From: David Rientjes <rientjes@google.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>, Mel Gorman <mgorman@suse.de>,
Vlastimil Babka <vbabka@suse.cz>,
Andrea Argangeli <andrea@kernel.org>,
Zi Yan <zi.yan@cs.rutgers.edu>,
Stefan Priebe - Profihost AG <s.priebe@profihost.ag>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
Stable tree <stable@vger.kernel.org>
Subject: Re: [PATCH 1/2] mm: thp: relax __GFP_THISNODE for MADV_HUGEPAGE mappings
Date: Mon, 22 Oct 2018 13:54:33 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.21.1810221346130.120157@chino.kir.corp.google.com> (raw)
In-Reply-To: <20181015231953.GC30832@redhat.com>
On Mon, 15 Oct 2018, Andrea Arcangeli wrote:
> > On Mon, 15 Oct 2018 15:30:17 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:
> > > Would it be possible to test with my
> > > patch[*] that does not try reclaim to address the thrashing issue?
> >
> > Yes please.
>
> It'd also be great if a testcase reproducing the 40% higher access
> latency (with the one liner original fix) was available.
>
I never said 40% higher access latency, I said 40% higher fault latency.
The higher access latency is 13.9% as measured on Haswell.
The test case is rather trivial: fragment all memory with order-4 memory
to replicate a fragmented local zone, use sched_setaffinity() to bind to
that node, and fault a reasonable number of hugepages (128MB, 256,
whatever). The cost of faulting remotely in this case was measured to be
40% higher than falling back to local small pages. This occurs quite
obviously because you are thrashing the remote node trying to allocate
thp.
> We don't have a testcase for David's 40% latency increase problem, but
> that's likely to only happen when the system is somewhat low on memory
> globally.
Well, yes, but that's most of our systems. We can't keep around gigabytes
of memory free just to work around this patch. Removing __GFP_THISNODE to
avoid thrashing the local node obviously will incur a substantial
performance degradation if you thrash the remote node as well. This
should be rather straight forward.
> When there's 75% or more of the RAM free (not even allocated as easily
> reclaimable pagecache) globally, you don't expect to hit heavy
> swapping.
>
I agree there is no regression introduced by your patch when 75% of memory
is free.
> The 40% THP allocation latency increase if you use MADV_HUGEPAGE in
> such window where all remote zones are fully fragmented is somehow
> lesser of a concern in my view (plus there's the compact deferred
> logic that should mitigate that scenario). Furthermore it is only a
> concern for page faults in MADV_HUGEPAGE ranges. If MADV_HUGEPAGE is
> set the userland allocation is long lived, so such higher allocation
> latency won't risk to hit short lived allocations that don't set
> MADV_HUGEPAGE (unless madvise=always, but that's not the default
> precisely because not all allocations are long lived).
>
> If the MADV_HUGEPAGE using library was freely available it'd also be
> nice.
>
You scan your mappings for .text segments, map a hugepage-aligned region
sufficient in size, mremap() to that region, and do MADV_HUGEPAGE.
next prev parent reply other threads:[~2018-10-22 20:54 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-25 12:03 [PATCH 0/2] thp nodereclaim fixes Michal Hocko
2018-09-25 12:03 ` [PATCH 1/2] mm: thp: relax __GFP_THISNODE for MADV_HUGEPAGE mappings Michal Hocko
2018-09-25 12:20 ` Mel Gorman
2018-09-25 12:30 ` Michal Hocko
2018-10-04 20:16 ` David Rientjes
2018-10-04 21:10 ` Andrea Arcangeli
2018-10-04 23:05 ` David Rientjes
2018-10-06 3:19 ` Andrea Arcangeli
2018-10-05 7:38 ` Mel Gorman
2018-10-05 20:35 ` David Rientjes
2018-10-05 23:21 ` Andrea Arcangeli
2018-10-08 20:41 ` David Rientjes
2018-10-09 9:48 ` Mel Gorman
2018-10-09 12:27 ` Michal Hocko
2018-10-09 13:00 ` Mel Gorman
2018-10-09 14:25 ` Michal Hocko
2018-10-09 15:16 ` Mel Gorman
2018-10-09 23:03 ` Andrea Arcangeli
2018-10-10 21:19 ` David Rientjes
2018-10-15 22:30 ` David Rientjes
2018-10-15 22:44 ` Andrew Morton
2018-10-15 23:19 ` Andrea Arcangeli
2018-10-22 20:54 ` David Rientjes [this message]
2018-10-16 7:46 ` Mel Gorman
2018-10-16 22:37 ` Andrew Morton
2018-10-16 23:11 ` Andrea Arcangeli
2018-10-16 23:16 ` Andrew Morton
2018-10-17 7:08 ` Michal Hocko
2018-10-17 9:00 ` Mel Gorman
2018-10-22 21:04 ` David Rientjes
2018-10-23 1:27 ` Zi Yan
2018-10-28 21:45 ` David Rientjes
2018-10-23 7:57 ` Mel Gorman
2018-10-23 8:38 ` Mel Gorman
2018-10-15 22:57 ` Andrea Arcangeli
2018-10-22 20:45 ` David Rientjes
2018-10-09 22:17 ` David Rientjes
2018-10-09 22:51 ` Andrea Arcangeli
2018-10-10 7:54 ` Vlastimil Babka
2018-10-10 21:00 ` David Rientjes
2018-10-09 13:08 ` Vlastimil Babka
2018-10-09 22:21 ` Andrea Arcangeli
2018-10-29 5:17 ` Balbir Singh
2018-10-29 9:00 ` Michal Hocko
2018-10-29 9:42 ` Balbir Singh
2018-10-29 10:08 ` Michal Hocko
2018-10-29 10:56 ` Andrea Arcangeli
2018-09-25 12:03 ` [PATCH 2/2] mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask Michal Hocko
2018-09-26 13:30 ` Kirill A. Shutemov
2018-09-26 14:17 ` Michal Hocko
2018-09-26 14:22 ` Michal Hocko
2018-10-19 2:11 ` Andrew Morton
2018-10-19 8:06 ` Michal Hocko
2018-10-22 13:27 ` Vlastimil Babka
2018-10-24 23:17 ` Andrew Morton
2018-10-25 4:56 ` Vlastimil Babka
2018-10-25 16:14 ` Michal Hocko
2018-10-25 16:18 ` Andrew Morton
2018-10-25 16:45 ` Michal Hocko
2018-10-22 13:15 ` Vlastimil Babka
2018-10-22 13:30 ` Michal Hocko
2018-10-22 13:35 ` Vlastimil Babka
2018-10-22 13:46 ` Michal Hocko
2018-10-22 13:53 ` Vlastimil Babka
2018-10-04 20:17 ` David Rientjes
2018-10-04 21:49 ` Zi Yan
2018-10-09 12:36 ` Michal Hocko
2018-09-26 13:08 ` linux-mm@ archive on lore.kernel.org (Was: [PATCH 0/2] thp nodereclaim fixes) Kirill A. Shutemov
2018-09-26 13:14 ` Michal Hocko
2018-09-26 22:22 ` Andrew Morton
2018-09-26 23:08 ` Mel Gorman
2018-09-27 0:47 ` Konstantin Ryabitsev
2018-09-26 15:25 ` Konstantin Ryabitsev
2018-09-27 11:30 ` Kirill A. Shutemov
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