linux-kernel - Re: HugePages

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Message-ID: <55259A95.3030500@oracle.com>
Date:	Wed, 08 Apr 2015 14:16:05 -0700
From:	Mike Kravetz <mike.kravetz@...cle.com>
To:	Shawn Bohrer <shawn.bohrer@...il.com>, linux-mm@...ck.org
CC:	linux-kernel@...r.kernel.org
Subject: Re: HugePages_Rsvd leak

On 04/08/2015 09:15 AM, Shawn Bohrer wrote:
> I've noticed on a number of my systems that after shutting down my
> application that uses huge pages that I'm left with some pages still
> in HugePages_Rsvd.  It is possible that I still have something using
> huge pages that I'm not aware of but so far my attempts to find
> anything using huge pages have failed.  I've run some simple tests
> using map_hugetlb.c from the kernel source and can see that pages that
> have been reserved but not allocated still show up in
> /proc/<pid>/smaps and /proc/<pid>/numa_maps.  Are there any cases
> where this is not true?

Just a quick question.  Are you using hugetlb filesystem(s)?

If so, you might want to take a look at files residing in the
filesystem(s).  As an experiment, I had a program do a simple
mmap() of a file in a hugetlb filesystem.  The program just
created the mapping, and did not actually fault/allocate any
huge pages.  The result was the reservation (HugePages_Rsvd)
of sufficient huge pages to cover the mapping.  When the program
exited, the reservations remained.  If I remove (unlink) the
file the reservations will be removed.

-- 
Mike Kravetz
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