linux-kernel - Re: [PATCH]dquot: do full inode dirty in allocating space

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Date:	Wed, 25 Aug 2010 07:26:09 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Jan Kara <jack@...e.cz>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Shi, Alex" <alex.shi@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH]dquot: do full inode dirty in allocating space

On Tue, Aug 24, 2010 at 10:23:59PM +0800, Jan Kara wrote:
>   Hi,
> 
> On Fri 20-08-10 16:49:43, Shaohua Li wrote:
> > Alex Shi found a regression when doing ffsb test. The test has several threads,
> > and each thread creates a small file, write to it and then delete it. ffsb
> > reports about 20% regression and Alex bisected it to 43d2932d88e4. The test
> > will call __mark_inode_dirty 3 times. without this commit, we only take
> > inode_lock one time, while with it, we take the lock 3 times with flags (
> > I_DIRTY_SYNC,I_DIRTY_PAGES,I_DIRTY). Perf shows the lock contention increased
> > too much. Below proposed patch fixes it.
>   Thanks for the analysis and the patch!  With which filesystem have you
> measured the results? And what kind of machine it was?
it's ext3 and 24 CPU system with two sockets.
 
> > fs is allocating blocks, which usually means file writes and the inode
> > will be dirtied soon. We fully dirty the inode to reduce some inode_lock
> > contention in several calls of __mark_inode_dirty.
>   Well, this is rather a workaround for a poor handling of inode dirty
> bits. BTW, I think Nick's VFS scalability patches address inode_lock
> contention as well so with them the contention you see should be reduced.
yep, the VFS scalability patch might reduce this.

>   Anyway, I will take this patch for the time before inode_lock
> contention improves and add a proper comment about this before
> mark_inode_dirty.
Thanks.
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