linux-kernel - Re: [PATCH 3/4] Check whether pages are poisoned before copying

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Message-ID: <20110317162710.GH11094@one.firstfloor.org>
Date:	Thu, 17 Mar 2011 17:27:10 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Huang Ying <ying.huang@...el.com>,
	Jin Dongming <jin.dongming@...css.fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] Check whether pages are poisoned before copying

> What I can tell is with the default khugepaged scan rate, the
> collapse_huge_page will have an impact much smaller than KSM. It could
> have more impact than KSM if you increase khugepaged load to 100% with
> sysfs (because of the more memory that is covered by khugepaged
> compared to only the shared portion of KSM). Then the window gets much
> bigger, but still minor, if you can't trigger it with the testsuite
> it's even less likely to ever happen in practice.

You mean randomly injecting errors?
That tends to be hard and unreliable -- usually we try to have a 
specific tester that is not random.

> Did you try the testsuite with khugepaged at 100% load? I think that's
> good indication if this window has any practical significance.

The measurement is simple: run the workloads and do some dumps
with pagetypes and check if the memory with lots of pages 
has a state that can be handled by memory_failure()

AFAIK  this hasn't been done so far with THP.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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