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

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Date:	Mon, 29 Aug 2011 11:06:27 +0800
From:	"Alex,Shi" <alex.shi@...el.com>
To:	"Li, Shaohua" <shaohua.li@...el.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"penberg@...nel.org" <penberg@...nel.org>,
	"Chen, Tim C" <tim.c.chen@...el.com>
Subject: Re: [patch 2/2]slub: add a type for slab partial list position

On Wed, 2011-08-24 at 08:57 +0800, Li, Shaohua wrote:
> 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.

Frankly speaking, using DEACTIVATE_TO_TAIL/DEACTIVATE_TO_HEAD in
slab_alloc, slab_free make code hard to understand. Just adding some
comments will be more clear and understandable. like the following: 
Do you think so? 


--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2377,6 +2377,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
                 */
                if (unlikely(!prior)) {
                        remove_full(s, page);
+                       /* only one object left in the page, so add to partial tail */
                        add_partial(n, page, 1);
                        stat(s, FREE_ADD_PARTIAL);
                }


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