linux-kernel - Re: 2.6.26-rc5-mm3: BUG large value for HugePages

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Message-ID: <20080619171644.GC13275@shadowen.org>
Date:	Thu, 19 Jun 2008 18:16:44 +0100
From:	Andy Whitcroft <apw@...dowen.org>
To:	Jon Tollefson <kniht@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	linux-mm@...ck.org, Nick Piggin <npiggin@...e.de>,
	Nishanth Aravamudan <nacc@...ibm.com>,
	Adam Litke <agl@...ux.vnet.ibm.com>
Subject: Re: 2.6.26-rc5-mm3: BUG large value for HugePages_Rsvd

On Thu, Jun 19, 2008 at 11:27:47AM -0500, Jon Tollefson wrote:
> After running some of the libhugetlbfs tests the value for
> /proc/meminfo/HugePages_Rsvd becomes really large.  It looks like it has
> wrapped backwards from zero.
> Below is the sequence I used to run one of the tests that causes this;
> the tests passes for what it is intended to test but leaves a large
> value for reserved pages and that seemed strange to me.
> test run on ppc64 with 16M huge pages

Yes Adam reported that here yesterday, he found it in his hugetlfs testing.
I have done some investigation on it and it is being triggered by a bug in
the private reservation tracking patches.  It is triggered by the hugetlb
test which causes some complex vma splits to occur on a private mapping.

I believe I have the underlying problem nailed and do have some nearly
complete patches for this and they should be in a postable state by
tommorrow.

-apw
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