Re: [PATCH 0/5] Obey mark_page_accessed hint given by filesystemsv3r1

From: Andrew Perepechko
Date: Fri May 17 2013 - 14:43:28 EST

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)


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 -- .
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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