *s)
 		*p++ = '*';
 	if (s->cache_dma)
 		*p++ = 'd';
+	if (s->defrag)
+		*p++ = 'F';
+	if (s->ctor)
+		*p++ = 'C';
 	if (s->hwcache_align)
 		*p++ = 'A';
 	if (s->poison)
@@ -582,7 +601,8 @@ void slabcache(struct slabinfo *s)
 		printf("%-21s %8ld %7d %8s %14s %4d %1d %3ld %3ld %s\n",
 			s->name, s->objects, s->object_size, size_str, dist_str,
 			s->objs_per_slab, s->order,
-			s->slabs ? (s->partial * 100) / s->slabs : 100,
+			s->slabs ? (s->partial * 100) /
+					(s->slabs * s->objs_per_slab) : 100,
 			s->slabs ? (s->objects * s->object_size * 100) /
 				(s->slabs * (page_size << s->order)) : 100,
 			flags);
@@ -1193,7 +1213,17 @@ void read_slab_dir(void)
 			slab->deactivate_to_head = get_obj("deactivate_to_head");
 			slab->deactivate_to_tail = get_obj("deactivate_to_tail");
 			slab->deactivate_remote_frees = get_obj("deactivate_remote_frees");
+			slab->defrag_ratio = get_obj("defrag_ratio");
+			slab->remote_node_defrag_ratio =
+				get_obj("remote_node_defrag_ratio");
 			chdir("..");
+			if (read_slab_obj(slab, "ops")) {
+				if (strstr(buffer, "ctor :"))
+					slab->ctor = 1;
+				if (strstr(buffer, "kick :"))
+					slab->defrag = 1;
+			}
+
 			if (slab->name[0] == ':')
 				alias_targets++;
 			slab++;
@@ -1244,10 +1274,12 @@ void output_slabs(void)
 struct option opts[] = {
 	{ "aliases", 0, NULL, 'a' },
 	{ "activity", 0, NULL, 'A' },
+	{ "ctor", 0, NULL, 'C' },
 	{ "debug", 2, NULL, 'd' },
 	{ "display-activity", 0, NULL, 'D' },
 	{ "empty", 0, NULL, 'e' },
 	{ "first-alias", 0, NULL, 'f' },
+	{ "defrag", 0, NULL, 'F' },
 	{ "help", 0, NULL, 'h' },
 	{ "inverted", 0, NULL, 'i'},
 	{ "numa", 0, NULL, 'n' },
@@ -1270,7 +1302,7 @@ int main(int argc, char *argv[])
 
 	page_size = getpagesize();
 
-	while ((c = getopt_long(argc, argv, "aAd::Defhil1noprstvzTS",
+	while ((c = getopt_long(argc, argv, "aACd::DefFhil1noprstvzTS",
 						opts, NULL)) != -1)
 		switch (c) {
 		case '1':
@@ -1326,6 +1358,12 @@ int main(int argc, char *argv[])
 		case 'z':
 			skip_zero = 0;
 			break;
+		case 'C':
+			show_ctor = 1;
+			break;
+		case 'F':
+			show_defrag = 1;
+			break;
 		case 'T':
 			show_totals = 1;
 			break;

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[patch 02/17] SLUB: Add defrag_ratio field and sysfs support.

[Christoph Lameter]

[-- Attachment #1: 0048-SLUB-Add-defrag_ratio-field-and-sysfs-support.patch --]
[-- Type: text/plain, Size: 2835 bytes --]

The defrag_ratio is used to set the threshold at which defragmentation
should be run on a slabcache.

The allocation ratio is measured in the percentage of the available slots
allocated. The percentage will be lower for slabs that are more fragmented.

Add a defrag ratio field and set it to 30% by default. A limit of 30% specified
that less than 3 out of 10 available slots for objects are in use before
slab defragmeentation runs.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 include/linux/slub_def.h |    7 +++++++
 mm/slub.c                |   18 ++++++++++++++++++
 2 files changed, 25 insertions(+)

Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h	2008-02-15 15:22:22.064550321 -0800
+++ linux-2.6/include/linux/slub_def.h	2008-02-15 15:31:53.954427883 -0800
@@ -79,6 +79,13 @@ struct kmem_cache {
 	void (*ctor)(struct kmem_cache *, void *);
 	int inuse;		/* Offset to metadata */
 	int align;		/* Alignment */
+	int defrag_ratio;	/*
+				 * objects/possible-objects limit. If we have
+				 * less that the specified percentage of
+				 * objects allocated then defrag passes
+				 * will start to occur during reclaim.
+				 */
+
 	const char *name;	/* Name (only for display!) */
 	struct list_head list;	/* List of slab caches */
 #ifdef CONFIG_SLUB_DEBUG
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2008-02-15 15:22:22.884553646 -0800
+++ linux-2.6/mm/slub.c	2008-02-15 15:31:53.958427919 -0800
@@ -2395,6 +2395,7 @@ static int kmem_cache_open(struct kmem_c
 		goto error;
 
 	s->refcount = 1;
+	s->defrag_ratio = 30;
 #ifdef CONFIG_NUMA
 	s->remote_node_defrag_ratio = 100;
 #endif
@@ -4084,6 +4085,22 @@ static ssize_t free_calls_show(struct km
 }
 SLAB_ATTR_RO(free_calls);
 
+static ssize_t defrag_ratio_show(struct kmem_cache *s, char *buf)
+{
+	return sprintf(buf, "%d\n", s->defrag_ratio);
+}
+
+static ssize_t defrag_ratio_store(struct kmem_cache *s,
+				const char *buf, size_t length)
+{
+	int n = simple_strtoul(buf, NULL, 10);
+
+	if (n < 100)
+		s->defrag_ratio = n;
+	return length;
+}
+SLAB_ATTR(defrag_ratio);
+
 #ifdef CONFIG_NUMA
 static ssize_t remote_node_defrag_ratio_show(struct kmem_cache *s, char *buf)
 {
@@ -4184,6 +4201,7 @@ static struct attribute *slab_attrs[] = 
 	&shrink_attr.attr,
 	&alloc_calls_attr.attr,
 	&free_calls_attr.attr,
+	&defrag_ratio_attr.attr,
 #ifdef CONFIG_ZONE_DMA
 	&cache_dma_attr.attr,
 #endif

-- 

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[patch 03/17] SLUB: Replace ctor field with ops field in /sys/slab/*

[Christoph Lameter]

[-- Attachment #1: 0049-SLUB-Replace-ctor-field-with-ops-field-in-sys-slab.patch --]
[-- Type: text/plain, Size: 1663 bytes --]

Create an ops field in /sys/slab/*/ops to contain all the operations defined
on a slab. This will be used to display the additional operations that will
be defined soon.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 mm/slub.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2008-02-15 15:31:53.958427919 -0800
+++ linux-2.6/mm/slub.c	2008-02-15 15:32:00.654444198 -0800
@@ -3862,16 +3862,18 @@ static ssize_t order_show(struct kmem_ca
 }
 SLAB_ATTR(order);
 
-static ssize_t ctor_show(struct kmem_cache *s, char *buf)
+static ssize_t ops_show(struct kmem_cache *s, char *buf)
 {
-	if (s->ctor) {
-		int n = sprint_symbol(buf, (unsigned long)s->ctor);
+	int x = 0;
 
-		return n + sprintf(buf + n, "\n");
+	if (s->ctor) {
+		x += sprintf(buf + x, "ctor : ");
+		x += sprint_symbol(buf + x, (unsigned long)s->ops->ctor);
+		x += sprintf(buf + x, "\n");
 	}
-	return 0;
+	return x;
 }
-SLAB_ATTR_RO(ctor);
+SLAB_ATTR_RO(ops);
 
 static ssize_t aliases_show(struct kmem_cache *s, char *buf)
 {
@@ -4186,7 +4188,7 @@ static struct attribute *slab_attrs[] = 
 	&slabs_attr.attr,
 	&partial_attr.attr,
 	&cpu_slabs_attr.attr,
-	&ctor_attr.attr,
+	&ops_attr.attr,
 	&aliases_attr.attr,
 	&align_attr.attr,
 	&sanity_checks_attr.attr,

-- 

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[patch 04/17] SLUB: Add get() and kick() methods

[Christoph Lameter]

[-- Attachment #1: 0050-SLUB-Add-get-and-kick-methods.patch --]
[-- Type: text/plain, Size: 5416 bytes --]

Add the two methods needed for defragmentation and add the display of the
methods via the proc interface.

Add documentation explaining the use of these methods.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 include/linux/slab_def.h |    4 ++++
 include/linux/slob_def.h |    4 ++++
 include/linux/slub_def.h |   35 +++++++++++++++++++++++++++++++++++
 mm/slub.c                |   32 ++++++++++++++++++++++++++++++--
 4 files changed, 73 insertions(+), 2 deletions(-)

Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h	2008-02-15 16:38:21.753876823 -0800
+++ linux-2.6/include/linux/slub_def.h	2008-02-15 16:38:31.401917080 -0800
@@ -74,6 +74,37 @@ struct kmem_cache {
 	gfp_t allocflags;	/* gfp flags to use on each alloc */
 	int refcount;		/* Refcount for slab cache destroy */
 	void (*ctor)(struct kmem_cache *, void *);
+	/*
+	 * Called with slab lock held and interrupts disabled.
+	 * No slab operation may be performed in get().
+	 *
+	 * Parameters passed are the number of objects to process
+	 * and an array of pointers to objects for which we
+	 * need references.
+	 *
+	 * Returns a pointer that is passed to the kick function.
+	 * If all objects cannot be moved then the pointer may
+	 * indicate that this wont work and then kick can simply
+	 * remove the references that were already obtained.
+	 *
+	 * The array passed to get() is also passed to kick(). The
+	 * function may remove objects by setting array elements to NULL.
+	 */
+	void *(*get)(struct kmem_cache *, int nr, void **);
+
+	/*
+	 * Called with no locks held and interrupts enabled.
+	 * Any operation may be performed in kick().
+	 *
+	 * Parameters passed are the number of objects in the array,
+	 * the array of pointers to the objects and the pointer
+	 * returned by get().
+	 *
+	 * Success is checked by examining the number of remaining
+	 * objects in the slab.
+	 */
+	void (*kick)(struct kmem_cache *, int nr, void **, void *private);
+
 	int inuse;		/* Offset to metadata */
 	int align;		/* Alignment */
 	int defrag_ratio;	/*
@@ -238,4 +269,8 @@ static __always_inline void *kmalloc_nod
 }
 #endif
 
+void kmem_cache_setup_defrag(struct kmem_cache *s,
+	void *(*get)(struct kmem_cache *, int nr, void **),
+	void (*kick)(struct kmem_cache *, int nr, void **, void *private));
+
 #endif /* _LINUX_SLUB_DEF_H */
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2008-02-15 16:38:23.133882506 -0800
+++ linux-2.6/mm/slub.c	2008-02-15 16:39:19.946123239 -0800
@@ -2791,6 +2791,20 @@ void kfree(const void *x)
 }
 EXPORT_SYMBOL(kfree);
 
+void kmem_cache_setup_defrag(struct kmem_cache *s,
+	void *(*get)(struct kmem_cache *, int nr, void **),
+	void (*kick)(struct kmem_cache *, int nr, void **, void *private))
+{
+	/*
+	 * Defragmentable slabs must have a ctor otherwise objects may be
+	 * in an undetermined state after they are allocated.
+	 */
+	BUG_ON(!s->ctor);
+	s->get = get;
+	s->kick = kick;
+}
+EXPORT_SYMBOL(kmem_cache_setup_defrag);
+
 static unsigned long count_partial(struct kmem_cache_node *n)
 {
 	unsigned long flags;
@@ -3092,7 +3106,7 @@ static int slab_unmergeable(struct kmem_
 	if ((s->flags & __PAGE_ALLOC_FALLBACK))
 		return 1;
 
-	if (s->ctor)
+	if (s->ctor || s->kick || s->get)
 		return 1;
 
 	/*
@@ -3827,7 +3841,21 @@ static ssize_t ops_show(struct kmem_cach
 
 	if (s->ctor) {
 		x += sprintf(buf + x, "ctor : ");
-		x += sprint_symbol(buf + x, (unsigned long)s->ops->ctor);
+		x += sprint_symbol(buf + x, (unsigned long)s->ctor);
+		x += sprintf(buf + x, "\n");
+	}
+
+	if (s->get) {
+		x += sprintf(buf + x, "get : ");
+		x += sprint_symbol(buf + x,
+				(unsigned long)s->get);
+		x += sprintf(buf + x, "\n");
+	}
+
+	if (s->kick) {
+		x += sprintf(buf + x, "kick : ");
+		x += sprint_symbol(buf + x,
+				(unsigned long)s->kick);
 		x += sprintf(buf + x, "\n");
 	}
 	return x;
Index: linux-2.6/include/linux/slab_def.h
===================================================================
--- linux-2.6.orig/include/linux/slab_def.h	2008-02-15 16:34:53.392938232 -0800
+++ linux-2.6/include/linux/slab_def.h	2008-02-15 16:38:31.405917002 -0800
@@ -95,4 +95,8 @@ found:
 
 #endif	/* CONFIG_NUMA */
 
+static inline void kmem_cache_setup_defrag(struct kmem_cache *s,
+	void *(*get)(struct kmem_cache *, int nr, void **),
+	void (*kick)(struct kmem_cache *, int nr, void **, void *private)) {}
+
 #endif	/* _LINUX_SLAB_DEF_H */
Index: linux-2.6/include/linux/slob_def.h
===================================================================
--- linux-2.6.orig/include/linux/slob_def.h	2008-02-15 16:34:53.392938232 -0800
+++ linux-2.6/include/linux/slob_def.h	2008-02-15 16:38:31.405917002 -0800
@@ -33,4 +33,8 @@ static inline void *__kmalloc(size_t siz
 	return kmalloc(size, flags);
 }
 
+static inline void kmem_cache_setup_defrag(struct kmem_cache *s,
+	void *(*get)(struct kmem_cache *, int nr, void **),
+	void (*kick)(struct kmem_cache *, int nr, void **, void *private)) {}
+
 #endif /* __LINUX_SLOB_DEF_H */

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[patch 05/17] SLUB: Sort slab cache list and establish maximum objects for defrag slabs

[Christoph Lameter]

[-- Attachment #1: 0051-SLUB-Sort-slab-cache-list-and-establish-maximum-obj.patch --]
[-- Type: text/plain, Size: 2621 bytes --]

When defragmenting slabs then it is advantageous to have all
defragmentable slabs together at the beginning of the list so that there is
no need to scan the complete list. Put defragmentable caches first when adding
a slab cache and others last.

Determine the maximum number of objects in defragmentable slabs. This allows
to size the allocation of arrays holding refs to these objects later.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 mm/slub.c |   19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2008-02-15 16:39:19.946123239 -0800
+++ linux-2.6/mm/slub.c	2008-02-15 16:39:24.198141417 -0800
@@ -236,6 +236,9 @@ static enum {
 static DECLARE_RWSEM(slub_lock);
 static LIST_HEAD(slab_caches);
 
+/* Maximum objects in defragmentable slabs */
+static unsigned int max_defrag_slab_objects = 0;
+
 /*
  * Tracking user of a slab.
  */
@@ -2573,7 +2576,7 @@ static struct kmem_cache *create_kmalloc
 			flags | __KMALLOC_CACHE, NULL))
 		goto panic;
 
-	list_add(&s->list, &slab_caches);
+	list_add_tail(&s->list, &slab_caches);
 	up_write(&slub_lock);
 	if (sysfs_slab_add(s))
 		goto panic;
@@ -2791,6 +2794,13 @@ void kfree(const void *x)
 }
 EXPORT_SYMBOL(kfree);
 
+static inline void *alloc_scratch(void)
+{
+	return kmalloc(max_defrag_slab_objects * sizeof(void *) +
+	    BITS_TO_LONGS(max_defrag_slab_objects) * sizeof(unsigned long),
+								GFP_KERNEL);
+}
+
 void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private))
@@ -2802,6 +2812,11 @@ void kmem_cache_setup_defrag(struct kmem
 	BUG_ON(!s->ctor);
 	s->get = get;
 	s->kick = kick;
+	down_write(&slub_lock);
+	list_move(&s->list, &slab_caches);
+	if (s->objects > max_defrag_slab_objects)
+		max_defrag_slab_objects = s->objects;
+	up_write(&slub_lock);
 }
 EXPORT_SYMBOL(kmem_cache_setup_defrag);
 
@@ -3193,7 +3208,7 @@ struct kmem_cache *kmem_cache_create(con
 	if (s) {
 		if (kmem_cache_open(s, GFP_KERNEL, name,
 				size, align, flags, ctor)) {
-			list_add(&s->list, &slab_caches);
+			list_add_tail(&s->list, &slab_caches);
 			up_write(&slub_lock);
 			if (sysfs_slab_add(s))
 				goto err;

-- 

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[patch 06/17] SLUB: Slab defrag core

[Christoph Lameter]

[-- Attachment #1: 0052-SLUB-Slab-defrag-core.patch --]
[-- Type: text/plain, Size: 14131 bytes --]

Slab defragmentation may occur:

1. Unconditionally when kmem_cache_shrink is called on a slab cache by the
   kernel calling kmem_cache_shrink.

2. Use of the slabinfo command line to trigger slab shrinking.

3. Per node defrag conditionally when kmem_cache_defrag(<node>) is called.

   Defragmentation is only performed if the fragmentation of the slab
   is lower than the specified percentage. Fragmentation ratios are measured
   by calculating the percentage of objects in use compared to the total
   number of objects that the slab cache could hold without extending it.

   kmem_cache_defrag() takes a node parameter. This can either be -1 if
   defragmentation should be performed on all nodes, or a node number.
   If a node number was specified then defragmentation is only performed
   on a specific node.

   Slab defragmentation is a memory intensive operation that can be
   sped up in a NUMA system if mostly node local memory is accessed. It is
   possible to run shrinking on a node after execution of shrink_slabs().

A couple of functions must be setup via a call to kmem_cache_setup_defrag()
in order for a slabcache to support defragmentation. These are

void *get(struct kmem_cache *s, int nr, void **objects)

	Must obtain a reference to the listed objects. SLUB guarantees that
	the objects are still allocated. However, other threads may be blocked
	in slab_free() attempting to free objects in the slab. These may succeed
	as soon as get() returns to the slab allocator. The function must
	be able to detect such situations and void the attempts to free such
	objects (by for example voiding the corresponding entry in the objects
	array).

	No slab operations may be performed in get(). Interrupts
	are disabled. What can be done is very limited. The slab lock
	for the page that contains the object is taken. Any attempt to perform
	a slab operation may lead to a deadlock.

	get() returns a private pointer that is passed to kick. Should we
	be unable to obtain all references then that pointer may indicate
	to the kick() function that it should not attempt any object removal
	or move but simply remove the reference counts.

void kick(struct kmem_cache *, int nr, void **objects, void *get_result)

	After SLUB has established references to the objects in a
	slab it will then drop all locks and use kick() to move objects out
	of the slab. The existence of the object is guaranteed by virtue of
	the earlier obtained references via get(). The callback may perform
	any slab operation since no locks are held at the time of call.

	The callback should remove the object from the slab in some way. This
	may be accomplished by reclaiming the object and then running
	kmem_cache_free() or reallocating it and then running
	kmem_cache_free(). Reallocation is advantageous because the partial
	slabs were just sorted to have the partial slabs with the most objects
	first. Reallocation is likely to result in filling up a slab in
	addition to freeing up one slab. A filled up slab can also be removed
	from the partial list. So there could be a double effect.

	Kick() does not return a result. SLUB will check the number of
	remaining objects in the slab. If all objects were removed then
	we know that the operation was successful.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 include/linux/slab_def.h |    1 
 include/linux/slob_def.h |    1 
 include/linux/slub_def.h |    1 
 mm/slub.c                |  274 +++++++++++++++++++++++++++++++++++++----------
 4 files changed, 220 insertions(+), 57 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2008-02-15 16:39:24.198141417 -0800
+++ linux-2.6/mm/slub.c	2008-02-15 16:41:07.606611300 -0800
@@ -183,10 +183,10 @@ static inline void ClearSlabDebug(struct
 
 /*
  * Maximum number of desirable partial slabs.
- * The existence of more partial slabs makes kmem_cache_shrink
- * sort the partial list by the number of objects in the.
+ * More slabs cause kmem_cache_shrink to sort the slabs by objects
+ * and triggers slab defragmentation.
  */
-#define MAX_PARTIAL 10
+#define MAX_PARTIAL 20
 
 #define DEBUG_DEFAULT_FLAGS (SLAB_DEBUG_FREE | SLAB_RED_ZONE | \
 				SLAB_POISON | SLAB_STORE_USER)
@@ -2834,76 +2834,236 @@ static unsigned long count_partial(struc
 }
 
 /*
- * kmem_cache_shrink removes empty slabs from the partial lists and sorts
- * the remaining slabs by the number of items in use. The slabs with the
- * most items in use come first. New allocations will then fill those up
- * and thus they can be removed from the partial lists.
+ * Vacate all objects in the given slab.
  *
- * The slabs with the least items are placed last. This results in them
- * being allocated from last increasing the chance that the last objects
- * are freed in them.
+ * The scratch aread passed to list function is sufficient to hold
+ * struct listhead times objects per slab. We use it to hold void ** times
+ * objects per slab plus a bitmap for each object.
  */
-int kmem_cache_shrink(struct kmem_cache *s)
+static int kmem_cache_vacate(struct page *page, void *scratch)
 {
-	int node;
-	int i;
-	struct kmem_cache_node *n;
-	struct page *page;
-	struct page *t;
-	struct list_head *slabs_by_inuse =
-		kmalloc(sizeof(struct list_head) * s->objects, GFP_KERNEL);
+	void **vector = scratch;
+	void *p;
+	void *addr = page_address(page);
+	struct kmem_cache *s;
+	unsigned long *map;
+	int leftover;
+	int count;
+	void *private;
 	unsigned long flags;
+	unsigned long objects;
 
-	if (!slabs_by_inuse)
-		return -ENOMEM;
+	BUG_ON(!PageSlab(page));
+	local_irq_save(flags);
+	slab_lock(page);
+	BUG_ON(!SlabFrozen(page));
 
-	flush_all(s);
-	for_each_node_state(node, N_NORMAL_MEMORY) {
-		n = get_node(s, node);
+	s = page->slab;
+	objects = s->objects;
+	map = scratch + max_defrag_slab_objects * sizeof(void **);
+	if (!page->inuse || !s->kick)
+		goto out;
 
-		if (!n->nr_partial)
-			continue;
+	/* Determine used objects */
+	bitmap_fill(map, objects);
+	for_each_free_object(p, s, page->freelist)
+		__clear_bit(slab_index(p, s, addr), map);
 
-		for (i = 0; i < s->objects; i++)
-			INIT_LIST_HEAD(slabs_by_inuse + i);
+	count = 0;
+	memset(vector, 0, objects * sizeof(void **));
+	for_each_object(p, s, addr)
+		if (test_bit(slab_index(p, s, addr), map))
+			vector[count++] = p;
 
-		spin_lock_irqsave(&n->list_lock, flags);
+	private = s->get(s, count, vector);
 
-		/*
-		 * Build lists indexed by the items in use in each slab.
-		 *
-		 * Note that concurrent frees may occur while we hold the
-		 * list_lock. page->inuse here is the upper limit.
-		 */
-		list_for_each_entry_safe(page, t, &n->partial, lru) {
-			if (!page->inuse && slab_trylock(page)) {
-				/*
-				 * Must hold slab lock here because slab_free
-				 * may have freed the last object and be
-				 * waiting to release the slab.
-				 */
-				list_del(&page->lru);
+	/*
+	 * Got references. Now we can drop the slab lock. The slab
+	 * is frozen so it cannot vanish from under us nor will
+	 * allocations be performed on the slab. However, unlocking the
+	 * slab will allow concurrent slab_frees to proceed.
+	 */
+	slab_unlock(page);
+	local_irq_restore(flags);
+
+	/*
+	 * Perform the KICK callbacks to remove the objects.
+	 */
+	s->kick(s, count, vector, private);
+
+	local_irq_save(flags);
+	slab_lock(page);
+out:
+	/*
+	 * Check the result and unfreeze the slab
+	 */
+	leftover = page->inuse;
+	unfreeze_slab(s, page, leftover > 0);
+	local_irq_restore(flags);
+	return leftover;
+}
+
+/*
+ * Remove objects from a list of slab pages that have been gathered.
+ * Must be called with slabs that have been isolated before.
+ */
+int kmem_cache_reclaim(struct list_head *zaplist)
+{
+	int freed = 0;
+	void **scratch;
+ 	struct page *page;
+	struct page *page2;
+
+	if (list_empty(zaplist))
+		return 0;
+
+	scratch = alloc_scratch();
+	if (!scratch)
+		return 0;
+
+	list_for_each_entry_safe(page, page2, zaplist, lru) {
+		list_del(&page->lru);
+		if (kmem_cache_vacate(page, scratch) == 0)
+				freed++;
+	}
+	kfree(scratch);
+	return freed;
+}
+
+/*
+ * Shrink the slab cache on a particular node of the cache
+ * by releasing slabs with zero objects and trying to reclaim
+ * slabs with less than a quarter of objects allocated.
+ */
+static unsigned long __kmem_cache_shrink(struct kmem_cache *s,
+	struct kmem_cache_node *n)
+{
+	unsigned long flags;
+	struct page *page, *page2;
+	LIST_HEAD(zaplist);
+	int freed = 0;
+
+	spin_lock_irqsave(&n->list_lock, flags);
+	list_for_each_entry_safe(page, page2, &n->partial, lru) {
+		if (page->inuse > s->objects / 4)
+			continue;
+		if (!slab_trylock(page))
+			continue;
+
+		if (page->inuse) {
+
+			list_move(&page->lru, &zaplist);
+			if (s->kick) {
 				n->nr_partial--;
-				slab_unlock(page);
-				discard_slab(s, page);
-			} else {
-				list_move(&page->lru,
-				slabs_by_inuse + page->inuse);
-			}
+				SetSlabFrozen(page);
+ 			}
+			slab_unlock(page);
+
+		} else {
+ 			list_del(&page->lru);
+ 			n->nr_partial--;
+ 			slab_unlock(page);
+ 			discard_slab(s, page);
+			freed++;
 		}
+	}
 
-		/*
-		 * Rebuild the partial list with the slabs filled up most
-		 * first and the least used slabs at the end.
-		 */
-		for (i = s->objects - 1; i >= 0; i--)
-			list_splice(slabs_by_inuse + i, n->partial.prev);
+	if (!s->kick)
+		/* Simply put the zaplist at the end */
+		list_splice(&zaplist, n->partial.prev);
 
-		spin_unlock_irqrestore(&n->list_lock, flags);
+	spin_unlock_irqrestore(&n->list_lock, flags);
+
+	if (s->kick)
+		freed += kmem_cache_reclaim(&zaplist);
+	return freed;
+}
+
+static unsigned long __kmem_cache_defrag(struct kmem_cache *s, int node)
+{
+	unsigned long capacity;
+	unsigned long objects_in_full_slabs;
+	unsigned long ratio;
+	struct kmem_cache_node *n = get_node(s, node);
+
+	/*
+	 * An insignificant number of partial slabs means that the
+	 * slab cache does not need any defragmentation.
+	 */
+	if (n->nr_partial <= MAX_PARTIAL)
+		return 0;
+
+	capacity = atomic_long_read(&n->nr_slabs) * s->objects;
+	objects_in_full_slabs =
+			(atomic_long_read(&n->nr_slabs) - n->nr_partial)
+							* s->objects;
+	/*
+	 * Worst case calculation: If we would be over the ratio
+	 * even if all partial slabs would only have one object
+	 * then we can skip the next test that requires a scan
+	 * through all the partial page structs to sum up the actual
+	 * number of objects in the partial slabs.
+	 */
+	ratio = (objects_in_full_slabs + 1 * n->nr_partial) * 100 / capacity;
+	if (ratio > s->defrag_ratio)
+		return 0;
+
+	/*
+	 * Now for the real calculation. If usage ratio is more than required
+	 * then no defragmentation is necessary.
+	 */
+	ratio = (objects_in_full_slabs + count_partial(n)) * 100 / capacity;
+	if (ratio > s->defrag_ratio)
+		return 0;
+
+	return __kmem_cache_shrink(s, n) << s->order;
+}
+
+/*
+ * Defrag slabs conditional on the amount of fragmentation on each node.
+ */
+int kmem_cache_defrag(int node)
+{
+	struct kmem_cache *s;
+	unsigned long pages = 0;
+
+	/*
+	 * kmem_cache_defrag may be called from the reclaim path which may be
+	 * called for any page allocator alloc. So there is the danger that we
+	 * get called in a situation where slub already acquired the slub_lock
+	 * for other purposes.
+	 */
+	if (!down_read_trylock(&slub_lock))
+		return 0;
+
+	list_for_each_entry(s, &slab_caches, list) {
+		if (node == -1) {
+			int nid;
+
+			for_each_node_state(nid, N_NORMAL_MEMORY)
+				pages += __kmem_cache_defrag(s, nid);
+		} else
+			pages += __kmem_cache_defrag(s, node);
 	}
+	up_read(&slub_lock);
+	return pages;
+}
+EXPORT_SYMBOL(kmem_cache_defrag);
 
-	kfree(slabs_by_inuse);
-	return 0;
+/*
+ * kmem_cache_shrink removes empty slabs from the partial lists.
+ * If the slab cache support defragmentation then objects are
+ * reclaimed.
+ */
+int kmem_cache_shrink(struct kmem_cache *s)
+{
+	int node;
+
+	flush_all(s);
+	for_each_node_state(node, N_NORMAL_MEMORY)
+		__kmem_cache_shrink(s, get_node(s, node));
+
+ 	return 0;
 }
 EXPORT_SYMBOL(kmem_cache_shrink);
 
Index: linux-2.6/include/linux/slab_def.h
===================================================================
--- linux-2.6.orig/include/linux/slab_def.h	2008-02-15 16:38:31.405917002 -0800
+++ linux-2.6/include/linux/slab_def.h	2008-02-15 16:39:28.526160097 -0800
@@ -98,5 +98,6 @@ found:
 static inline void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private)) {}
+static inline int kmem_cache_defrag(int node) { return 0; }
 
 #endif	/* _LINUX_SLAB_DEF_H */
Index: linux-2.6/include/linux/slob_def.h
===================================================================
--- linux-2.6.orig/include/linux/slob_def.h	2008-02-15 16:38:31.405917002 -0800
+++ linux-2.6/include/linux/slob_def.h	2008-02-15 16:39:28.526160097 -0800
@@ -36,5 +36,6 @@ static inline void *__kmalloc(size_t siz
 static inline void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private)) {}
+static inline int kmem_cache_defrag(int node) { return 0; }
 
 #endif /* __LINUX_SLOB_DEF_H */
Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h	2008-02-15 16:38:31.401917080 -0800
+++ linux-2.6/include/linux/slub_def.h	2008-02-15 16:39:28.526160097 -0800
@@ -272,5 +272,6 @@ static __always_inline void *kmalloc_nod
 void kmem_cache_setup_defrag(struct kmem_cache *s,
 	void *(*get)(struct kmem_cache *, int nr, void **),
 	void (*kick)(struct kmem_cache *, int nr, void **, void *private));
+int kmem_cache_defrag(int node);
 
 #endif /* _LINUX_SLUB_DEF_H */

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[patch 07/17] SLUB: Add KICKABLE to avoid repeated kick() attempts

[Christoph Lameter]

[-- Attachment #1: 0064-SLUB-Add-SlabReclaimable-to-avoid-repeated-reclai.patch --]
[-- Type: text/plain, Size: 3126 bytes --]

Add a flag KICKABLE to be set on slabs with a defragmentation method

Clear the flag if a kick action is not successful in reducing the
number of objects in a slab.

The KICKABLE flag is set again when all objeccts of the slab have been
allocated and it is removed from the partial lists.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 mm/slub.c |   28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2008-02-15 16:41:07.606611300 -0800
+++ linux-2.6/mm/slub.c	2008-02-15 16:41:42.806805718 -0800
@@ -101,6 +101,7 @@
  */
 
 #define FROZEN (1 << PG_active)
+#define KICKABLE (1 << PG_dirty)
 
 #ifdef CONFIG_SLUB_DEBUG
 #define SLABDEBUG (1 << PG_error)
@@ -138,6 +139,21 @@ static inline void ClearSlabDebug(struct
 	page->flags &= ~SLABDEBUG;
 }
 
+static inline int SlabKickable(struct page *page)
+{
+	return page->flags & KICKABLE;
+}
+
+static inline void SetSlabKickable(struct page *page)
+{
+	page->flags |= KICKABLE;
+}
+
+static inline void ClearSlabKickable(struct page *page)
+{
+	page->flags &= ~KICKABLE;
+}
+
 /*
  * Issues still to be resolved:
  *
@@ -1132,6 +1148,8 @@ static struct page *new_slab(struct kmem
 	if (s->flags & (SLAB_DEBUG_FREE | SLAB_RED_ZONE | SLAB_POISON |
 			SLAB_STORE_USER | SLAB_TRACE))
 		SetSlabDebug(page);
+	if (s->kick)
+		SetSlabKickable(page);
 
 	start = page_address(page);
 	page->end = start + 1;
@@ -1203,6 +1221,7 @@ static void discard_slab(struct kmem_cac
 
 	atomic_long_dec(&n->nr_slabs);
 	reset_page_mapcount(page);
+	ClearSlabKickable(page);
 	__ClearPageSlab(page);
 	free_slab(s, page);
 }
@@ -1383,6 +1402,8 @@ static void unfreeze_slab(struct kmem_ca
 			stat(c, DEACTIVATE_FULL);
 			if (SlabDebug(page) && (s->flags & SLAB_STORE_USER))
 				add_full(n, page);
+			if (s->kick)
+				SetSlabKickable(page);
 		}
 		slab_unlock(page);
 	} else {
@@ -2861,7 +2882,7 @@ static int kmem_cache_vacate(struct page
 	s = page->slab;
 	objects = s->objects;
 	map = scratch + max_defrag_slab_objects * sizeof(void **);
-	if (!page->inuse || !s->kick)
+	if (!page->inuse || !s->kick || !SlabKickable(page))
 		goto out;
 
 	/* Determine used objects */
@@ -2898,6 +2919,8 @@ out:
 	 * Check the result and unfreeze the slab
 	 */
 	leftover = page->inuse;
+	if (leftover)
+		ClearSlabKickable(page);
 	unfreeze_slab(s, page, leftover > 0);
 	local_irq_restore(flags);
 	return leftover;
@@ -2945,7 +2968,8 @@ static unsigned long __kmem_cache_shrink
 
 	spin_lock_irqsave(&n->list_lock, flags);
 	list_for_each_entry_safe(page, page2, &n->partial, lru) {
-		if (page->inuse > s->objects / 4)
+		if (page->inuse > s->objects / 4 ||
+				(s->kick && !SlabKickable(page)))
 			continue;
 		if (!slab_trylock(page))
 			continue;

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[patch 08/17] SLUB: Trigger defragmentation from memory reclaim

[Christoph Lameter]

[-- Attachment #1: 0053-SLUB-Trigger-defragmentation-from-memory-reclaim.patch --]
[-- Type: text/plain, Size: 5589 bytes --]

This patch triggers slab defragmentation from memory reclaim.
The logical point for this is after slab shrinking was performed in
vmscan.c. At that point the fragmentation ratio of a slab was increased
because objects were freed via the LRUs. So we call kmem_cache_defrag() from
there.

slab_shrink() from vmscan.c is called in some contexts to do
global shrinking of slabs and in others to do shrinking for
a particular zone. Pass the zone to slab_shrink, so that slab_shrink
can call kmem_cache_defrag() and restrict the defragmentation to
the node that is under memory pressure.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 fs/drop_caches.c   |    2 +-
 include/linux/mm.h |    2 +-
 mm/vmscan.c        |   26 +++++++++++++++++++-------
 3 files changed, 21 insertions(+), 9 deletions(-)

Index: linux-2.6/fs/drop_caches.c
===================================================================
--- linux-2.6.orig/fs/drop_caches.c	2008-02-14 15:19:11.833503223 -0800
+++ linux-2.6/fs/drop_caches.c	2008-02-15 15:47:14.688851790 -0800
@@ -50,7 +50,7 @@ void drop_slab(void)
 	int nr_objects;
 
 	do {
-		nr_objects = shrink_slab(1000, GFP_KERNEL, 1000);
+		nr_objects = shrink_slab(1000, GFP_KERNEL, 1000, NULL);
 	} while (nr_objects > 10);
 }
 
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c	2008-02-14 15:20:25.582017250 -0800
+++ linux-2.6/mm/vmscan.c	2008-02-15 15:47:14.724851829 -0800
@@ -173,10 +173,18 @@ EXPORT_SYMBOL(unregister_shrinker);
  * are eligible for the caller's allocation attempt.  It is used for balancing
  * slab reclaim versus page reclaim.
  *
+ * zone is the zone for which we are shrinking the slabs. If the intent
+ * is to do a global shrink then zone may be NULL. Specification of a
+ * zone is currently only used to limit slab defragmentation to a NUMA node.
+ * The performace of shrink_slab would be better (in particular under NUMA)
+ * if it could be targeted as a whole to the zone that is under memory
+ * pressure but the VFS infrastructure does not allow that at the present
+ * time.
+ *
  * Returns the number of slab objects which we shrunk.
  */
 unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
-			unsigned long lru_pages)
+			unsigned long lru_pages, struct zone *zone)
 {
 	struct shrinker *shrinker;
 	unsigned long ret = 0;
@@ -233,6 +241,8 @@ unsigned long shrink_slab(unsigned long 
 		shrinker->nr += total_scan;
 	}
 	up_read(&shrinker_rwsem);
+	if (gfp_mask & __GFP_FS)
+		kmem_cache_defrag(zone ? zone_to_nid(zone) : -1);
 	return ret;
 }
 
@@ -1352,7 +1362,7 @@ static unsigned long do_try_to_free_page
 		 * over limit cgroups
 		 */
 		if (scan_global_lru(sc)) {
-			shrink_slab(sc->nr_scanned, gfp_mask, lru_pages);
+			shrink_slab(sc->nr_scanned, gfp_mask, lru_pages, NULL);
 			if (reclaim_state) {
 				nr_reclaimed += reclaim_state->reclaimed_slab;
 				reclaim_state->reclaimed_slab = 0;
@@ -1581,7 +1591,7 @@ loop_again:
 				nr_reclaimed += shrink_zone(priority, zone, &sc);
 			reclaim_state->reclaimed_slab = 0;
 			nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
-						lru_pages);
+						lru_pages, zone);
 			nr_reclaimed += reclaim_state->reclaimed_slab;
 			total_scanned += sc.nr_scanned;
 			if (zone_is_all_unreclaimable(zone))
@@ -1822,7 +1832,7 @@ unsigned long shrink_all_memory(unsigned
 	/* If slab caches are huge, it's better to hit them first */
 	while (nr_slab >= lru_pages) {
 		reclaim_state.reclaimed_slab = 0;
-		shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
+		shrink_slab(nr_pages, sc.gfp_mask, lru_pages, NULL);
 		if (!reclaim_state.reclaimed_slab)
 			break;
 
@@ -1860,7 +1870,7 @@ unsigned long shrink_all_memory(unsigned
 
 			reclaim_state.reclaimed_slab = 0;
 			shrink_slab(sc.nr_scanned, sc.gfp_mask,
-					count_lru_pages());
+					count_lru_pages(), NULL);
 			ret += reclaim_state.reclaimed_slab;
 			if (ret >= nr_pages)
 				goto out;
@@ -1877,7 +1887,8 @@ unsigned long shrink_all_memory(unsigned
 	if (!ret) {
 		do {
 			reclaim_state.reclaimed_slab = 0;
-			shrink_slab(nr_pages, sc.gfp_mask, count_lru_pages());
+			shrink_slab(nr_pages, sc.gfp_mask,
+					count_lru_pages(), NULL);
 			ret += reclaim_state.reclaimed_slab;
 		} while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
 	}
@@ -2040,7 +2051,8 @@ static int __zone_reclaim(struct zone *z
 		 * Note that shrink_slab will free memory on all zones and may
 		 * take a long time.
 		 */
-		while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
+		while (shrink_slab(sc.nr_scanned, gfp_mask, order,
+						zone) &&
 			zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
 				slab_reclaimable - nr_pages)
 			;
Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h	2008-02-14 15:20:04.897873207 -0800
+++ linux-2.6/include/linux/mm.h	2008-02-15 15:47:14.736851869 -0800
@@ -1191,7 +1191,7 @@ int in_gate_area_no_task(unsigned long a
 int drop_caches_sysctl_handler(struct ctl_table *, int, struct file *,
 					void __user *, size_t *, loff_t *);
 unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
-			unsigned long lru_pages);
+			unsigned long lru_pages, struct zone *z);
 void drop_pagecache(void);
 void drop_slab(void);
 

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[patch 09/17] Buffer heads: Support slab defrag

[Christoph Lameter]

[-- Attachment #1: 0054-Buffer-heads-Support-slab-defrag.patch --]
[-- Type: text/plain, Size: 3491 bytes --]

Defragmentation support for buffer heads. We convert the references to
buffers to struct page references and try to remove the buffers from
those pages. If the pages are dirty then trigger writeout so that the
buffer heads can be removed later.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 fs/buffer.c |  101 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)

Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c	2008-02-14 15:19:11.157498510 -0800
+++ linux-2.6/fs/buffer.c	2008-02-15 15:49:05.537213877 -0800
@@ -3257,6 +3257,106 @@ int bh_submit_read(struct buffer_head *b
 }
 EXPORT_SYMBOL(bh_submit_read);
 
+/*
+ * Writeback a page to clean the dirty state
+ */
+static void trigger_write(struct page *page)
+{
+	struct address_space *mapping = page_mapping(page);
+	int rc;
+	struct writeback_control wbc = {
+		.sync_mode = WB_SYNC_NONE,
+		.nr_to_write = 1,
+		.range_start = 0,
+		.range_end = LLONG_MAX,
+		.nonblocking = 1,
+		.for_reclaim = 0
+	};
+
+	if (!mapping->a_ops->writepage)
+		/* No write method for the address space */
+		return;
+
+	if (!clear_page_dirty_for_io(page))
+		/* Someone else already triggered a write */
+		return;
+
+	rc = mapping->a_ops->writepage(page, &wbc);
+	if (rc < 0)
+		/* I/O Error writing */
+		return;
+
+	if (rc == AOP_WRITEPAGE_ACTIVATE)
+		unlock_page(page);
+}
+
+/*
+ * Get references on buffers.
+ *
+ * We obtain references on the page that uses the buffer. v[i] will point to
+ * the corresponding page after get_buffers() is through.
+ *
+ * We are safe from the underlying page being removed simply by doing
+ * a get_page_unless_zero. The buffer head removal may race at will.
+ * try_to_free_buffes will later take appropriate locks to remove the
+ * buffers if they are still there.
+ */
+static void *get_buffers(struct kmem_cache *s, int nr, void **v)
+{
+	struct page *page;
+	struct buffer_head *bh;
+	int i,j;
+	int n = 0;
+
+	for (i = 0; i < nr; i++) {
+		bh = v[i];
+		v[i] = NULL;
+
+		page = bh->b_page;
+
+		if (page && PagePrivate(page)) {
+			for (j = 0; j < n; j++)
+				if (page == v[j])
+					goto cont;
+		}
+
+		if (get_page_unless_zero(page))
+			v[n++] = page;
+cont:	;
+	}
+	return NULL;
+}
+
+/*
+ * Despite its name: kick_buffers operates on a list of pointers to
+ * page structs that was setup by get_buffer
+ */
+static void kick_buffers(struct kmem_cache *s, int nr, void **v,
+							void *private)
+{
+	struct page *page;
+	int i;
+
+	for (i = 0; i < nr; i++) {
+		page = v[i];
+
+		if (!page || PageWriteback(page))
+			continue;
+
+
+		if (!TestSetPageLocked(page)) {
+			if (PageDirty(page))
+				trigger_write(page);
+			else {
+				if (PagePrivate(page))
+					try_to_free_buffers(page);
+				unlock_page(page);
+			}
+		}
+		put_page(page);
+	}
+}
+
 static void
 init_buffer_head(struct kmem_cache *cachep, void *data)
 {
@@ -3275,6 +3375,7 @@ void __init buffer_init(void)
 				(SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
 				SLAB_MEM_SPREAD),
 				init_buffer_head);
+	kmem_cache_setup_defrag(bh_cachep, get_buffers, kick_buffers);
 
 	/*
 	 * Limit the bh occupancy to 10% of ZONE_NORMAL

-- 

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[patch 10/17] inodes: Support generic defragmentation

[Christoph Lameter]

[-- Attachment #1: 0055-inodes-Support-generic-defragmentation.patch --]
[-- Type: text/plain, Size: 4295 bytes --]

This implements the ability to remove inodes in a particular slab
from inode caches. In order to remove an inode we may have to write out
the pages of an inode, the inode itself and remove the dentries referring
to the node.

Provide generic functionality that can be used by filesystems that have
their own inode caches to also tie into the defragmentation functions
that are made available here.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 fs/inode.c         |   96 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |    6 +++
 2 files changed, 102 insertions(+)

Index: linux-2.6/fs/inode.c
===================================================================
--- linux-2.6.orig/fs/inode.c	2008-02-14 15:19:12.457507589 -0800
+++ linux-2.6/fs/inode.c	2008-02-15 15:49:22.309268623 -0800
@@ -1370,6 +1370,101 @@ static int __init set_ihash_entries(char
 }
 __setup("ihash_entries=", set_ihash_entries);
 
+void *get_inodes(struct kmem_cache *s, int nr, void **v)
+{
+	int i;
+
+	spin_lock(&inode_lock);
+	for (i = 0; i < nr; i++) {
+		struct inode *inode = v[i];
+
+		if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE))
+			v[i] = NULL;
+		else
+			__iget(inode);
+	}
+	spin_unlock(&inode_lock);
+	return NULL;
+}
+EXPORT_SYMBOL(get_inodes);
+
+/*
+ * Function for filesystems that embedd struct inode into their own
+ * structures. The offset is the offset of the struct inode in the fs inode.
+ */
+void *fs_get_inodes(struct kmem_cache *s, int nr, void **v,
+						unsigned long offset)
+{
+	int i;
+
+	for (i = 0; i < nr; i++)
+		v[i] += offset;
+
+	return get_inodes(s, nr, v);
+}
+EXPORT_SYMBOL(fs_get_inodes);
+
+void kick_inodes(struct kmem_cache *s, int nr, void **v, void *private)
+{
+	struct inode *inode;
+	int i;
+	int abort = 0;
+	LIST_HEAD(freeable);
+	struct super_block *sb;
+
+	for (i = 0; i < nr; i++) {
+		inode = v[i];
+		if (!inode)
+			continue;
+
+		if (inode_has_buffers(inode) || inode->i_data.nrpages) {
+			if (remove_inode_buffers(inode))
+				invalidate_mapping_pages(&inode->i_data,
+								0, -1);
+		}
+
+		/* Invalidate children and dentry */
+		if (S_ISDIR(inode->i_mode)) {
+			struct dentry *d = d_find_alias(inode);
+
+			if (d) {
+				d_invalidate(d);
+				dput(d);
+			}
+		}
+
+		if (inode->i_state & I_DIRTY)
+			write_inode_now(inode, 1);
+
+		d_prune_aliases(inode);
+	}
+
+	mutex_lock(&iprune_mutex);
+	for (i = 0; i < nr; i++) {
+		inode = v[i];
+		if (!inode)
+			continue;
+
+		sb = inode->i_sb;
+		iput(inode);
+		if (abort || !(sb->s_flags & MS_ACTIVE))
+			continue;
+
+		spin_lock(&inode_lock);
+		abort =  !can_unuse(inode);
+
+		if (!abort) {
+			list_move(&inode->i_list, &freeable);
+			inode->i_state |= I_FREEING;
+			inodes_stat.nr_unused--;
+		}
+		spin_unlock(&inode_lock);
+	}
+	dispose_list(&freeable);
+	mutex_unlock(&iprune_mutex);
+}
+EXPORT_SYMBOL(kick_inodes);
+
 /*
  * Initialize the waitqueues and inode hash table.
  */
@@ -1409,6 +1504,7 @@ void __init inode_init(void)
 					 SLAB_MEM_SPREAD),
 					 init_once);
 	register_shrinker(&icache_shrinker);
+	kmem_cache_setup_defrag(inode_cachep, get_inodes, kick_inodes);
 
 	/* Hash may have been set up in inode_init_early */
 	if (!hashdist)
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h	2008-02-15 10:48:35.463846699 -0800
+++ linux-2.6/include/linux/fs.h	2008-02-15 15:49:22.309268623 -0800
@@ -1787,6 +1787,12 @@ static inline void insert_inode_hash(str
 	__insert_inode_hash(inode, inode->i_ino);
 }
 
+/* Helper functions for inode defragmentation support in filesystems */
+extern void kick_inodes(struct kmem_cache *, int, void **, void *);
+extern void *get_inodes(struct kmem_cache *, int nr, void **);
+extern void *fs_get_inodes(struct kmem_cache *, int nr, void **,
+						unsigned long offset);
+
 extern struct file * get_empty_filp(void);
 extern void file_move(struct file *f, struct list_head *list);
 extern void file_kill(struct file *f);

-- 

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[patch 11/17] FS: ExtX filesystem defrag

[Christoph Lameter]

[-- Attachment #1: 0056-FS-ExtX-filesystem-defrag.patch --]
[-- Type: text/plain, Size: 3086 bytes --]

Support defragmentation for extX filesystem inodes

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 fs/ext2/super.c |    9 +++++++++
 fs/ext3/super.c |    8 ++++++++
 fs/ext4/super.c |    8 ++++++++
 3 files changed, 25 insertions(+)

Index: linux-2.6.24-rc6-mm1/fs/ext2/super.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/fs/ext2/super.c	2007-12-26 17:47:01.987405542 -0800
+++ linux-2.6.24-rc6-mm1/fs/ext2/super.c	2007-12-27 12:04:37.798315149 -0800
@@ -171,6 +171,12 @@ static void init_once(struct kmem_cache 
 	inode_init_once(&ei->vfs_inode);
 }
 
+static void *ext2_get_inodes(struct kmem_cache *s, int nr, void **v)
+{
+	return fs_get_inodes(s, nr, v,
+		offsetof(struct ext2_inode_info, vfs_inode));
+}
+
 static int init_inodecache(void)
 {
 	ext2_inode_cachep = kmem_cache_create("ext2_inode_cache",
@@ -180,6 +186,9 @@ static int init_inodecache(void)
 					     init_once);
 	if (ext2_inode_cachep == NULL)
 		return -ENOMEM;
+
+	kmem_cache_setup_defrag(ext2_inode_cachep,
+			ext2_get_inodes, kick_inodes);
 	return 0;
 }
 
Index: linux-2.6.24-rc6-mm1/fs/ext3/super.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/fs/ext3/super.c	2007-12-26 17:47:01.995405564 -0800
+++ linux-2.6.24-rc6-mm1/fs/ext3/super.c	2007-12-27 12:04:37.802315408 -0800
@@ -484,6 +484,12 @@ static void init_once(struct kmem_cache 
 	inode_init_once(&ei->vfs_inode);
 }
 
+static void *ext3_get_inodes(struct kmem_cache *s, int nr, void **v)
+{
+	return fs_get_inodes(s, nr, v,
+		offsetof(struct ext3_inode_info, vfs_inode));
+}
+
 static int init_inodecache(void)
 {
 	ext3_inode_cachep = kmem_cache_create("ext3_inode_cache",
@@ -493,6 +499,8 @@ static int init_inodecache(void)
 					     init_once);
 	if (ext3_inode_cachep == NULL)
 		return -ENOMEM;
+	kmem_cache_setup_defrag(ext3_inode_cachep,
+			ext3_get_inodes, kick_inodes);
 	return 0;
 }
 
Index: linux-2.6.24-rc6-mm1/fs/ext4/super.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/fs/ext4/super.c	2007-12-26 17:47:02.011405842 -0800
+++ linux-2.6.24-rc6-mm1/fs/ext4/super.c	2007-12-27 12:04:37.814315317 -0800
@@ -600,6 +600,12 @@ static void init_once(struct kmem_cache 
 	inode_init_once(&ei->vfs_inode);
 }
 
+static void *ext4_get_inodes(struct kmem_cache *s, int nr, void **v)
+{
+	return fs_get_inodes(s, nr, v,
+		offsetof(struct ext4_inode_info, vfs_inode));
+}
+
 static int init_inodecache(void)
 {
 	ext4_inode_cachep = kmem_cache_create("ext4_inode_cache",
@@ -609,6 +615,8 @@ static int init_inodecache(void)
 					     init_once);
 	if (ext4_inode_cachep == NULL)
 		return -ENOMEM;
+	kmem_cache_setup_defrag(ext4_inode_cachep,
+			ext4_get_inodes, kick_inodes);
 	return 0;
 }
 

-- 

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[patch 12/17] FS: XFS slab defragmentation

[Christoph Lameter]

[-- Attachment #1: 0057-FS-XFS-slab-defragmentation.patch --]
[-- Type: text/plain, Size: 1046 bytes --]

Support inode defragmentation for xfs

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 fs/xfs/linux-2.6/xfs_super.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux-2.6/fs/xfs/linux-2.6/xfs_super.c
===================================================================
--- linux-2.6.orig/fs/xfs/linux-2.6/xfs_super.c	2008-02-14 15:19:13.781516819 -0800
+++ linux-2.6/fs/xfs/linux-2.6/xfs_super.c	2008-02-15 15:49:28.377288588 -0800
@@ -862,6 +862,7 @@ xfs_init_zones(void)
 	xfs_ioend_zone = kmem_zone_init(sizeof(xfs_ioend_t), "xfs_ioend");
 	if (!xfs_ioend_zone)
 		goto out_destroy_vnode_zone;
+	kmem_cache_setup_defrag(xfs_vnode_zone, get_inodes, kick_inodes);
 
 	xfs_ioend_pool = mempool_create_slab_pool(4 * MAX_BUF_PER_PAGE,
 						  xfs_ioend_zone);

-- 

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[patch 13/17] FS: Proc filesystem support for slab defrag

[Christoph Lameter]

[-- Attachment #1: 0058-FS-Proc-filesystem-support-for-slab-defrag.patch --]
[-- Type: text/plain, Size: 1319 bytes --]

Support procfs inode defragmentation

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 fs/proc/inode.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: linux-2.6.24-rc6-mm1/fs/proc/inode.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/fs/proc/inode.c	2007-12-26 17:47:03.223412165 -0800
+++ linux-2.6.24-rc6-mm1/fs/proc/inode.c	2007-12-27 12:04:43.742341773 -0800
@@ -104,6 +104,12 @@ static void init_once(struct kmem_cache 
 	inode_init_once(&ei->vfs_inode);
 }
 
+static void *proc_get_inodes(struct kmem_cache *s, int nr, void **v)
+{
+	return fs_get_inodes(s, nr, v,
+		offsetof(struct proc_inode, vfs_inode));
+};
+
 int __init proc_init_inodecache(void)
 {
 	proc_inode_cachep = kmem_cache_create("proc_inode_cache",
@@ -111,6 +117,8 @@ int __init proc_init_inodecache(void)
 					     0, (SLAB_RECLAIM_ACCOUNT|
 						SLAB_MEM_SPREAD|SLAB_PANIC),
 					     init_once);
+	kmem_cache_setup_defrag(proc_inode_cachep,
+				proc_get_inodes, kick_inodes);
 	return 0;
 }
 

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[patch 14/17] FS: Slab defrag: Reiserfs support

[Christoph Lameter]

[-- Attachment #1: 0059-FS-Slab-defrag-Reiserfs-support.patch --]
[-- Type: text/plain, Size: 1328 bytes --]

Slab defragmentation: Support reiserfs inode defragmentation

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 fs/reiserfs/super.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: linux-2.6.24-rc6-mm1/fs/reiserfs/super.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/fs/reiserfs/super.c	2007-12-26 17:47:05.407423958 -0800
+++ linux-2.6.24-rc6-mm1/fs/reiserfs/super.c	2007-12-27 12:04:46.718354502 -0800
@@ -532,6 +532,12 @@ static void init_once(struct kmem_cache 
 #endif
 }
 
+static void *reiserfs_get_inodes(struct kmem_cache *s, int nr, void **v)
+{
+	return fs_get_inodes(s, nr, v,
+		offsetof(struct reiserfs_inode_info, vfs_inode));
+}
+
 static int init_inodecache(void)
 {
 	reiserfs_inode_cachep = kmem_cache_create("reiser_inode_cache",
@@ -542,6 +548,8 @@ static int init_inodecache(void)
 						  init_once);
 	if (reiserfs_inode_cachep == NULL)
 		return -ENOMEM;
+	kmem_cache_setup_defrag(reiserfs_inode_cachep,
+			reiserfs_get_inodes, kick_inodes);
 	return 0;
 }
 

-- 

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[patch 15/17] FS: Socket inode defragmentation

[Christoph Lameter]

[-- Attachment #1: 0060-FS-Socket-inode-defragmentation.patch --]
[-- Type: text/plain, Size: 1228 bytes --]

Support inode defragmentation for sockets

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 net/socket.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: mm/net/socket.c
===================================================================
--- mm.orig/net/socket.c	2007-11-28 12:28:01.311962427 -0800
+++ mm/net/socket.c	2007-11-28 12:31:46.383962876 -0800
@@ -269,6 +269,12 @@ static void init_once(struct kmem_cache 
 	inode_init_once(&ei->vfs_inode);
 }
 
+static void *sock_get_inodes(struct kmem_cache *s, int nr, void **v)
+{
+	return fs_get_inodes(s, nr, v,
+		offsetof(struct socket_alloc, vfs_inode));
+}
+
 static int init_inodecache(void)
 {
 	sock_inode_cachep = kmem_cache_create("sock_inode_cache",
@@ -280,6 +286,8 @@ static int init_inodecache(void)
 					      init_once);
 	if (sock_inode_cachep == NULL)
 		return -ENOMEM;
+	kmem_cache_setup_defrag(sock_inode_cachep,
+			sock_get_inodes, kick_inodes);
 	return 0;
 }
 

-- 

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[patch 16/17] dentries: Add constructor

[Christoph Lameter]

[-- Attachment #1: 0061-dentries-Add-constructor.patch --]
[-- Type: text/plain, Size: 2412 bytes --]

In order to support defragmentation on the dentry cache we need to have
a determined object state at all times. Without a constructor the object
would have a random state after allocation.

So provide a constructor.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 fs/dcache.c |   26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c	2008-02-15 10:48:35.011844303 -0800
+++ linux-2.6/fs/dcache.c	2008-02-15 15:49:39.169323892 -0800
@@ -870,6 +870,16 @@ static struct shrinker dcache_shrinker =
 	.seeks = DEFAULT_SEEKS,
 };
 
+void dcache_ctor(struct kmem_cache *s, void *p)
+{
+	struct dentry *dentry = p;
+
+	spin_lock_init(&dentry->d_lock);
+	dentry->d_inode = NULL;
+	INIT_LIST_HEAD(&dentry->d_lru);
+	INIT_LIST_HEAD(&dentry->d_alias);
+}
+
 /**
  * d_alloc	-	allocate a dcache entry
  * @parent: parent of entry to allocate
@@ -907,8 +917,6 @@ struct dentry *d_alloc(struct dentry * p
 
 	atomic_set(&dentry->d_count, 1);
 	dentry->d_flags = DCACHE_UNHASHED;
-	spin_lock_init(&dentry->d_lock);
-	dentry->d_inode = NULL;
 	dentry->d_parent = NULL;
 	dentry->d_sb = NULL;
 	dentry->d_op = NULL;
@@ -918,9 +926,7 @@ struct dentry *d_alloc(struct dentry * p
 	dentry->d_cookie = NULL;
 #endif
 	INIT_HLIST_NODE(&dentry->d_hash);
-	INIT_LIST_HEAD(&dentry->d_lru);
 	INIT_LIST_HEAD(&dentry->d_subdirs);
-	INIT_LIST_HEAD(&dentry->d_alias);
 
 	if (parent) {
 		dentry->d_parent = dget(parent);
@@ -2098,14 +2104,10 @@ static void __init dcache_init(void)
 {
 	int loop;
 
-	/* 
-	 * A constructor could be added for stable state like the lists,
-	 * but it is probably not worth it because of the cache nature
-	 * of the dcache. 
-	 */
-	dentry_cache = KMEM_CACHE(dentry,
-		SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
-	
+	dentry_cache = kmem_cache_create("dentry_cache", sizeof(struct dentry),
+		0, SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD,
+		dcache_ctor);
+
 	register_shrinker(&dcache_shrinker);
 
 	/* Hash may have been set up in dcache_init_early */

-- 

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[patch 17/17] dentries: dentry defragmentation

[Christoph Lameter]

[-- Attachment #1: 0062-dentries-dentry-defragmentation.patch --]
[-- Type: text/plain, Size: 4291 bytes --]

The dentry pruning for unused entries works in a straightforward way. It
could be made more aggressive if one would actually move dentries instead
of just reclaiming them.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 fs/dcache.c |  101 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 100 insertions(+), 1 deletion(-)

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c	2008-02-15 15:49:39.169323892 -0800
+++ linux-2.6/fs/dcache.c	2008-02-15 15:49:46.301347228 -0800
@@ -31,6 +31,7 @@
 #include <linux/seqlock.h>
 #include <linux/swap.h>
 #include <linux/bootmem.h>
+#include <linux/backing-dev.h>
 #include "internal.h"
 
 
@@ -143,7 +144,10 @@ static struct dentry *d_kill(struct dent
 
 	list_del(&dentry->d_u.d_child);
 	dentry_stat.nr_dentry--;	/* For d_free, below */
-	/*drops the locks, at that point nobody can reach this dentry */
+	/*
+	 * drops the locks, at that point nobody (aside from defrag)
+	 * can reach this dentry
+	 */
 	dentry_iput(dentry);
 	parent = dentry->d_parent;
 	d_free(dentry);
@@ -2100,6 +2104,100 @@ static void __init dcache_init_early(voi
 		INIT_HLIST_HEAD(&dentry_hashtable[loop]);
 }
 
+/*
+ * The slab allocator is holding off frees. We can safely examine
+ * the object without the danger of it vanishing from under us.
+ */
+static void *get_dentries(struct kmem_cache *s, int nr, void **v)
+{
+	struct dentry *dentry;
+	int i;
+
+	spin_lock(&dcache_lock);
+	for (i = 0; i < nr; i++) {
+		dentry = v[i];
+
+		/*
+		 * Three sorts of dentries cannot be reclaimed:
+		 *
+		 * 1. dentries that are in the process of being allocated
+		 *    or being freed. In that case the dentry is neither
+		 *    on the LRU nor hashed.
+		 *
+		 * 2. Fake hashed entries as used for anonymous dentries
+		 *    and pipe I/O. The fake hashed entries have d_flags
+		 *    set to indicate a hashed entry. However, the
+		 *    d_hash field indicates that the entry is not hashed.
+		 *
+		 * 3. dentries that have a backing store that is not
+		 *    writable. This is true for tmpsfs and other in
+		 *    memory filesystems. Removing dentries from them
+		 *    would loose dentries for good.
+		 */
+		if ((d_unhashed(dentry) && list_empty(&dentry->d_lru)) ||
+		   (!d_unhashed(dentry) && hlist_unhashed(&dentry->d_hash)) ||
+		   (dentry->d_inode &&
+		   !mapping_cap_writeback_dirty(dentry->d_inode->i_mapping)))
+			/* Ignore this dentry */
+			v[i] = NULL;
+		else
+			/* dget_locked will remove the dentry from the LRU */
+			dget_locked(dentry);
+	}
+	spin_unlock(&dcache_lock);
+	return NULL;
+}
+
+/*
+ * Slab has dropped all the locks. Get rid of the refcount obtained
+ * earlier and also free the object.
+ */
+static void kick_dentries(struct kmem_cache *s,
+				int nr, void **v, void *private)
+{
+	struct dentry *dentry;
+	int i;
+
+	/*
+	 * First invalidate the dentries without holding the dcache lock
+	 */
+	for (i = 0; i < nr; i++) {
+		dentry = v[i];
+
+		if (dentry)
+			d_invalidate(dentry);
+	}
+
+	/*
+	 * If we are the last one holding a reference then the dentries can
+	 * be freed. We need the dcache_lock.
+	 */
+	spin_lock(&dcache_lock);
+	for (i = 0; i < nr; i++) {
+		dentry = v[i];
+		if (!dentry)
+			continue;
+
+		spin_lock(&dentry->d_lock);
+		if (atomic_read(&dentry->d_count) > 1) {
+			spin_unlock(&dentry->d_lock);
+			spin_unlock(&dcache_lock);
+			dput(dentry);
+			spin_lock(&dcache_lock);
+			continue;
+		}
+
+		prune_one_dentry(dentry);
+	}
+	spin_unlock(&dcache_lock);
+
+	/*
+	 * dentries are freed using RCU so we need to wait until RCU
+	 * operations are complete
+	 */
+	synchronize_rcu();
+}
+
 static void __init dcache_init(void)
 {
 	int loop;
@@ -2109,6 +2207,7 @@ static void __init dcache_init(void)
 		dcache_ctor);
 
 	register_shrinker(&dcache_shrinker);
+	kmem_cache_setup_defrag(dentry_cache, get_dentries, kick_dentries);
 
 	/* Hash may have been set up in dcache_init_early */
 	if (!hashdist)

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Re: [patch 00/17] Slab Fragmentation Reduction V10

[Andrew Morton]

On Fri, 15 Feb 2008 16:45:26 -0800 Christoph Lameter <clameter@sgi.com> wrote:

> Slab fragmentation is mainly an issue if Linux is used as a fileserver
> and large amounts of dentries, inodes and buffer heads accumulate. In some
> load situations the slabs become very sparsely populated so that a lot of
> memory is wasted by slabs that only contain one or a few objects. In
> extreme cases the performance of a machine will become sluggish since
> we are continually running reclaim. Slab defragmentation adds the
> capability to recover the memory that is wasted.

I'm somewhat reluctant to consider this because it is slub-only, and slub
doesn't appear to be doing so well on the performance front wrt slab.

We do need to make one of those implementations go away, and if it's slub
that goes, we have a lump of defrag code hanging around in core VFS which
isn't used by anything.

So I think the first thing we need to do is to establish that slub is
viable as our only slab allocator (ignoring slob here).  And if that means
tweaking the heck out of slub until it's competitive, we would be
duty-bound to ask "how fast will slab be if we do that much tweaking to
it as well".

Another basis for comparison is "which one uses the lowest-order
allocations to achieve its performance".

Of course, current performance isn't the only thing - it could be that slub
enables features such as defrag which wouldn't be possible with slab.  We
can discuss that.

But one of these implementations needs to go away, and that decision
shouldn't be driven by the fact that we happen to have already implemented
some additional features on top of one of them.

hm?

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Re: [patch 00/17] Slab Fragmentation Reduction V10

[Andi Kleen]

I personally would really like to see d/icache fragmentation in
one form or another. It's a serious long standing Linux issue
that would be really good to solve finally.

> So I think the first thing we need to do is to establish that slub is
> viable as our only slab allocator (ignoring slob here).  And if that means
> tweaking the heck out of slub until it's competitive, we would be
> duty-bound to ask "how fast will slab be if we do that much tweaking to
> it as well".

There's another aspect: slab is quite unreadable and very hairy code.
slub is much cleaner. On the maintainability front slub wins easily. 

> Another basis for comparison is "which one uses the lowest-order
> allocations to achieve its performance".

That's an important point I agree. It directly translates into
reliability under load and that is very important.

> But one of these implementations needs to go away, and that decision

I don't think slab is a good candidate to keep because it's so hard 
to hack on. Especially since the slab NUMA changes the code flow and
data structures are really really hairy and I doubt there are many people 
left who understand it. e.g. I tracked down an RT bug in slab some
time ago and it was a really unpleasant experience.

In the end even if it is slightly slower today the code
that is easiest to improve will be faster/better longer term.

I'm a little sceptical about the high order allocations in slub too 
though. Christoph seems to think they're not a big deal, but that is 
against a lot of conventional Linux wisdom at least.

That is one area that probably needs to be explored more.

-Andi

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Re: [patch 00/17] Slab Fragmentation Reduction V10

[Christoph Lameter]

On Sat, 23 Feb 2008, Andi Kleen wrote:

> I'm a little sceptical about the high order allocations in slub too 
> though. Christoph seems to think they're not a big deal, but that is 
> against a lot of conventional Linux wisdom at least.
> 
> That is one area that probably needs to be explored more.

Well there is a patchset that I posted recently that allows any slub alloc 
to fallback to an order 0 alloc. That is something slab cannot do.

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