linux-kernel - Re: [rfc 3/4] mm, page_alloc: avoid expensive reclaim when compaction may not succeed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 6 Sep 2019 13:16:48 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
cc:     Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [rfc 3/4] mm, page_alloc: avoid expensive reclaim when compaction
 may not succeed

On Thu, 5 Sep 2019, Mike Kravetz wrote:

> I don't have a specific test for this.  It is somewhat common for people
> to want to allocate "as many hugetlb pages as possible".  Therefore, they
> will try to allocate more pages than reasonable for their environment and
> take what they can get.  I 'tested' by simply creating some background
> activity and then seeing how many hugetlb pages could be allocated.  Of
> course, many tries over time in a loop.
> 
> This patch did not cause premature allocation failures in my limited testing.
> The number of pages which could be allocated with and without patch were
> pretty much the same.
> 
> Do note that I tested on top of Andrew's tree which contains this series:
> http://lkml.kernel.org/r/20190806014744.15446-1-mike.kravetz@oracle.com
> Patch 3 in that series causes allocations to fail sooner in the case of
> COMPACT_DEFERRED:
> http://lkml.kernel.org/r/20190806014744.15446-4-mike.kravetz@oracle.com
> 
> hugetlb allocations have the __GFP_RETRY_MAYFAIL flag set.  They are willing
> to retry and wait and callers are aware of this.  Even though my limited
> testing did not show regressions caused by this patch, I would prefer if the
> quick exit did not apply to __GFP_RETRY_MAYFAIL requests.

Good!  I think that is the ideal way of handling it: we can specify the 
preference to actually loop and retry (but still eventually fail) for 
hugetlb allocations specifically for this patch by testing for 
__GFP_RETRY_MAYFAIL.

I can add that to the formal proposal of patches 3 and 4 in this series 
assuming we get 5.3 settled by applying the reverts in patches 1 and 2 so 
that we don't cause various versions of Linux to have different default 
and madvise allocation policies wrt NUMA.