linux-kernel - Re: [PATCH] Optimize wait_sb

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Message-ID: <20130628052352.GA9047@dastard>
Date:	Fri, 28 Jun 2013 15:23:52 +1000
From:	Dave Chinner <david@...morbit.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Theodore Ts'o <tytso@....edu>, Al Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	tux3@...3.org
Subject: Re: [PATCH] Optimize wait_sb_inodes()

On Fri, Jun 28, 2013 at 09:30:17AM +0900, OGAWA Hirofumi wrote:
> Theodore Ts'o <tytso@....edu> writes:
> 
> > On Fri, Jun 28, 2013 at 08:37:40AM +0900, OGAWA Hirofumi wrote:
> >> 
> >> Well, anyway, it is simple. This issue was came as the performance
> >> regression when I was experimenting to use kernel bdi flusher from own
> >> flusher. The issue was sync(2) like I said.  And this was just I
> >> couldn't solve this issue by tux3 side unlike other optimizations.
> >
> > A performance regression using fsstress?  That's not a program
> > intended to be a useful benchmark for measuring performance.
> 
> Right. fsstress is used as stress tool for me too as part of CI, with
> background vmstat 1. Anyway, it is why I noticed this.
> 
> I agree it would not be high priority. But I don't think we should stop
> to optimize it.

But you're not proposing any sort of optimisation at all - you're
simply proposing to hack around the problem so you don't have to
care about it. The VFS is a shared resource - it has to work well
for everyone - and that means we need to fix problems and not ignore
them.

As I said, wait_sb_inodes() is fixable. I'm not fixing for tux3,
though - I'm fixing it because it's causing soft lockups on XFS and
ext4 in 3.10-rc6:

https://lkml.org/lkml/2013/6/27/772

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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