From: Michal Hocko <mhocko@kernel.org>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jonathan Corbet <corbet@lwn.net>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Vlastimil Babka <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch] mm, thp: always direct reclaim for MADV_HUGEPAGE even when deferred
Date: Thu, 29 Dec 2016 09:24:49 +0100 [thread overview]
Message-ID: <20161229082449.GC29208@dhcp22.suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.10.1612281332320.13632@chino.kir.corp.google.com>
On Wed 28-12-16 13:33:49, David Rientjes wrote:
> On Wed, 28 Dec 2016, Michal Hocko wrote:
>
> > I do care more about _users_ and their _experience_ than what
> > application _writers_ think is the best. This is the whole point
> > of giving the defrag tunable. madvise(MADV_HUGEPAGE) is just a hint to
> > the system that using transparent hugepages is _preferable_, not
> > mandatory. We have an option to allow stalls for those vmas to increase
> > the allocation success rate. We also have tunable to completely ignore
> > it. And we should also have an option to not stall.
> >
>
> The application developer who uses madvise(MADV_HUGEPAGE) is doing so for
> a reason.
and nobody questions that... But the application developer can hardly
forsee the environment where the application runs. And what might
look as a reasonable cost/benefit balance in one setup can turn out
completely wrong in a different one - just consider the fragmentation
which is the primary contributor to stalls. It is hardly predictable
and vary between different workloads/setups a lot. While we have a way
(policty if you will) to tell that madvise should be honored as much
as possible (defrag=madvise) we do not have a way to tell that even
madvised vmas are not worth stalling over because the benefit would not
offset the cost.
> We lack the ability to defragment in the background for all users who
> don't want to block while allowing madvise(MADV_HUGEPAGE) users to block,
> as the changelog for this patch clearly indicates.
And I agree that this is something to be addressed. I just disagree that
this patch is the way how to achieve that.
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2016-12-29 8:24 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-22 0:21 [patch] mm, thp: always direct reclaim for MADV_HUGEPAGE even when deferred David Rientjes
2016-12-22 8:31 ` Kirill A. Shutemov
2016-12-22 10:00 ` Michal Hocko
2016-12-22 21:05 ` David Rientjes
2016-12-23 8:51 ` Michal Hocko
2016-12-23 10:01 ` David Rientjes
2016-12-23 11:18 ` Michal Hocko
2016-12-23 22:46 ` David Rientjes
2016-12-26 9:02 ` Michal Hocko
2016-12-27 0:53 ` David Rientjes
2016-12-27 2:32 ` Kirill A. Shutemov
2016-12-27 9:41 ` Michal Hocko
2016-12-27 21:36 ` David Rientjes
2016-12-28 8:48 ` Michal Hocko
2016-12-28 21:33 ` David Rientjes
2016-12-29 8:24 ` Michal Hocko [this message]
2016-12-30 12:36 ` Mel Gorman
2016-12-30 12:56 ` Michal Hocko
2016-12-30 14:08 ` Mel Gorman
2016-12-30 22:30 ` David Rientjes
2017-01-03 10:37 ` Mel Gorman
2017-01-03 21:57 ` David Rientjes
2017-01-04 10:12 ` Mel Gorman
2017-01-04 21:53 ` David Rientjes
2017-01-02 8:38 ` Vlastimil Babka
2017-01-03 22:44 ` David Rientjes
2017-01-04 8:32 ` Vlastimil Babka
2017-01-04 9:46 ` Michal Hocko
2017-01-04 22:04 ` David Rientjes
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