linux-kernel - Re: [PATCH] sysfs: Cache the last sysfs_dirent to improve readdir scalability

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Date:	Fri, 1 Jan 2010 16:33:53 +0100
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Airlie <airlied@...ux.ie>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg KH <greg@...ah.com>, Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH] sysfs: Cache the last sysfs_dirent to improve readdir
 scalability

On Fri, Jan 01, 2010 at 05:58:00AM -0800, Eric W. Biederman wrote:
> 
> When sysfs_readdir stops short we now cache the next sysfs_dirent to
> return to user space in filp->private_data.  There is no impact on the
> rest of sysfs by doing this and in the common case it allows us to
> pick up exactly where we left off with no seeking.
> 
> Additionally I drop and regrab the sysfs_mutex around filldir to avoid
> a page fault arbitrarily increasing the hold time on the sysfs_mutex.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@...stanetworks.com>
> ---
> 
> I haven't stressed this patch but it is sound in principle, and is a
> general sysfs improvement, regardless of any locking issues.

I've slapped it ontop of v2.6.33-rc2-249-gcd6e125 here and the circular
locking warning is gone. I'll keep an eye on it in the next couple of
days, just in case.

Tested-by: Borislav Petkov <petkovbb@...il.com>

-- 
Regards/Gruss,
    Boris.
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