From: Vlastimil Babka <vbabka@suse.cz> To: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@techsingularity.net>, David Rientjes <rientjes@google.com>, kernel-team@fb.com, kernel-team@lge.com Subject: Re: [PATCH v3 2/8] mm, compaction: remove redundant watermark check in compact_finished() Date: Wed, 29 Mar 2017 17:30:58 +0200 [thread overview] Message-ID: <6af76744-260d-fc39-b6e0-fb47d7d6348b@suse.cz> (raw) In-Reply-To: <20170316013018.GA14063@js1304-P5Q-DELUXE> On 03/16/2017 02:30 AM, Joonsoo Kim wrote: > Hello, Hi, sorry for the late replies. > On Tue, Mar 07, 2017 at 02:15:39PM +0100, Vlastimil Babka wrote: >> When detecting whether compaction has succeeded in forming a high-order page, >> __compact_finished() employs a watermark check, followed by an own search for >> a suitable page in the freelists. This is not ideal for two reasons: >> >> - The watermark check also searches high-order freelists, but has a less strict >> criteria wrt fallback. It's therefore redundant and waste of cycles. This was >> different in the past when high-order watermark check attempted to apply >> reserves to high-order pages. > > Although it looks redundant now, I don't like removal of the watermark > check here. Criteria in watermark check would be changed to more strict > later and we would easily miss to apply it on compaction side if the > watermark check is removed. I see, but compaction is already full of various watermark(-like) checks that have to be considered/updated if watermark checking changes significantly, or things will go subtly wrong. I doubt this extra check can really help much in such cases. >> >> - The watermark check might actually fail due to lack of order-0 pages. >> Compaction can't help with that, so there's no point in continuing because of >> that. It's possible that high-order page still exists and it terminates. > > If lack of order-0 pages is the reason for stopping compaction, we > need to insert the watermark check for order-0 to break the compaction > instead of removing it. Am I missing something? You proposed that once IIRC, but didn't follow up? Currently we learn about insufficient order-0 watermark in __isolate_free_page() from the free scanner. We could potentially stop compacting earlier by checking it also in compact_finished(), but maybe it doesn't happen that often and it's just extra checking overhead. So I wouldn't be terribly opposed by converting the current check to an order-0 fail-compaction check (instead of removing it), but I really wouldn't like to insert the order-0 one and also keep the current one. > Thanks. >
WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz> To: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@techsingularity.net>, David Rientjes <rientjes@google.com>, kernel-team@fb.com, kernel-team@lge.com Subject: Re: [PATCH v3 2/8] mm, compaction: remove redundant watermark check in compact_finished() Date: Wed, 29 Mar 2017 17:30:58 +0200 [thread overview] Message-ID: <6af76744-260d-fc39-b6e0-fb47d7d6348b@suse.cz> (raw) In-Reply-To: <20170316013018.GA14063@js1304-P5Q-DELUXE> On 03/16/2017 02:30 AM, Joonsoo Kim wrote: > Hello, Hi, sorry for the late replies. > On Tue, Mar 07, 2017 at 02:15:39PM +0100, Vlastimil Babka wrote: >> When detecting whether compaction has succeeded in forming a high-order page, >> __compact_finished() employs a watermark check, followed by an own search for >> a suitable page in the freelists. This is not ideal for two reasons: >> >> - The watermark check also searches high-order freelists, but has a less strict >> criteria wrt fallback. It's therefore redundant and waste of cycles. This was >> different in the past when high-order watermark check attempted to apply >> reserves to high-order pages. > > Although it looks redundant now, I don't like removal of the watermark > check here. Criteria in watermark check would be changed to more strict > later and we would easily miss to apply it on compaction side if the > watermark check is removed. I see, but compaction is already full of various watermark(-like) checks that have to be considered/updated if watermark checking changes significantly, or things will go subtly wrong. I doubt this extra check can really help much in such cases. >> >> - The watermark check might actually fail due to lack of order-0 pages. >> Compaction can't help with that, so there's no point in continuing because of >> that. It's possible that high-order page still exists and it terminates. > > If lack of order-0 pages is the reason for stopping compaction, we > need to insert the watermark check for order-0 to break the compaction > instead of removing it. Am I missing something? You proposed that once IIRC, but didn't follow up? Currently we learn about insufficient order-0 watermark in __isolate_free_page() from the free scanner. We could potentially stop compacting earlier by checking it also in compact_finished(), but maybe it doesn't happen that often and it's just extra checking overhead. So I wouldn't be terribly opposed by converting the current check to an order-0 fail-compaction check (instead of removing it), but I really wouldn't like to insert the order-0 one and also keep the current one. > Thanks. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-03-29 15:31 UTC|newest] Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-07 13:15 [PATCH v3 0/8] try to reduce fragmenting fallbacks Vlastimil Babka 2017-03-07 13:15 ` Vlastimil Babka 2017-03-07 13:15 ` [PATCH v3 1/8] mm, compaction: reorder fields in struct compact_control Vlastimil Babka 2017-03-07 13:15 ` Vlastimil Babka 2017-03-07 13:15 ` [PATCH v3 2/8] mm, compaction: remove redundant watermark check in compact_finished() Vlastimil Babka 2017-03-07 13:15 ` Vlastimil Babka 2017-03-16 1:30 ` Joonsoo Kim 2017-03-16 1:30 ` Joonsoo Kim 2017-03-29 15:30 ` Vlastimil Babka [this message] 2017-03-29 15:30 ` Vlastimil Babka 2017-03-07 13:15 ` [PATCH v3 3/8] mm, page_alloc: split smallest stolen page in fallback Vlastimil Babka 2017-03-07 13:15 ` Vlastimil Babka 2017-03-07 13:15 ` [PATCH v3 4/8] mm, page_alloc: count movable pages when stealing from pageblock Vlastimil Babka 2017-03-07 13:15 ` Vlastimil Babka 2017-03-16 1:53 ` Joonsoo Kim 2017-03-16 1:53 ` Joonsoo Kim 2017-03-29 15:49 ` Vlastimil Babka 2017-03-29 15:49 ` Vlastimil Babka 2017-03-07 13:15 ` [PATCH v3 5/8] mm, compaction: change migrate_async_suitable() to suitable_migration_source() Vlastimil Babka 2017-03-07 13:15 ` Vlastimil Babka 2017-03-07 13:15 ` [PATCH v3 6/8] mm, compaction: add migratetype to compact_control Vlastimil Babka 2017-03-07 13:15 ` Vlastimil Babka 2017-03-07 13:15 ` [PATCH v3 7/8] mm, compaction: restrict async compaction to pageblocks of same migratetype Vlastimil Babka 2017-03-07 13:15 ` Vlastimil Babka 2017-03-16 2:14 ` Joonsoo Kim 2017-03-16 2:14 ` Joonsoo Kim 2017-03-29 16:06 ` Vlastimil Babka 2017-03-29 16:06 ` Vlastimil Babka 2017-04-07 0:38 ` Joonsoo Kim 2017-04-07 0:38 ` Joonsoo Kim 2017-05-04 6:12 ` Vlastimil Babka 2017-05-04 6:12 ` Vlastimil Babka 2017-03-07 13:15 ` [PATCH v3 8/8] mm, compaction: finish whole pageblock to reduce fragmentation Vlastimil Babka 2017-03-07 13:15 ` Vlastimil Babka 2017-03-16 2:18 ` Joonsoo Kim 2017-03-16 2:18 ` Joonsoo Kim 2017-03-29 16:13 ` Vlastimil Babka 2017-03-29 16:13 ` Vlastimil Babka 2017-03-08 16:46 ` [PATCH v3 0/8] try to reduce fragmenting fallbacks Johannes Weiner 2017-03-08 16:46 ` Johannes Weiner 2017-03-08 19:17 ` Vlastimil Babka 2017-03-08 19:17 ` Vlastimil Babka 2017-03-16 18:34 ` Johannes Weiner 2017-03-16 18:34 ` Johannes Weiner 2017-03-17 18:29 ` Vlastimil Babka 2017-03-17 18:29 ` Vlastimil Babka 2017-03-19 21:23 ` Johannes Weiner 2017-03-19 21:23 ` Johannes Weiner
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