linux-kernel - Re: HugePages

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Date:	Wed, 8 Apr 2015 16:42:42 -0500
From:	Shawn Bohrer <shawn.bohrer@...il.com>
To:	Mike Kravetz <mike.kravetz@...cle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: HugePages_Rsvd leak

On Wed, Apr 08, 2015 at 02:16:05PM -0700, Mike Kravetz wrote:
> 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)?

I can't say for sure that nothing is using hugetlbfs. It is mounted
but as far as I can tell on the affected system(s) it is empty.

[root@...106 ~]# grep hugetlbfs /proc/mounts
hugetlbfs /dev/hugepages hugetlbfs rw,relatime 0 0
[root@...106 ~]# ls -al /dev/hugepages/
total 0
drwxr-xr-x  2 root root    0 Apr  8 16:22 .
drwxr-xr-x 16 root root 4360 Apr  8 03:53 ..
[root@...106 ~]# lsof | grep hugepages

> 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.

That makes sense but I don't think it is the issue here.

Thanks,
Shawn
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