linux-kernel - Re: [PATCH 1/3] mm, reclaim: make should_continue

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Date:   Mon, 5 Aug 2019 09:54:45 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Hillf Danton <hdanton@...a.com>, Michal Hocko <mhocko@...nel.org>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/3] mm, reclaim: make should_continue_reclaim perform
 dryrun detection

On 8/5/19 1:42 AM, Vlastimil Babka wrote:
> On 8/3/19 12:39 AM, Mike Kravetz wrote:
>> From: Hillf Danton <hdanton@...a.com>
>>
>> Address the issue of should_continue_reclaim continuing true too often
>> for __GFP_RETRY_MAYFAIL attempts when !nr_reclaimed and nr_scanned.
>> This could happen during hugetlb page allocation causing stalls for
>> minutes or hours.
>>
>> We can stop reclaiming pages if compaction reports it can make a progress.
>> A code reshuffle is needed to do that.
> 
>> And it has side-effects, however,
>> with allocation latencies in other cases but that would come at the cost
>> of potential premature reclaim which has consequences of itself.
> 
> Based on Mel's longer explanation, can we clarify the wording here? e.g.:
> 
> There might be side-effect for other high-order allocations that would
> potentially benefit from more reclaim before compaction for them to be
> faster and less likely to stall, but the consequences of
> premature/over-reclaim are considered worse.
> 
>> We can also bail out of reclaiming pages if we know that there are not
>> enough inactive lru pages left to satisfy the costly allocation.
>>
>> We can give up reclaiming pages too if we see dryrun occur, with the
>> certainty of plenty of inactive pages. IOW with dryrun detected, we are
>> sure we have reclaimed as many pages as we could.
>>
>> Cc: Mike Kravetz <mike.kravetz@...cle.com>
>> Cc: Mel Gorman <mgorman@...e.de>
>> Cc: Michal Hocko <mhocko@...nel.org>
>> Cc: Vlastimil Babka <vbabka@...e.cz>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Signed-off-by: Hillf Danton <hdanton@...a.com>
>> Tested-by: Mike Kravetz <mike.kravetz@...cle.com>
>> Acked-by: Mel Gorman <mgorman@...e.de>
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> I will send some followup cleanup.
> 
> There should be also Mike's SOB?

Will do.
My apologies, the process of handling patches created by others is new
to me.

Also, will incorporate Mel's explanation.
-- 
Mike Kravetz