Re: [PATCH 0/1] mm/hugetlb: fix huge page reservation leak in private mapping error paths
From: Jan Stancek
Date: Thu Oct 20 2016 - 11:47:05 EST
----- Original Message -----
> From: "Mike Kravetz" <mike.kravetz@xxxxxxxxxx>
> To: linux-mm@xxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
> Cc: "Aneesh Kumar K . V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>, "Naoya Horiguchi" <n-horiguchi@xxxxxxxxxxxxx>, "Michal
> Hocko" <mhocko@xxxxxxxx>, "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>, "Hillf Danton"
> <hillf.zj@xxxxxxxxxxxxxxx>, "Dave Hansen" <dave.hansen@xxxxxxxxxxxxxxx>, "Jan Stancek" <jstancek@xxxxxxxxxx>, "Mike
> Kravetz" <mike.kravetz@xxxxxxxxxx>
> Sent: Thursday, 20 October, 2016 5:11:16 AM
> Subject: [PATCH 0/1] mm/hugetlb: fix huge page reservation leak in private mapping error paths
> This issue was discovered by Jan Stancek as described in
> Error paths in hugetlb_cow() and hugetlb_no_page() do not properly clean
> up reservation entries when freeing a newly allocated huge page. This
> issue was introduced with commit 67961f9db8c4 ("mm/hugetlb: fix huge page
> reserve accounting for private mappings). That commit uses the information
> in private mapping reserve maps to determine if a reservation was already
> consumed. This is important in the case of hole punch and truncate as the
> pages are released, but reservation entries are not restored.
> This patch restores the reserve entries in hugetlb_cow and hugetlb_no_page
> such that reserve entries are consistent with the global reservation count.
> The huge page reservation code is quite hard to follow, and this patch
> makes it even more complex. One thought I had was to change the way
> hole punch and truncate work so that private mapping pages are not thrown
> away. This would eliminate the need for this patch as well as 67961f9db8c4.
> It would change the existing semantics (as seen by the user) in this area,
> but I believe the documentation (man pages) say the behavior is unspecified.
> This could be a future change as well as rewriting the existing reservation
> code to make it easier to understand/maintain. Thoughts?
> In any case, this patch addresses the immediate issue.
Just to confirm, I ran this patch on my setup (without the patch from Aneesh)
with libhugetlbfs testsuite in loop for several hours. There were no
ENOMEM/OOM failures, I did not observe resv leak after it finished.
> Mike Kravetz (1):
> mm/hugetlb: fix huge page reservation leak in private mapping error
> mm/hugetlb.c | 66
> 1 file changed, 66 insertions(+)