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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)
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.

  reply index

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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