From: Steve Capper <steve.capper@linaro.org>
To: Joern Engel <joern@logfs.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 1/2] hugetlb: properly account rss
Date: Wed, 3 Jul 2013 14:41:19 +0100 [thread overview]
Message-ID: <20130703134118.GA4978@linaro.org> (raw)
In-Reply-To: <1371581225-27535-2-git-send-email-joern@logfs.org>
On Tue, Jun 18, 2013 at 02:47:04PM -0400, Joern Engel wrote:
> When moving a program from mmap'ing small pages to mmap'ing huge pages,
> a remarkable drop in rss ensues. For some reason hugepages were never
> accounted for in rss, which in my book is a clear bug. Sadly this bug
> has been present in hugetlbfs since it was merged back in 2002. There
> is every chance existing programs depend on hugepages not being counted
> as rss.
>
> I think the correct solution is to fix the bug and wait for someone to
> complain. It is just as likely that noone cares - as evidenced by the
> fact that noone seems to have noticed for ten years.
>
> Signed-off-by: Joern Engel <joern@logfs.org>
> ---
> mm/hugetlb.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
Hi,
This patch has caused a few warnings for me today when it was integrated into
linux-next. The libhugetlbfs test suite gave me:
[ 94.320661] BUG: Bad rss-counter state mm:ffff880119461040 idx:1 val:-512
[ 94.330346] BUG: Bad rss-counter state mm:ffff880119460680 idx:1 val:-2560
[ 94.341746] BUG: Bad rss-counter state mm:ffff880119460d00 idx:1 val:-512
[ 94.347518] BUG: Bad rss-counter state mm:ffff880119460d00 idx:1 val:-512
[ 94.415203] BUG: Bad rss-counter state mm:ffff8801194f9040 idx:1 val:-1024
[ ...]
I think I've found the cause; MAP_SHARED mappings.
alloc_huge_page and __unmap_hugepage_range are called for shared pages. Also,
__unmap_hugepage_range is called more times than alloc_huge_page (which makes
sense as multiple views of a shared mapping are unmapped) leading to negative
counter values.
Excluding VM_SHARED VMAs from the counter increment/decrement stopped the
warnings for me. Although this may not be the best way to address the issue.
Cheers,
--
Steve
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next prev parent reply other threads:[~2013-07-03 13:41 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-18 18:47 [PATCH 0/2] hugetlb fixes Joern Engel
2013-06-18 18:47 ` [PATCH 1/2] hugetlb: properly account rss Joern Engel
2013-06-28 22:03 ` Andrew Morton
2013-07-03 13:41 ` Steve Capper [this message]
2013-07-03 14:55 ` Steve Capper
2013-06-18 18:47 ` [PATCH 2/2] mmap: allow MAP_HUGETLB for hugetlbfs files Joern Engel
2013-06-19 1:22 ` Jianguo Wu
2013-06-19 16:25 ` [PATCH] mmap: allow MAP_HUGETLB for hugetlbfs files v2 Jörn Engel
2013-06-20 1:31 ` Jianguo Wu
2013-06-19 16:25 ` [PATCH 2/2] mmap: allow MAP_HUGETLB for hugetlbfs files Jörn Engel
2013-06-18 18:50 ` [PATCH 0/2] hugetlb fixes Jörn Engel
2013-06-18 20:27 ` Andrew Morton
2013-06-18 20:04 ` Jörn Engel
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