linux-kernel - Re: [patch 00/19] VM pageout scalability improvements

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Message-ID: <20080103170035.105d22c8@cuia.boston.redhat.com>
Date:	Thu, 3 Jan 2008 17:00:35 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Eric Whitney <eric.whitney@...com>
Subject: Re: [patch 00/19] VM pageout scalability improvements

On Thu, 03 Jan 2008 12:13:32 -0500
Lee Schermerhorn <Lee.Schermerhorn@...com> wrote:

> Yes, but the problem, when it occurs, is very awkward.  The system just
> hangs for hours/days spinning on the reverse mapping locks--in both
> page_referenced() and try_to_unmap().  No pages get reclaimed and NO OOM
> kill occurs because we never get that far.  So, I'm not sure I'd call
> any OOM kills resulting from this patch as "false".  The memory is
> effectively nonreclaimable.   Now, I think that your anon pages SEQ
> patch will eliminate the contention in page_referenced[_anon](), but we
> could still hang in try_to_unmap().

I am hoping that Nick's ticket spinlocks will fix this problem.

Would you happen to have any test cases for the above problem that
I could use to reproduce the problem and look for an automatic fix?

Any fix that requires the sysadmin to tune things _just_ right seems
too dangerous to me - especially if a change in the workload can
result in the system doing exactly the wrong thing...

The idea is valid, but it just has to work automagically.

Btw, if page_referenced() is called less, the locks that try_to_unmap()
also takes should get less contention.

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