Re: [PATCH] SLUB use cmpxchg_local

[Christoph Lameter]

Here is the current cmpxchg_local version that I used for testing.

Signed-off-by: Christoph Lameter <clameter@xxxxxxx>

---
 include/linux/slub_def.h |   10 +++---
 mm/slub.c                |   74 ++++++++++++++++++++++++++++++++---------------
 2 files changed, 56 insertions(+), 28 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2007-08-21 22:34:30.000000000 -0700
+++ linux-2.6/mm/slub.c	2007-08-22 02:07:26.000000000 -0700
@@ -1442,13 +1442,18 @@ static void *__slab_alloc(struct kmem_ca
 {
 	void **object;
 	struct page *new;
+	unsigned long flags;
 
+	local_irq_save(flags);
+	put_cpu_no_resched();
 	if (!c->page)
+		/* Slab was flushed */
 		goto new_slab;
 
 	slab_lock(c->page);
 	if (unlikely(!node_match(c, node)))
 		goto another_slab;
+
 load_freelist:
 	object = c->page->freelist;
 	if (unlikely(!object))
@@ -1457,11 +1462,15 @@ load_freelist:
 		goto debug;
 
 	object = c->page->freelist;
-	c->freelist = object[c->offset];
 	c->page->inuse = s->objects;
 	c->page->freelist = NULL;
 	c->node = page_to_nid(c->page);
+	c->freelist = object[c->offset];
+out:
 	slab_unlock(c->page);
+	local_irq_restore(flags);
+	if (unlikely((gfpflags & __GFP_ZERO)))
+		memset(object, 0, c->objsize);
 	return object;
 
 another_slab:
@@ -1502,6 +1511,7 @@ new_slab:
 		c->page = new;
 		goto load_freelist;
 	}
+	local_irq_restore(flags);
 	return NULL;
 debug:
 	object = c->page->freelist;
@@ -1511,8 +1521,7 @@ debug:
 	c->page->inuse++;
 	c->page->freelist = object[c->offset];
 	c->node = -1;
-	slab_unlock(c->page);
-	return object;
+	goto out;
 }
 
 /*
@@ -1529,25 +1538,29 @@ static void __always_inline *slab_alloc(
 		gfp_t gfpflags, int node, void *addr)
 {
 	void **object;
-	unsigned long flags;
 	struct kmem_cache_cpu *c;
 
-	local_irq_save(flags);
-	c = get_cpu_slab(s, smp_processor_id());
-	if (unlikely(!c->freelist || !node_match(c, node)))
+	c = get_cpu_slab(s, get_cpu());
+redo:
+	object = c->freelist;
+	if (unlikely(!object))
+		goto slow;
 
-		object = __slab_alloc(s, gfpflags, node, addr, c);
+	if (unlikely(!node_match(c, node)))
+		goto slow;
 
-	else {
-		object = c->freelist;
-		c->freelist = object[c->offset];
-	}
-	local_irq_restore(flags);
+	if (unlikely(cmpxchg_local(&c->freelist, object,
+		object[c->offset]) != object))
+			goto redo;
 
-	if (unlikely((gfpflags & __GFP_ZERO) && object))
+	put_cpu();
+	if (unlikely((gfpflags & __GFP_ZERO)))
 		memset(object, 0, c->objsize);
 
 	return object;
+slow:
+	return __slab_alloc(s, gfpflags, node, addr, c);
+
 }
 
 void *kmem_cache_alloc(struct kmem_cache *s, gfp_t gfpflags)
@@ -1577,7 +1590,10 @@ static void __slab_free(struct kmem_cach
 {
 	void *prior;
 	void **object = (void *)x;
+	unsigned long flags;
 
+	local_irq_save(flags);
+	put_cpu_no_resched();
 	slab_lock(page);
 
 	if (unlikely(SlabDebug(page)))
@@ -1603,6 +1619,7 @@ checks_ok:
 
 out_unlock:
 	slab_unlock(page);
+	local_irq_restore(flags);
 	return;
 
 slab_empty:
@@ -1613,6 +1630,7 @@ slab_empty:
 		remove_partial(s, page);
 
 	slab_unlock(page);
+	local_irq_restore(flags);
 	discard_slab(s, page);
 	return;
 
@@ -1637,19 +1655,29 @@ static void __always_inline slab_free(st
 			struct page *page, void *x, void *addr)
 {
 	void **object = (void *)x;
-	unsigned long flags;
+	void **freelist;
 	struct kmem_cache_cpu *c;
 
-	local_irq_save(flags);
 	debug_check_no_locks_freed(object, s->objsize);
-	c = get_cpu_slab(s, smp_processor_id());
-	if (likely(page == c->page && c->node >= 0)) {
-		object[c->offset] = c->freelist;
-		c->freelist = object;
-	} else
-		__slab_free(s, page, x, addr, c->offset);
 
-	local_irq_restore(flags);
+	c = get_cpu_slab(s, get_cpu());
+	if (unlikely(c->node < 0))
+		goto slow;
+redo:
+	freelist = c->freelist;
+	barrier();	/* If interrupt changes c->page -> cmpxchg failure */
+	if (unlikely(page != c->page))
+		goto slow;
+
+	object[c->offset] = freelist;
+	if (unlikely(cmpxchg_local(&c->freelist, freelist, object)
+							!= freelist))
+		goto redo;
+
+	put_cpu();
+	return;
+slow:
+	__slab_free(s, page, x, addr, c->offset);
 }
 
 void kmem_cache_free(struct kmem_cache *s, void *x)
Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h	2007-08-21 22:34:30.000000000 -0700
+++ linux-2.6/include/linux/slub_def.h	2007-08-22 01:56:05.000000000 -0700
@@ -12,11 +12,11 @@
 #include <linux/kobject.h>
 
 struct kmem_cache_cpu {
-	void **freelist;
-	struct page *page;
-	int node;
-	unsigned int offset;
-	unsigned int objsize;
+	void **freelist;	/* Updated through local atomic ops */
+	struct page *page;	/* Updated with interrupts disabled */
+	int node;		/* Updated with interrupts disabled */
+	unsigned int offset;	/* Set up on kmem_cache_create() */
+	unsigned int objsize;	/* Set up on kmem_cache_create() */
 };
 
 struct kmem_cache_node {

-
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