From: Taras Kondratiuk <takondra@cisco.com>
To: Michal Hocko <mhocko@kernel.org>, vcaputo@pengaru.com
Cc: linux-mm@kvack.org, xe-linux-external@cisco.com,
Ruslan Ruslichenko <rruslich@cisco.com>,
linux-kernel@vger.kernel.org
Subject: Re: Detecting page cache trashing state
Date: Fri, 15 Sep 2017 16:40:00 -0700 [thread overview]
Message-ID: <150551880069.3028.17086017203169162136@takondra-t460s> (raw)
In-Reply-To: <20170915212028.GZ9731@shells.gnugeneration.com>
Quoting vcaputo@pengaru.com (2017-09-15 14:20:28)
> On Fri, Sep 15, 2017 at 04:36:19PM +0200, Michal Hocko wrote:
> > On Thu 14-09-17 17:16:27, Taras Kondratiuk wrote:
> > > Hi
> > >
> > > In our devices under low memory conditions we often get into a trashing
> > > state when system spends most of the time re-reading pages of .text
> > > sections from a file system (squashfs in our case). Working set doesn't
> > > fit into available page cache, so it is expected. The issue is that
> > > OOM killer doesn't get triggered because there is still memory for
> > > reclaiming. System may stuck in this state for a quite some time and
> > > usually dies because of watchdogs.
> > >
> > > We are trying to detect such trashing state early to take some
> > > preventive actions. It should be a pretty common issue, but for now we
> > > haven't find any existing VM/IO statistics that can reliably detect such
> > > state.
> > >
> > > Most of metrics provide absolute values: number/rate of page faults,
> > > rate of IO operations, number of stolen pages, etc. For a specific
> > > device configuration we can determine threshold values for those
> > > parameters that will detect trashing state, but it is not feasible for
> > > hundreds of device configurations.
> > >
> > > We are looking for some relative metric like "percent of CPU time spent
> > > handling major page faults". With such relative metric we could use a
> > > common threshold across all devices. For now we have added such metric
> > > to /proc/stat in our kernel, but we would like to find some mechanism
> > > available in upstream kernel.
> > >
> > > Has somebody faced similar issue? How are you solving it?
> >
> > Yes this is a pain point for a _long_ time. And we still do not have a
> > good answer upstream. Johannes has been playing in this area [1].
> > The main problem is that our OOM detection logic is based on the ability
> > to reclaim memory to allocate new memory. And that is pretty much true
> > for the pagecache when you are trashing. So we do not know that
> > basically whole time is spent refaulting the memory back and forth.
> > We do have some refault stats for the page cache but that is not
> > integrated to the oom detection logic because this is really a
> > non-trivial problem to solve without triggering early oom killer
> > invocations.
> >
> > [1] http://lkml.kernel.org/r/20170727153010.23347-1-hannes@cmpxchg.org
>
> For desktop users running without swap, couldn't we just provide a kernel
> setting which marks all executable pages as unevictable when first faulted
> in? Then at least thrashing within the space occupied by executables and
> shared libraries before eventual OOM would be avoided, and only the
> remaining file-backed non-executable pages would be thrashable.
>
> On my swapless laptops I'd much rather have OOM killer kick in immediately
> rather than wait for a few minutes of thrashing to pass while the bogged
> down system crawls through depleting what's left of technically reclaimable
> memory. It's much improved on modern SSDs, but still annoying.
Usually a significant part of executable is used rarely or only once
during initialization. Pinning all executable pages forever will waste
a lot of memory.
next prev parent reply other threads:[~2017-09-15 23:40 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-15 0:16 Detecting page cache trashing state Taras Kondratiuk
2017-09-15 11:55 ` Zdenek Kabelac
2017-09-15 14:22 ` Daniel Walker
2017-09-15 16:38 ` Taras Kondratiuk
2017-09-15 17:31 ` Daniel Walker
2017-09-15 14:36 ` Michal Hocko
2017-09-15 17:28 ` Taras Kondratiuk
2017-09-18 16:34 ` Johannes Weiner
2017-09-19 10:55 ` [PATCH 1/3] sched/loadavg: consolidate LOAD_INT, LOAD_FRAC macros kbuild test robot
2017-09-19 11:02 ` kbuild test robot
2017-09-28 15:49 ` Detecting page cache trashing state Ruslan Ruslichenko -X (rruslich - GLOBALLOGIC INC at Cisco)
2017-10-25 16:53 ` Daniel Walker
2017-10-25 17:54 ` Johannes Weiner
2017-10-27 20:19 ` Ruslan Ruslichenko -X (rruslich - GLOBALLOGIC INC at Cisco)
2017-11-20 19:40 ` Ruslan Ruslichenko -X (rruslich - GLOBALLOGIC INC at Cisco)
2017-11-27 2:18 ` Minchan Kim
2017-10-26 3:53 ` vinayak menon
2017-10-27 20:29 ` Ruslan Ruslichenko -X (rruslich - GLOBALLOGIC INC at Cisco)
2017-09-15 21:20 ` vcaputo
2017-09-15 23:40 ` Taras Kondratiuk [this message]
2017-09-18 5:55 ` Michal Hocko
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