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

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Message-ID: <20100824143011.GF3713@quack.suse.cz>
Date:	Tue, 24 Aug 2010 16:30:11 +0200
From:	Jan Kara <jack@...e.cz>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	linux-kernel@...r.kernel.org, jack@...e.cz, alex.shi@...el.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH]dquot: do full inode dirty in allocating space

On Tue 24-08-10 16:23:59, 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?
> 
> > 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.
>   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.
  Attached is a version of the patch that is in my tree now.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR

View attachment "0001-dquot-do-full-inode-dirty-in-allocating-space.patch" of type "text/x-patch" (1775 bytes)