Re: HugePages_Rsvd leak

From: Mike Kravetz
Date: Wed Apr 08 2015 - 17:16:21 EST

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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