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

[Andrew Perepechko <anserper@ya.ru>]

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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