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Re: [PATCH 00/31] Move LRU page reclaim from zones to nodes v8

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On Fri, Jul 01, 2016 at 04:37:15PM +0100, Mel Gorman wrote:
> Previous releases double accounted LRU stats on the zone and the node
> because it was required by should_reclaim_retry. The last patch in the
> series removes the double accounting. It's not integrated with the series
> as reviewers may not like the solution. If not, it can be safely dropped
> without a major impact to the results.
....
> tiobench on ext4
> ----------------

[snip other tests on ext4 which show good results]

.....
> This series is not without its hazards. There are at least three areas
> that I'm concerned with even though I could not reproduce any problems in
> that area.
> 
> 1. Reclaim/compaction is going to be affected because the amount of reclaim is
>    no longer targetted at a specific zone. Compaction works on a per-zone basis
>    so there is no guarantee that reclaiming a few THP's worth page pages will
>    have a positive impact on compaction success rates.
> 
> 2. The Slab/LRU reclaim ratio is affected because the frequency the shrinkers
>    are called is now different. This may or may not be a problem but if it
>    is, it'll be because shrinkers are not called enough and some balancing
>    is required.

Given that XFS has a much more complex set of shrinkers and has a
much more finely tuned balancing between LRU and shrinker reclaim,
I'd be interested to see if you get the same results on XFS for the
tests you ran on ext4. It might also be worth running some highly
concurrent inode cache benchmarks (e.g. the 50-million inode, 16-way
concurrent fsmark tests) to see what impact heavy slab cache
pressure has on shrinker behaviour and system balance...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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[PATCH 00/31] Move LRU page reclaim from zones to nodes v8 Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:40 +0200
  [PATCH 06/31] mm, vmscan: make kswapd reclaim in terms of nodes Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:40 +0200
  [PATCH 09/31] mm, vmscan: by default have direct reclaim only shrink once per node Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:40 +0200
  [PATCH 10/31] mm, vmscan: remove duplicate logic clearing node congestion and dirty state Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:40 +0200
  [PATCH 07/31] mm, vmscan: remove balance gap Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:40 +0200
  [PATCH 02/31] mm, vmscan: move lru_lock to the node Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:40 +0200
  [PATCH 05/31] mm, vmscan: have kswapd only scan based on the highest requested zone Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:40 +0200
  [PATCH 19/31] mm: move vmscan writes and file write accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 17/31] mm: rename NR_ANON_PAGES to NR_ANON_MAPPED Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 30/31] mm, vmstat: print node-based stats in zoneinfo file Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 31/31] mm, vmstat: Remove zone and node double accounting by approximating retries Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 22/31] mm: convert zone_reclaim to node_reclaim Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 26/31] mm, page_alloc: remove fair zone allocation policy Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 28/31] mm: vmstat: replace __count_zone_vm_events with a zone id equivalent Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 21/31] mm, page_alloc: Wake kswapd based on the highest eligible zone Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 20/31] mm, vmscan: only wakeup kswapd once per node for the requested classzone Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 14/31] mm, workingset: make working set detection node-aware Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 18/31] mm: move most file-based accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 23/31] mm, vmscan: Avoid passing in classzone_idx unnecessarily to shrink_node Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 27/31] mm: page_alloc: cache the last node whose dirty limit is reached Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 11/31] mm: vmscan: do not reclaim from kswapd if there is any eligible zone Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 12/31] mm, vmscan: make shrink_node decisions more node-centric Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 15/31] mm, page_alloc: consider dirtyable memory in terms of nodes Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 24/31] mm, vmscan: Avoid passing in classzone_idx unnecessarily to compaction_ready Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 13/31] mm, memcg: move memcg limit enforcement from zones to nodes Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 25/31] mm, vmscan: add classzone information to tracepoints Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 29/31] mm: vmstat: account per-zone stalls and pages skipped during reclaim Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  [PATCH 16/31] mm: move page mapped accounting to the node Mel Gorman <mgorman@techsingularity.net> - 2016-07-01 17:50 +0200
  Re: [PATCH 00/31] Move LRU page reclaim from zones to nodes v8 Dave Chinner <david@fromorbit.com> - 2016-07-08 01:30 +0200
    Re: [PATCH 00/31] Move LRU page reclaim from zones to nodes v8 Mel Gorman <mgorman@techsingularity.net> - 2016-07-08 12:00 +0200

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