linux-kernel - Re: [patch 2/2]slub: add a type for slab partial list position

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Date:	Wed, 24 Aug 2011 08:57:52 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"penberg@...nel.org" <penberg@...nel.org>,
	"Shi, Alex" <alex.shi@...el.com>,
	"Chen, Tim C" <tim.c.chen@...el.com>
Subject: Re: [patch 2/2]slub: add a type for slab partial list position

On Tue, 2011-08-23 at 23:25 +0800, Christoph Lameter wrote:
> On Tue, 23 Aug 2011, Shaohua Li wrote:
> 
> > Adding slab to partial list head/tail is sensentive to performance.
> > So adding a type to document it to avoid we get it wrong.
> 
> I think that if you want to make it more descriptive then using the stats
> values (DEACTIVATE_TO_TAIL/HEAD) would avoid having to introduce an
> additional enum and it would also avoid the if statement in the stat call.
ok, that's better.

Subject: slub: explicitly document position of inserting slab to partial list

Adding slab to partial list head/tail is sensitive to performance.
So explicitly uses DEACTIVATE_TO_TAIL/DEACTIVATE_TO_HEAD to document
it to avoid we get it wrong.

Signed-off-by: Shaohua Li <shli@...nel.org>
Signed-off-by: Shaohua Li <shaohua.li@...el.com>
---
 mm/slub.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c	2011-08-24 08:46:27.000000000 +0800
+++ linux/mm/slub.c	2011-08-24 08:49:41.000000000 +0800
@@ -1534,7 +1534,7 @@ static inline void add_partial(struct km
 				struct page *page, int tail)
 {
 	n->nr_partial++;
-	if (tail)
+	if (tail == DEACTIVATE_TO_TAIL)
 		list_add_tail(&page->lru, &n->partial);
 	else
 		list_add(&page->lru, &n->partial);
@@ -1781,13 +1781,13 @@ static void deactivate_slab(struct kmem_
 	enum slab_modes l = M_NONE, m = M_NONE;
 	void *freelist;
 	void *nextfree;
-	int tail = 0;
+	int tail = DEACTIVATE_TO_HEAD;
 	struct page new;
 	struct page old;
 
 	if (page->freelist) {
 		stat(s, DEACTIVATE_REMOTE_FREES);
-		tail = 1;
+		tail = DEACTIVATE_TO_TAIL;
 	}
 
 	c->tid = next_tid(c->tid);
@@ -1893,7 +1893,7 @@ redo:
 		if (m == M_PARTIAL) {
 
 			add_partial(n, page, tail);
-			stat(s, tail ? DEACTIVATE_TO_TAIL : DEACTIVATE_TO_HEAD);
+			stat(s, tail);
 
 		} else if (m == M_FULL) {
 
@@ -2377,7 +2377,7 @@ static void __slab_free(struct kmem_cach
 		 */
 		if (unlikely(!prior)) {
 			remove_full(s, page);
-			add_partial(n, page, 1);
+			add_partial(n, page, DEACTIVATE_TO_TAIL);
 			stat(s, FREE_ADD_PARTIAL);
 		}
 	}
@@ -2695,7 +2695,7 @@ static void early_kmem_cache_node_alloc(
 	init_kmem_cache_node(n, kmem_cache_node);
 	inc_slabs_node(kmem_cache_node, node, page->objects);
 
-	add_partial(n, page, 0);
+	add_partial(n, page, DEACTIVATE_TO_HEAD);
 }
 
 static void free_kmem_cache_nodes(struct kmem_cache *s)


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