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

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Date:   Thu, 22 Sep 2016 14:51:48 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     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 09/21/2016 07:13 PM, Michal Hocko wrote:
> On Tue 06-09-16 15:52:56, Vlastimil Babka wrote:
> [...]
>> @@ -3204,6 +3199,15 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
>>  	if (compaction_retries <= max_retries)
>>  		return true;
>>  
>> +	/*
>> +	 * Make sure there is at least one attempt at the highest priority
>> +	 * if we exhausted all retries at the lower priorities
>> +	 */
>> +check_priority:
>> +	if (*compact_priority > MIN_COMPACT_PRIORITY) {
>> +		(*compact_priority)--;
>> +		return true;
> 
> Don't we want to reset compaction_retries here? Otherwise we can consume
> all retries on the lower priorities.

Good point, patch-fix below.

> Other than that it looks good to me. With that you can add
> Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!
 
>> +	}
>>  	return false;
>>  }
>>  #else
> 

----8<----
>From 465e1bd61b7a6d6901a44f09b1a76514dbc220fa Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@...e.cz>
Date: Thu, 22 Sep 2016 13:54:32 +0200
Subject: [PATCH] mm, compaction: more reliably increase direct compaction
 priority-fix

When increasing the compaction priority, also reset retries. Otherwise we can
consume all retries on the lower priorities.

Suggested-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/page_alloc.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f8bed910e3cf..82fdb690ac62 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3162,7 +3162,7 @@ static inline bool
 should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
 		     enum compact_result compact_result,
 		     enum compact_priority *compact_priority,
-		     int compaction_retries)
+		     int *compaction_retries)
 {
 	int max_retries = MAX_COMPACT_RETRIES;
 
@@ -3196,16 +3196,17 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
 	 */
 	if (order > PAGE_ALLOC_COSTLY_ORDER)
 		max_retries /= 4;
-	if (compaction_retries <= max_retries)
+	if (*compaction_retries <= max_retries)
 		return true;
 
 	/*
-	 * Make sure there is at least one attempt at the highest priority
-	 * if we exhausted all retries at the lower priorities
+	 * Make sure there are attempts at the highest priority if we exhausted
+	 * all retries or failed at the lower priorities.
 	 */
 check_priority:
 	if (*compact_priority > MIN_COMPACT_PRIORITY) {
 		(*compact_priority)--;
+		*compaction_retries = 0;
 		return true;
 	}
 	return false;
@@ -3224,7 +3225,7 @@ static inline bool
 should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_flags,
 		     enum compact_result compact_result,
 		     enum compact_priority *compact_priority,
-		     int compaction_retries)
+		     int *compaction_retries)
 {
 	struct zone *zone;
 	struct zoneref *z;
@@ -3663,7 +3664,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	if (did_some_progress > 0 &&
 			should_compact_retry(ac, order, alloc_flags,
 				compact_result, &compact_priority,
-				compaction_retries))
+				&compaction_retries))
 		goto retry;
 
 	/* Reclaim has failed us, start killing things */
-- 
2.10.0