linux-kernel - Re: [PATCH v3 5/7] mm/compaction: respect compaction order when updating defer counter

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Date:	Mon, 7 Dec 2015 17:04:07 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan@...nel.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v3 5/7] mm/compaction: respect compaction order when
 updating defer counter

On Fri, Dec 04, 2015 at 06:15:02PM +0100, Vlastimil Babka wrote:
> On 12/03/2015 08:11 AM, Joonsoo Kim wrote:
> >It doesn't make sense that we reset defer counter
> >in compaction_defer_reset() when compaction request under the order of
> >compact_order_failed succeed. Fix it.
> 
> Right.
> 
> >And, it does make sense that giving enough chance for updated failed
> >order compaction before deferring. Change it.
> 
> Sorry, can't understand the meaning here. From the code it seems
> that you want to reset defer_shift to 0 instead of increasing it,
> when the current order is lower than the failed one? That makes
> sense, yeah.

You correctly understand my intention. :)

> How about this?
> 
> "On the other hand, when deferring compaction for an order lower
> than the current compact_order_failed, we can assume the lower order
> will recover more quickly, so we should reset the progress made
> previously on compact_defer_shift with the higher order."

Will add it.

> 
> >Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Thanks.
> 
> >---
> >  mm/compaction.c | 19 +++++++++++--------
> >  1 file changed, 11 insertions(+), 8 deletions(-)
> >
> >diff --git a/mm/compaction.c b/mm/compaction.c
> >index 67b8d90..1a75a6e 100644
> >--- a/mm/compaction.c
> >+++ b/mm/compaction.c
> >@@ -126,11 +126,14 @@ static struct page *pageblock_pfn_to_page(unsigned long start_pfn,
> >   */
> >  static void defer_compaction(struct zone *zone, int order)
> >  {
> >-	zone->compact_considered = 0;
> >-	zone->compact_defer_shift++;
> >-
> >-	if (order < zone->compact_order_failed)
> >+	if (order < zone->compact_order_failed) {
> >+		zone->compact_considered = 0;
> >+		zone->compact_defer_shift = 0;
> >  		zone->compact_order_failed = order;
> >+	} else {
> >+		zone->compact_considered = 0;
> >+		zone->compact_defer_shift++;
> >+	}
> >
> >  	if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
> >  		zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
> >@@ -161,11 +164,11 @@ bool compaction_deferred(struct zone *zone, int order)
> >  /* Update defer tracking counters after successful compaction of given order */
> >  static void compaction_defer_reset(struct zone *zone, int order)
> >  {
> >-	zone->compact_considered = 0;
> >-	zone->compact_defer_shift = 0;
> >-
> >-	if (order >= zone->compact_order_failed)
> >+	if (order >= zone->compact_order_failed) {
> >+		zone->compact_considered = 0;
> >+		zone->compact_defer_shift = 0;
> >  		zone->compact_order_failed = order + 1;
> >+	}
> >
> >  	trace_mm_compaction_defer_reset(zone, order);
> >  }
> >
> 
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