linux-kernel - Re: [PATCH 2/4] mm, compaction: more reliably increase direct compaction priority

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Date:   Fri, 23 Sep 2016 12:47:23 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Hillf Danton <hillf.zj@...baba-inc.com>,
        'Andrew Morton' <akpm@...ux-foundation.org>,
        'Arkadiusz Miskiewicz' <a.miskiewicz@...il.com>,
        'Ralf-Peter Rohbeck' <Ralf-Peter.Rohbeck@...ntum.com>,
        'Olaf Hering' <olaf@...fle.de>, linux-kernel@...r.kernel.org,
        'Linus Torvalds' <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, 'Mel Gorman' <mgorman@...hsingularity.net>,
        'Joonsoo Kim' <iamjoonsoo.kim@....com>,
        'David Rientjes' <rientjes@...gle.com>,
        'Rik van Riel' <riel@...hat.com>
Subject: Re: [PATCH 2/4] mm, compaction: more reliably increase direct
 compaction priority

On 09/23/2016 10:23 AM, Michal Hocko wrote:
> On Fri 23-09-16 08:55:33, Vlastimil Babka wrote:
> [...]
>> >From 1623d5bd441160569ffad3808aeeec852048e558 Mon Sep 17 00:00:00 2001
>> From: Vlastimil Babka <vbabka@...e.cz>
>> Date: Thu, 22 Sep 2016 17:02:37 +0200
>> Subject: [PATCH] mm, page_alloc: pull no_progress_loops update to
>>  should_reclaim_retry()
>>
>> The should_reclaim_retry() makes decisions based on no_progress_loops, so it
>> makes sense to also update the counter there. It will be also consistent with
>> should_compact_retry() and compaction_retries. No functional change.
>>
>> [hillf.zj@...baba-inc.com: fix missing pointer dereferences]
>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
>> Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>
> 
> OK, this looks reasonable to me. Could you post both patches in a

Both? I would argue that [1] might be relevant because it resets the
number of retries. Only the should_reclaim_retry() cleanup is not
stricly needed.

[1] http://lkml.kernel.org/r/<deec7319-2976-6d34-ab7b-afbb3f6c32f8@...e.cz>

> separate thread please? They shouldn't be really needed to mitigate the
> pre-mature oom killer issues. Feel free to add
> Acked-by: Michal Hocko <mhocko@...e.com>
> 
> Thanks!
> 
>> ---
>>  mm/page_alloc.c | 28 ++++++++++++++--------------
>>  1 file changed, 14 insertions(+), 14 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 582820080601..6039ff40452c 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -3401,16 +3401,26 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
>>  static inline bool
>>  should_reclaim_retry(gfp_t gfp_mask, unsigned order,
>>  		     struct alloc_context *ac, int alloc_flags,
>> -		     bool did_some_progress, int no_progress_loops)
>> +		     bool did_some_progress, int *no_progress_loops)
>>  {
>>  	struct zone *zone;
>>  	struct zoneref *z;
>>  
>>  	/*
>> +	 * Costly allocations might have made a progress but this doesn't mean
>> +	 * their order will become available due to high fragmentation so
>> +	 * always increment the no progress counter for them
>> +	 */
>> +	if (did_some_progress && order <= PAGE_ALLOC_COSTLY_ORDER)
>> +		*no_progress_loops = 0;
>> +	else
>> +		(*no_progress_loops)++;
>> +
>> +	/*
>>  	 * Make sure we converge to OOM if we cannot make any progress
>>  	 * several times in the row.
>>  	 */
>> -	if (no_progress_loops > MAX_RECLAIM_RETRIES)
>> +	if (*no_progress_loops > MAX_RECLAIM_RETRIES)
>>  		return false;
>>  
>>  	/*
>> @@ -3425,7 +3435,7 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
>>  		unsigned long reclaimable;
>>  
>>  		available = reclaimable = zone_reclaimable_pages(zone);
>> -		available -= DIV_ROUND_UP(no_progress_loops * available,
>> +		available -= DIV_ROUND_UP((*no_progress_loops) * available,
>>  					  MAX_RECLAIM_RETRIES);
>>  		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
>>  
>> @@ -3641,18 +3651,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  	if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_REPEAT))
>>  		goto nopage;
>>  
>> -	/*
>> -	 * Costly allocations might have made a progress but this doesn't mean
>> -	 * their order will become available due to high fragmentation so
>> -	 * always increment the no progress counter for them
>> -	 */
>> -	if (did_some_progress && order <= PAGE_ALLOC_COSTLY_ORDER)
>> -		no_progress_loops = 0;
>> -	else
>> -		no_progress_loops++;
>> -
>>  	if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags,
>> -				 did_some_progress > 0, no_progress_loops))
>> +				 did_some_progress > 0, &no_progress_loops))
>>  		goto retry;
>>  
>>  	/*
>> -- 
>> 2.10.0
>>
>>
>> --
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