linux-kernel - Re: [PATCH 2/2] hugepage: Allow parallelization of the hugepage fault path

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Date:	Fri, 15 Jul 2011 16:06:50 +1000
From:	Anton Blanchard <anton@...ba.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	dwg@....ibm.com, akpm@...ux-foundation.org, hughd@...gle.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] hugepage: Allow parallelization of the hugepage
 fault path

Hi Mel,

> I haven't tested this patch yet but typically how I would test it is
> multiple parallel instances of make func from libhugetlbfs. In
> particular I would be looking out for counter corruption. Has
> something like this been done? I know hugetlb_lock protects the
> counters but the locking in there has turned into a bit of a mess so
> it's easy to miss something.

Thanks for the suggestion and sorry for taking so long. Make check has
the same PASS/FAIL count before and after the patches.

I also ran 16 copies of make func on a large box with 896 HW threads.
Some of the tests that use shared memory were a bit upset, but that
seems to be because we use a static key. It seems the tests were also
fighting over the number of huge pages they wanted the system set to.

It got up to a load average of 13207, and heap-overflow consumed all my
memory, a pretty good effort considering I have over 1TB of it.

After things settled down things were OK, apart from the fact that we
have 20 huge pages unaccounted for:

HugePages_Total:   10000
HugePages_Free:     9980
HugePages_Rsvd:        0
HugePages_Surp:        0

I verified there were no shared memory segments, and no files in the
hugetlbfs filesystem (I double checked by unmounting it).

I can't see how this patch set would cause this. It seems like we can
leak huge pages, perhaps in an error path. Anyway, I'll repost the
patch set for comments.

Anton
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