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From: Mike Kravetz <mike.kravetz@oracle.com>
To: Hillf Danton <hdanton@sina.com>, Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH RESEND 0/8] hugetlb: add demote/split page functionality
Date: Wed, 8 Sep 2021 14:00:19 -0700	[thread overview]
Message-ID: <6c42bed7-d4dd-e5eb-5a74-24cf64bf52d3@oracle.com> (raw)
In-Reply-To: <20210907085001.3773-1-hdanton@sina.com>

On 9/7/21 1:50 AM, Hillf Danton wrote:
> On Mon, 6 Sep 2021 16:40:28 +0200 Vlastimil Babka wrote:
>> On 9/2/21 20:17, Mike Kravetz wrote:
>>>
>>> Here is some very high level information from a long stall that was
>>> interrupted.  This was an order 9 allocation from alloc_buddy_huge_page().
>>>
>>> 55269.530564] __alloc_pages_slowpath: jiffies 47329325 tries 609673 cpu_tries 1   node 0 FAIL
>>> [55269.539893]     r_tries 25       c_tries 609647   reclaim 47325161 compact 607     
>>>
>>> Yes, in __alloc_pages_slowpath for 47329325 jiffies before being interrupted.
>>> should_reclaim_retry returned true 25 times and should_compact_retry returned
>>> true 609647 times.
>>> Almost all time (47325161 jiffies) spent in __alloc_pages_direct_reclaim, and
>>> 607 jiffies spent in __alloc_pages_direct_compact.
>>>
>>> Looks like both
>>> reclaim retries > MAX_RECLAIM_RETRIES
>>> and
>>> compaction retries > MAX_COMPACT_RETRIES
>>>
>> Yeah AFAICS that's only possible with the scenario I suspected. I guess
>> we should put a limit on compact retries (maybe some multiple of
>> MAX_COMPACT_RETRIES) even if it thinks that reclaim could help, while
>> clearly it doesn't (i.e. because somebody else is stealing the page like
>> in your test case).
> 
> And/or clamp reclaim retries for costly orders
> 
> 	reclaim retries = MAX_RECLAIM_RETRIES - order;
> 
> to pull down the chance for stall as low as possible.

Thanks, and sorry for not replying quickly.  I only get back to this as
time allows.

We could clamp the number of compaction and reclaim retries in
__alloc_pages_slowpath as suggested.  However, I noticed that a single
reclaim call could take a bunch of time.  As a result, I instrumented
shrink_node to see what might be happening.  Here is some information
from a long stall.  Note that I only dump stats when jiffies > 100000.

[ 8136.874706] shrink_node: 507654 total jiffies,  3557110 tries
[ 8136.881130]              130596341 reclaimed, 32 nr_to_reclaim
[ 8136.887643]              compaction_suitable results:
[ 8136.893276]     idx COMPACT_SKIPPED, 3557109
[ 8672.399839] shrink_node: 522076 total jiffies,  3466228 tries
[ 8672.406268]              124427720 reclaimed, 32 nr_to_reclaim
[ 8672.412782]              compaction_suitable results:
[ 8672.418421]     idx COMPACT_SKIPPED, 3466227
[ 8908.099592] __alloc_pages_slowpath: jiffies 2939938  tries 17068 cpu_tries 1   node 0 success
[ 8908.109120]     r_tries 11       c_tries 17056    reclaim 2939865  compact 9

In this case, clamping the number of retries from should_compact_retry
and should_reclaim_retry could help.  Mostly because we will not be
calling back into the reclaim code?  Notice the long amount of time spent
in shrink_node.  The 'tries' in shrink_node come about from that:

	if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
				    sc))
		goto again;

compaction_suitable results is the values returned from calls to
should_continue_reclaim -> compaction_suitable.

Trying to think if there might be an intelligent way to quit early.
-- 
Mike Kravetz

  parent reply	other threads:[~2021-09-08 21:00 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-16 22:49 Mike Kravetz
2021-08-16 22:49 ` [PATCH 1/8] hugetlb: add demote hugetlb page sysfs interfaces Mike Kravetz
2021-08-16 22:49 ` [PATCH 2/8] hugetlb: add HPageCma flag and code to free non-gigantic pages in CMA Mike Kravetz
2021-08-16 22:49 ` [PATCH 3/8] hugetlb: add demote bool to gigantic page routines Mike Kravetz
2021-08-16 22:49 ` [PATCH 4/8] hugetlb: add hugetlb demote page support Mike Kravetz
2021-08-16 22:49 ` [PATCH 5/8] hugetlb: document the demote sysfs interfaces Mike Kravetz
2021-08-16 23:28   ` Andrew Morton
2021-08-17  1:04     ` Mike Kravetz
2021-09-21 13:52   ` Aneesh Kumar K.V
2021-09-21 17:17     ` Mike Kravetz
2021-08-16 22:49 ` [PATCH 6/8] hugetlb: vmemmap optimizations when demoting hugetlb pages Mike Kravetz
2021-08-16 22:49 ` [PATCH 7/8] hugetlb: prepare destroy and prep routines for vmemmap optimized pages Mike Kravetz
2021-08-16 22:49 ` [PATCH 8/8] hugetlb: Optimized demote vmemmap optimizatized pages Mike Kravetz
2021-08-16 23:23 ` [PATCH RESEND 0/8] hugetlb: add demote/split page functionality Andrew Morton
2021-08-17  0:17   ` Mike Kravetz
2021-08-17  0:39     ` Andrew Morton
2021-08-17  0:58       ` Mike Kravetz
2021-08-16 23:27 ` Andrew Morton
2021-08-17  0:46   ` Mike Kravetz
2021-08-17  1:46     ` Andrew Morton
2021-08-17  7:30       ` David Hildenbrand
2021-08-17 16:19         ` Mike Kravetz
2021-08-17 18:49           ` David Hildenbrand
2021-08-24 22:08       ` Mike Kravetz
2021-08-27 17:22         ` Vlastimil Babka
2021-08-27 23:04           ` Mike Kravetz
2021-08-30 10:11             ` Vlastimil Babka
2021-09-02 18:17               ` Mike Kravetz
2021-09-06 14:40                 ` Vlastimil Babka
     [not found]                 ` <20210907085001.3773-1-hdanton@sina.com>
2021-09-08 21:00                   ` Mike Kravetz [this message]
2021-09-09 11:54                     ` Michal Hocko
2021-09-09 13:45                       ` Vlastimil Babka
2021-09-09 21:31                         ` Mike Kravetz
2021-09-10  8:20                         ` Michal Hocko
2021-09-11  0:11                           ` Mike Kravetz
2021-09-13 15:50                             ` Michal Hocko
2021-09-15 16:57                               ` Mike Kravetz
2021-09-17 20:44                                 ` Mike Kravetz

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