linux-kernel - Re: [PATCH] fs: buffer_head, remove kmem_cache constructor to reduce memory usage under slub

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Message-ID: <4B7191D4.4000101@redhat.com>
Date:	Tue, 09 Feb 2010 11:48:20 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Richard Kennedy <richard@....demon.co.uk>
CC:	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Nick Piggin <npiggin@...e.de>, "Theodore Ts'o" <tytso@....edu>
Subject: Re: [PATCH]  fs: buffer_head, remove kmem_cache constructor to reduce
 memory usage under slub

On 02/09/2010 08:29 AM, Richard Kennedy wrote:
> fs: Remove the buffer_head kmem_cache constructor to reduce memory usage
> under slub.
>
> When using slub, having a kmem_cache constructor forces slub to add a
> free pointer to the size of the cached object, which can have a
> significant impact to the number of small objects that can fit into a
> slab.
>
> As buffer_head is relatively small and we can have large numbers of
> them, removing the constructor is a definite win.
>
> On x86_64 removing the constructor gives me 39 objects/slab, 3 more than
> without the patch. And on x86_32 73 objects/slab, which is 9 more.
>
> As alloc_buffer_head() already initializes each new object there is very
> little difference in actual code run.
>
> Signed-off-by: Richard Kennedy<richard@....demon.co.uk>

Reviewed-by: Rik van Riel <riel@...hat.com>

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