linux-kernel - Re: Linux 2.6.29

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Message-ID: <alpine.LFD.2.00.0903251341050.3032@localhost.localdomain>
Date:	Wed, 25 Mar 2009 13:45:43 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Theodore Tso <tytso@....edu>
cc:	Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	David Rees <drees76@...il.com>, Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29



On Wed, 25 Mar 2009, Theodore Tso wrote:
> 
> Now, there are three ways of solving this problem.

You seem to disregard the "write in the right order" approach. Or is that 
your:

> The third potential solution we can try doing is to make some tuning
> adjustments to the VM so that we start pushing out these data blocks
> much more aggressively out to the disk.

Yes. but at least one problem is, as mentioned, that when the VM calls 
writepage[s]() to start async writeback, many filesystems do seem to just 
_block_ on it.

So the VM has a really hard time doing anything sanely early - the 
filesystems seem to take a perverse pleasure in synchronizing things using 
blocking semaphores.

			Linus
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