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From: Balbir Singh <bsingharora@gmail.com>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Linux-MM <linux-mm@kvack.org>, Rik van Riel <riel@surriel.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Johannes Weiner <hannes@cmpxchg.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 00/27] Move LRU page reclaim from zones to nodes v7
Date: Mon, 27 Jun 2016 22:48:03 +1000	[thread overview]
Message-ID: <57712083.8060500@gmail.com> (raw)
In-Reply-To: <20160624075059.GC1868@techsingularity.net>



On 24/06/16 17:50, Mel Gorman wrote:
> On Fri, Jun 24, 2016 at 04:35:45PM +1000, Balbir Singh wrote:
>>> 1. The residency of a page partially depends on what zone the page was
>>>    allocated from.  This is partially combatted by the fair zone allocation
>>>    policy but that is a partial solution that introduces overhead in the
>>>    page allocator paths.
>>>
>>> 2. Currently, reclaim on node 0 behaves slightly different to node 1. For
>>>    example, direct reclaim scans in zonelist order and reclaims even if
>>>    the zone is over the high watermark regardless of the age of pages
>>>    in that LRU. Kswapd on the other hand starts reclaim on the highest
>>>    unbalanced zone. A difference in distribution of file/anon pages due
>>>    to when they were allocated results can result in a difference in 
>>>    again. While the fair zone allocation policy mitigates some of the
>>>    problems here, the page reclaim results on a multi-zone node will
>>>    always be different to a single-zone node.
>>>    it was scheduled on as a result.
>>>
>>> 3. kswapd and the page allocator scan zones in the opposite order to
>>>    avoid interfering with each other but it's sensitive to timing.  This
>>>    mitigates the page allocator using pages that were allocated very recently
>>>    in the ideal case but it's sensitive to timing. When kswapd is allocating
>>>    from lower zones then it's great but during the rebalancing of the highest
>>>    zone, the page allocator and kswapd interfere with each other. It's worse
>>>    if the highest zone is small and difficult to balance.
>>>
>>> 4. slab shrinkers are node-based which makes it harder to identify the exact
>>>    relationship between slab reclaim and LRU reclaim.
>>>
>>
>> Sorry, I am late in reading the thread and the patches, but I am trying to understand
>> the key benefits?
> 
> The key benefits were outlined at the beginning of the changelog. The
> one that is missing is the large overhead from the fair zone allocation
> policy which can be removed safely by the feature. The benefit to page
> allocator micro-benchmarks is outlined in the series introduction.

I did look at them, but between 1 to 4, it seemed like the largest benefit
was mm cleanup and better behaviour of reclaim on node 0.

> 
>> I know that
>> zones have grown to be overloaded to mean many things now. What is the contention impact
>> of moving the LRU from zone to nodes?
> 
> Expected to be minimal. On NUMA machines, most nodes have only one zone.
> On machines with multiple zones, the lock per zone is not that fine-grained
> given the size of the zones on large memory configurations.
> 

Makes sense

Thanks,
Balbir Singh.

  reply	other threads:[~2016-06-27 12:48 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-21 14:15 Mel Gorman
2016-06-21 14:15 ` [PATCH 01/27] mm, vmstat: Add infrastructure for per-node vmstats Mel Gorman
2016-06-21 14:15 ` [PATCH 02/27] mm, vmscan: Move lru_lock to the node Mel Gorman
2016-06-21 14:15 ` [PATCH 03/27] mm, vmscan: Move LRU lists to node Mel Gorman
2016-06-22 12:50   ` Vlastimil Babka
2016-06-21 14:15 ` [PATCH 04/27] mm, vmscan: Begin reclaiming pages on a per-node basis Mel Gorman
2016-06-22 14:04   ` Vlastimil Babka
2016-06-22 16:00     ` Vlastimil Babka
2016-06-23 11:07       ` Mel Gorman
2016-06-23 11:13         ` Michal Hocko
2016-06-23 10:58     ` Mel Gorman
2016-06-21 14:15 ` [PATCH 05/27] mm, vmscan: Have kswapd only scan based on the highest requested zone Mel Gorman
2016-06-21 14:15 ` [PATCH 06/27] mm, vmscan: Make kswapd reclaim in terms of nodes Mel Gorman
2016-06-21 14:15 ` [PATCH 07/27] mm, vmscan: Remove balance gap Mel Gorman
2016-06-21 14:15 ` [PATCH 08/27] mm, vmscan: Simplify the logic deciding whether kswapd sleeps Mel Gorman
2016-06-22 15:30   ` Vlastimil Babka
2016-06-21 14:15 ` [PATCH 09/27] mm, vmscan: By default have direct reclaim only shrink once per node Mel Gorman
2016-06-21 14:15 ` [PATCH 10/27] mm, vmscan: Remove duplicate logic clearing node congestion and dirty state Mel Gorman
2016-06-21 14:15 ` [PATCH 11/27] mm: vmscan: Do not reclaim from kswapd if there is any eligible zone Mel Gorman
2016-06-21 14:15 ` [PATCH 12/27] mm, vmscan: Make shrink_node decisions more node-centric Mel Gorman
2016-06-22 13:20   ` Michal Hocko
2016-06-22 15:42   ` Vlastimil Babka
2016-06-21 14:15 ` [PATCH 13/27] mm, memcg: Move memcg limit enforcement from zones to nodes Mel Gorman
2016-06-22 13:15   ` Michal Hocko
2016-06-21 14:15 ` [PATCH 14/27] mm, workingset: Make working set detection node-aware Mel Gorman
2016-06-21 14:15 ` [PATCH 15/27] mm, page_alloc: Consider dirtyable memory in terms of nodes Mel Gorman
2016-06-22 14:15   ` Michal Hocko
2016-06-22 14:27     ` Michal Hocko
2016-06-23 12:53       ` Mel Gorman
2016-06-23 13:13         ` Michal Hocko
2016-06-21 14:15 ` [PATCH 16/27] mm: Move page mapped accounting to the node Mel Gorman
2016-06-21 22:32   ` Andrew Morton
2016-06-23  8:35     ` Mel Gorman
2016-06-22 14:35   ` Michal Hocko
2016-06-21 14:15 ` [PATCH 17/27] mm: Rename NR_ANON_PAGES to NR_ANON_MAPPED Mel Gorman
2016-06-22 14:28   ` Michal Hocko
2016-06-21 14:15 ` [PATCH 18/27] mm: Move most file-based accounting to the node Mel Gorman
2016-06-22 14:38   ` Michal Hocko
2016-06-21 14:15 ` [PATCH 19/27] mm: Move vmscan writes and file write " Mel Gorman
2016-06-22 14:40   ` Michal Hocko
2016-06-23 13:57     ` Mel Gorman
2016-06-23 14:06       ` Vlastimil Babka
2016-06-23 16:03         ` Mel Gorman
2016-06-21 14:15 ` [PATCH 20/27] mm, vmscan: Update classzone_idx if buffer_heads_over_limit Mel Gorman
2016-06-22 14:49   ` Michal Hocko
2016-06-21 14:16 ` [PATCH 21/27] mm, vmscan: Only wakeup kswapd once per node for the requested classzone Mel Gorman
2016-06-22 16:08   ` Vlastimil Babka
2016-06-21 14:16 ` [PATCH 22/27] mm: Convert zone_reclaim to node_reclaim Mel Gorman
2016-06-21 14:16 ` [PATCH 23/27] mm, vmscan: Add classzone information to tracepoints Mel Gorman
2016-06-21 14:16 ` [PATCH 24/27] mm, page_alloc: Remove fair zone allocation policy Mel Gorman
2016-06-21 14:16 ` [PATCH 25/27] mm: page_alloc: Cache the last node whose dirty limit is reached Mel Gorman
2016-06-21 14:16 ` [PATCH 26/27] mm: vmstat: Replace __count_zone_vm_events with a zone id equivalent Mel Gorman
2016-06-21 14:16 ` [PATCH 27/27] mm: vmstat: Account per-zone stalls and pages skipped during reclaim Mel Gorman
2016-06-23 10:26 ` [PATCH 00/27] Move LRU page reclaim from zones to nodes v7 Mel Gorman
2016-06-23 11:27   ` Michal Hocko
2016-06-23 12:33     ` Mel Gorman
2016-06-23 12:44       ` Michal Hocko
2016-06-23 21:45   ` Andrew Morton
2016-06-24  6:35 ` Balbir Singh
2016-06-24  7:50   ` Mel Gorman
2016-06-27 12:48     ` Balbir Singh [this message]
  -- strict thread matches above, loose matches on Subject: below --
2016-06-21 11:43 Mel Gorman

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