From: Vlastimil Babka <vbabka@suse.cz>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Mel Gorman <mgorman@techsingularity.net>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linux-MM <linux-mm@kvack.org>, Rik van Riel <riel@surriel.com>,
Johannes Weiner <hannes@cmpxchg.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 08/31] mm, vmscan: simplify the logic deciding whether kswapd sleeps
Date: Thu, 14 Jul 2016 10:32:09 +0200 [thread overview]
Message-ID: <5b6b1490-1dbc-74fc-e129-947141a1bee3@suse.cz> (raw)
In-Reply-To: <20160714052332.GA29676@js1304-P5Q-DELUXE>
On 07/14/2016 07:23 AM, Joonsoo Kim wrote:
> On Fri, Jul 08, 2016 at 11:11:47AM +0100, Mel Gorman wrote:
>> On Fri, Jul 08, 2016 at 11:44:47AM +0900, Joonsoo Kim wrote:
>>
>> It doesn't stop reclaiming for the lower zones. It's reclaiming the LRU
>> for the whole node that may or may not have lower zone pages at the end
>> of the LRU. If it does, then the allocation request will be satisfied.
>> If it does not, then kswapd will think the node is balanced and get
>> rewoken to do a zone-constrained reclaim pass.
>
> If zone-constrained request could go direct reclaim pass, there would
> be no problem. But, please assume that request is zone-constrained
> without __GFP_DIRECT_RECLAIM which is common for some device driver
> implementation. And, please assume one more thing that this request
> always comes with zone-unconstrained allocation request. In this case,
> your max() logic will set kswapd_classzone_idx to highest zone index
> and re-worken kswapd would not balance for low zone again. In the end,
> zone-constrained allocation request without __GFP_DIRECT_RECLAIM could
> fail.
I don't think there's a problem in the scenario? Kswapd will keep being
woken up and reclaim from the node lru. It will hit and free any low
zone pages that are on the lru, even though it doesn't "balance for low
zone". Eventually it will either satisfy the constrained allocation by
reclaiming those low-zone pages during the repeated wakeups, or the
low-zone wakeups will stop coming together with higher-zone wakeups and
then it will reclaim the low-zone pages in a single low-zone wakeup. If
the zone-constrained request is not allowed to fail, then it will just
keep waking up kswapd and waiting for the progress. If it's allowed to
fail (i.e. not __GFP_NOFAIL), but not allowed to direct reclaim, it goes
"goto nopage" rather quickly in __alloc_pages_slowpath(), without any
waiting for kswapd's progress, so there's not really much difference
whether the kswapd wakeup picked up a low classzone or not. Note the
__GFP_NOFAIL but ~__GFP_DIRECT_RECLAIM is a WARN_ON_ONCE() scenario, so
definitely not common...
> Thanks.
>
WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Mel Gorman <mgorman@techsingularity.net>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linux-MM <linux-mm@kvack.org>, Rik van Riel <riel@surriel.com>,
Johannes Weiner <hannes@cmpxchg.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 08/31] mm, vmscan: simplify the logic deciding whether kswapd sleeps
Date: Thu, 14 Jul 2016 10:32:09 +0200 [thread overview]
Message-ID: <5b6b1490-1dbc-74fc-e129-947141a1bee3@suse.cz> (raw)
In-Reply-To: <20160714052332.GA29676@js1304-P5Q-DELUXE>
On 07/14/2016 07:23 AM, Joonsoo Kim wrote:
> On Fri, Jul 08, 2016 at 11:11:47AM +0100, Mel Gorman wrote:
>> On Fri, Jul 08, 2016 at 11:44:47AM +0900, Joonsoo Kim wrote:
>>
>> It doesn't stop reclaiming for the lower zones. It's reclaiming the LRU
>> for the whole node that may or may not have lower zone pages at the end
>> of the LRU. If it does, then the allocation request will be satisfied.
>> If it does not, then kswapd will think the node is balanced and get
>> rewoken to do a zone-constrained reclaim pass.
>
> If zone-constrained request could go direct reclaim pass, there would
> be no problem. But, please assume that request is zone-constrained
> without __GFP_DIRECT_RECLAIM which is common for some device driver
> implementation. And, please assume one more thing that this request
> always comes with zone-unconstrained allocation request. In this case,
> your max() logic will set kswapd_classzone_idx to highest zone index
> and re-worken kswapd would not balance for low zone again. In the end,
> zone-constrained allocation request without __GFP_DIRECT_RECLAIM could
> fail.
I don't think there's a problem in the scenario? Kswapd will keep being
woken up and reclaim from the node lru. It will hit and free any low
zone pages that are on the lru, even though it doesn't "balance for low
zone". Eventually it will either satisfy the constrained allocation by
reclaiming those low-zone pages during the repeated wakeups, or the
low-zone wakeups will stop coming together with higher-zone wakeups and
then it will reclaim the low-zone pages in a single low-zone wakeup. If
the zone-constrained request is not allowed to fail, then it will just
keep waking up kswapd and waiting for the progress. If it's allowed to
fail (i.e. not __GFP_NOFAIL), but not allowed to direct reclaim, it goes
"goto nopage" rather quickly in __alloc_pages_slowpath(), without any
waiting for kswapd's progress, so there's not really much difference
whether the kswapd wakeup picked up a low classzone or not. Note the
__GFP_NOFAIL but ~__GFP_DIRECT_RECLAIM is a WARN_ON_ONCE() scenario, so
definitely not common...
> Thanks.
>
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next prev parent reply other threads:[~2016-07-14 8:32 UTC|newest]
Thread overview: 181+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-01 20:01 [PATCH 00/31] Move LRU page reclaim from zones to nodes v8 Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 01/31] mm, vmstat: add infrastructure for per-node vmstats Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-04 23:50 ` Minchan Kim
2016-07-04 23:50 ` Minchan Kim
2016-07-05 8:14 ` Mel Gorman
2016-07-05 8:14 ` Mel Gorman
2016-07-06 0:15 ` Minchan Kim
2016-07-06 0:15 ` Minchan Kim
2016-07-01 20:01 ` [PATCH 02/31] mm, vmscan: move lru_lock to the node Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-05 0:03 ` Minchan Kim
2016-07-05 0:03 ` Minchan Kim
2016-07-01 20:01 ` [PATCH 03/31] mm, vmscan: move LRU lists to node Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-05 1:19 ` Minchan Kim
2016-07-05 1:19 ` Minchan Kim
2016-07-05 10:14 ` Mel Gorman
2016-07-05 10:14 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-07 1:12 ` Joonsoo Kim
2016-07-07 1:12 ` Joonsoo Kim
2016-07-07 9:48 ` Mel Gorman
2016-07-07 9:48 ` Mel Gorman
2016-07-08 2:28 ` Joonsoo Kim
2016-07-08 2:28 ` Joonsoo Kim
2016-07-08 10:05 ` Mel Gorman
2016-07-08 10:05 ` Mel Gorman
2016-07-14 6:28 ` Joonsoo Kim
2016-07-14 6:28 ` Joonsoo Kim
2016-07-14 7:48 ` Vlastimil Babka
2016-07-14 7:48 ` Vlastimil Babka
2016-07-18 4:52 ` Joonsoo Kim
2016-07-18 4:52 ` Joonsoo Kim
2016-07-18 12:11 ` Mel Gorman
2016-07-18 12:11 ` Mel Gorman
2016-07-18 14:27 ` Mel Gorman
2016-07-18 14:27 ` Mel Gorman
2016-07-19 8:30 ` Joonsoo Kim
2016-07-19 8:30 ` Joonsoo Kim
2016-07-19 14:25 ` Mel Gorman
2016-07-19 14:25 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 05/31] mm, vmscan: have kswapd only scan based on the highest requested zone Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 06/31] mm, vmscan: make kswapd reclaim in terms of nodes Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 07/31] mm, vmscan: remove balance gap Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 08/31] mm, vmscan: simplify the logic deciding whether kswapd sleeps Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-05 5:59 ` Minchan Kim
2016-07-05 5:59 ` Minchan Kim
2016-07-05 10:26 ` Mel Gorman
2016-07-05 10:26 ` Mel Gorman
2016-07-06 0:30 ` Minchan Kim
2016-07-06 0:30 ` Minchan Kim
2016-07-06 8:31 ` Mel Gorman
2016-07-06 8:31 ` Mel Gorman
2016-07-07 5:51 ` Minchan Kim
2016-07-07 5:51 ` Minchan Kim
2016-07-07 9:56 ` Mel Gorman
2016-07-07 9:56 ` Mel Gorman
2016-07-07 1:20 ` Joonsoo Kim
2016-07-07 1:20 ` Joonsoo Kim
2016-07-07 10:17 ` Mel Gorman
2016-07-07 10:17 ` Mel Gorman
2016-07-08 2:44 ` Joonsoo Kim
2016-07-08 2:44 ` Joonsoo Kim
2016-07-08 10:11 ` Mel Gorman
2016-07-08 10:11 ` Mel Gorman
2016-07-14 5:23 ` Joonsoo Kim
2016-07-14 5:23 ` Joonsoo Kim
2016-07-14 8:32 ` Vlastimil Babka [this message]
2016-07-14 8:32 ` Vlastimil Babka
2016-07-18 5:07 ` Joonsoo Kim
2016-07-18 5:07 ` Joonsoo Kim
2016-07-18 6:51 ` Vlastimil Babka
2016-07-18 6:51 ` Vlastimil Babka
2016-07-18 7:24 ` Joonsoo Kim
2016-07-18 7:24 ` Joonsoo Kim
2016-07-14 9:05 ` Mel Gorman
2016-07-14 9:05 ` Mel Gorman
2016-07-18 5:03 ` Joonsoo Kim
2016-07-18 5:03 ` Joonsoo Kim
2016-07-01 20:01 ` [PATCH 09/31] mm, vmscan: by default have direct reclaim only shrink once per node Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-07 1:43 ` Joonsoo Kim
2016-07-07 1:43 ` Joonsoo Kim
2016-07-07 10:27 ` Mel Gorman
2016-07-07 10:27 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 10/31] mm, vmscan: remove duplicate logic clearing node congestion and dirty state Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 11/31] mm: vmscan: do not reclaim from kswapd if there is any eligible zone Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-05 6:11 ` Minchan Kim
2016-07-05 6:11 ` Minchan Kim
2016-07-05 10:38 ` Mel Gorman
2016-07-05 10:38 ` Mel Gorman
2016-07-06 1:25 ` Minchan Kim
2016-07-06 1:25 ` Minchan Kim
2016-07-06 8:42 ` Mel Gorman
2016-07-06 8:42 ` Mel Gorman
2016-07-07 6:27 ` Minchan Kim
2016-07-07 6:27 ` Minchan Kim
2016-07-07 10:55 ` Mel Gorman
2016-07-07 10:55 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 12/31] mm, vmscan: make shrink_node decisions more node-centric Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-05 6:24 ` Minchan Kim
2016-07-05 6:24 ` Minchan Kim
2016-07-05 10:40 ` Mel Gorman
2016-07-05 10:40 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 13/31] mm, memcg: move memcg limit enforcement from zones to nodes Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 14/31] mm, workingset: make working set detection node-aware Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 15/31] mm, page_alloc: consider dirtyable memory in terms of nodes Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 16/31] mm: move page mapped accounting to the node Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 17/31] mm: rename NR_ANON_PAGES to NR_ANON_MAPPED Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 18/31] mm: move most file-based accounting to the node Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 19/31] mm: move vmscan writes and file write " Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 20/31] mm, vmscan: only wakeup kswapd once per node for the requested classzone Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-07 1:24 ` Joonsoo Kim
2016-07-07 1:24 ` Joonsoo Kim
2016-07-07 10:58 ` Mel Gorman
2016-07-07 10:58 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 21/31] mm, page_alloc: Wake kswapd based on the highest eligible zone Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 22/31] mm: convert zone_reclaim to node_reclaim Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 23/31] mm, vmscan: Avoid passing in classzone_idx unnecessarily to shrink_node Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 24/31] mm, vmscan: Avoid passing in classzone_idx unnecessarily to compaction_ready Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 25/31] mm, vmscan: add classzone information to tracepoints Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 26/31] mm, page_alloc: remove fair zone allocation policy Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 27/31] mm: page_alloc: cache the last node whose dirty limit is reached Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 28/31] mm: vmstat: replace __count_zone_vm_events with a zone id equivalent Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 29/31] mm: vmstat: account per-zone stalls and pages skipped during reclaim Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 30/31] mm, vmstat: print node-based stats in zoneinfo file Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-01 20:01 ` [PATCH 31/31] mm, vmstat: Remove zone and node double accounting by approximating retries Mel Gorman
2016-07-01 20:01 ` Mel Gorman
2016-07-06 0:02 ` Minchan Kim
2016-07-06 0:02 ` Minchan Kim
2016-07-06 8:58 ` Mel Gorman
2016-07-06 8:58 ` Mel Gorman
2016-07-06 9:33 ` Mel Gorman
2016-07-06 9:33 ` Mel Gorman
2016-07-07 6:47 ` Minchan Kim
2016-07-07 6:47 ` Minchan Kim
2016-07-06 18:12 ` Dave Hansen
2016-07-06 18:12 ` Dave Hansen
2016-07-07 11:26 ` Mel Gorman
2016-07-07 11:26 ` Mel Gorman
2016-07-04 1:37 ` [PATCH 00/31] Move LRU page reclaim from zones to nodes v8 Minchan Kim
2016-07-04 1:37 ` Minchan Kim
2016-07-04 4:34 ` Mel Gorman
2016-07-04 4:34 ` Mel Gorman
2016-07-04 8:04 ` Minchan Kim
2016-07-04 8:04 ` Minchan Kim
2016-07-04 8:04 ` Minchan Kim
2016-07-04 9:55 ` Mel Gorman
2016-07-04 9:55 ` Mel Gorman
2016-07-06 1:51 ` Minchan Kim
2016-07-06 1:51 ` Minchan Kim
-- strict thread matches above, loose matches on Subject: below --
2016-07-01 15:37 Mel Gorman
2016-07-01 15:37 ` [PATCH 08/31] mm, vmscan: simplify the logic deciding whether kswapd sleeps Mel Gorman
2016-07-01 15:37 ` Mel Gorman
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