linux-ext4 - Re: [PATCH 0/5] Obey mark_page_accessed hint given by filesystems v3r1

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Message-ID: <519678A2.5040509@ya.ru>
Date:	Fri, 17 May 2013 22:36:18 +0400
From:	Andrew Perepechko <anserper@...ru>
To:	Mel Gorman <mgorman@...e.de>
CC:	Alexey Lyahkov <alexey.lyashkov@...il.com>,
	Robin Dong <sanbai@...bao.com>, Theodore Tso <tytso@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Bernd Schubert <bernd.schubert@...tmail.fm>,
	David Howells <dhowells@...hat.com>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux-ext4 <linux-ext4@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH 0/5] Obey mark_page_accessed hint given by filesystems
 v3r1

Mel, thank you very much for the patches!

Unfortunately, it may take some time for us to test them,
because currently we depend very much on an older (2.6.32-based)
kernel.

Andrew

On 05/17/2013 01:48 PM, Mel Gorman wrote:
> This series could still do with some Tested-by's from the original bug
> reporters. Andrew Perepechko?
>
> Changelog since V2
> o Beef up the comments in a number of places			(akpm)
> o Remove lru parameter from __lru_cache_add, lru_cache_add_lru	(akpm)
> o Use congestion_wait instead of wait_on_page_writeback in case
>    of storage disconnects					(akpm)
>
> Changelog since V1
> o Add tracepoint to model age of page types			(mel)
>
> Andrew Perepechko reported a problem whereby pages are being prematurely
> evicted as the mark_page_accessed() hint is ignored for pages that are
> currently on a pagevec -- http://www.spinics.net/lists/linux-ext4/msg37340.html .
> Alexey Lyahkov and Robin Dong have also reported problems recently that
> could be due to hot pages reaching the end of the inactive list too quickly
> and be reclaimed.
>
> Rather than addressing this on a per-filesystem basis, this series aims
> to fix the mark_page_accessed() interface by deferring what LRU a page
> is added to pagevec drain time and allowing mark_page_accessed() to call
> SetPageActive on a pagevec page.
>
> Patch 1 adds two tracepoints for LRU page activation and insertion. Using
> 	these processes it's possible to build a model of pages in the
> 	LRU that can be processed offline.
>
> Patch 2 defers making the decision on what LRU to add a page to until when
> 	the pagevec is drained.
>
> Patch 3 searches the local pagevec for pages to mark PageActive on
> 	mark_page_accessed. The changelog explains why only the local
> 	pagevec is examined.
>
> Patches 4 and 5 tidy up the API.
>
> postmark, a dd-based test and fs-mark both single and threaded mode were
> run but none of them showed any performance degradation or gain as a result
> of the patch.
>
> Using patch 1, I built a *very* basic model of the LRU to examine
> offline what the average age of different page types on the LRU were in
> milliseconds. Of course, capturing the trace distorts the test as it's
> written to local disk but it does not matter for the purposes of this test.
> The average age of pages in milliseconds were
>
> 				    vanilla deferdrain
> Average age mapped anon:               1454       1250
> Average age mapped file:             127841     155552
> Average age unmapped anon:               85        235
> Average age unmapped file:            73633      38884
> Average age unmapped buffers:         74054     116155
>
> The LRU activity was mostly files which you'd expect for a dd-based
> workload. Note that the average age of buffer pages is increased by the
> series and it is expected this is due to the fact that the buffer pages are
> now getting added to the active list when drained from the pagevecs. Note
> that the average age of the unmapped file data is decreased as they are
> still added to the inactive list and are reclaimed before the buffers. There
> is no guarantee this is a universal win for all workloads and it would be
> nice if the filesystem people gave some thought as to whether this decision
> is generally a win or a loss.
>
>   fs/cachefiles/rdwr.c           |  30 +++---------
>   fs/nfs/dir.c                   |   7 +--
>   include/linux/pagevec.h        |  34 +-------------
>   include/linux/swap.h           |  11 +++--
>   include/trace/events/pagemap.h |  89 +++++++++++++++++++++++++++++++++++
>   mm/rmap.c                      |   7 +--
>   mm/swap.c                      | 103 ++++++++++++++++++++++++++---------------
>   mm/vmscan.c                    |   4 +-
>   8 files changed, 176 insertions(+), 109 deletions(-)
>   create mode 100644 include/trace/events/pagemap.h
>

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