linux-kernel - Re: [PATCH] Memory management livelock

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Message-Id: <20081002205604.47910d6d.akpm@linux-foundation.org>
Date:	Thu, 2 Oct 2008 20:56:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Mikulas Patocka <mpatocka@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org,
	agk@...hat.com, mbroz@...hat.com, chris@...chsys.com
Subject: Re: [PATCH] Memory management livelock

On Fri, 3 Oct 2008 13:47:21 +1000 Nick Piggin <nickpiggin@...oo.com.au> wrote:

> > I expect there's no solution which avoids blocking the writers at some
> > stage.
> 
> See my other email. Something roughly like this would do the trick
> (hey, it actually boots and runs and does fix the problem too).

It needs exclusion to protect all those temp tags.  Is do_fsync()'s
i_mutex sufficient?  It's qute unobvious (and unmaintainable?) that all
the callers of this stuff are running under that lock.

> It's ugly because we don't have quite the right radix tree operations 
> yet (eg. lookup multiple tags, set tag X if tag Y was set, proper range
> lookups). But the theory is to up-front tag the pages that we need to
> get to disk.

Perhaps some callback-calling radix tree walker.

> Completely no impact or slowdown to any writers (although it does add
> 8 bytes of tags to the radix tree node... but doesn't increase memory
> footprint as such due to slab).

Can we reduce the amount of copy-n-pasting here?
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