From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
David Rientjes <rientjes@google.com>,
Rik van Riel <riel@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 08/11] mm, compaction: create compact_gap wrapper
Date: Tue, 16 Aug 2016 15:41:04 +0900 [thread overview]
Message-ID: <20160816064104.GG17448@js1304-P5Q-DELUXE> (raw)
In-Reply-To: <656fea7f-753d-df56-744a-50b90f9a3842@suse.cz>
On Tue, Aug 16, 2016 at 08:15:36AM +0200, Vlastimil Babka wrote:
> On 08/16/2016 08:15 AM, Joonsoo Kim wrote:
> >On Wed, Aug 10, 2016 at 11:12:23AM +0200, Vlastimil Babka wrote:
> >>--- a/include/linux/compaction.h
> >>+++ b/include/linux/compaction.h
> >>@@ -58,6 +58,22 @@ enum compact_result {
> >>
> >> struct alloc_context; /* in mm/internal.h */
> >>
> >>+/*
> >>+ * Number of free order-0 pages that should be available above given watermark
> >>+ * to make sure compaction has reasonable chance of not running out of free
> >>+ * pages that it needs to isolate as migration target during its work.
> >>+ */
> >>+static inline unsigned long compact_gap(unsigned int order)
> >>+{
> >>+ /*
> >>+ * Although all the isolations for migration are temporary, compaction
> >>+ * may have up to 1 << order pages on its list and then try to split
> >>+ * an (order - 1) free page. At that point, a gap of 1 << order might
> >>+ * not be enough, so it's safer to require twice that amount.
> >>+ */
> >>+ return 2UL << order;
> >>+}
> >
> >I agree with this wrapper function but there is a question.
> >
> >Could you elaborate more on this code comment? Freescanner could keep
> >COMPACT_CLUSTER_MAX freepages on the list. It's not associated with
> >requested order at least for now. Why compact_gap is 2UL << order in
> >this case?
>
> It's true that for high enough order, COMPACT_CLUSTER_MAX might be
> more limiting than 1 << order. But then it also helps to have more
AFAIK, regardless of order, migration scanner isolates
COMPACT_CLUSTER_MAX pages. And, freepage scanner isolates
more than nr_migratepages freepages.
> free pages for probability of compaction success, so I don't think
> it's worth complicating the compact_gap() formula.
I agree that it's not worth complicating the compact_gap() formula but
it would be better to fix the comment?
Thanks.
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next prev parent reply other threads:[~2016-08-16 6:35 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-10 9:12 [PATCH v6 00/11] make direct compaction more deterministic Vlastimil Babka
2016-08-10 9:12 ` [PATCH v6 01/11] mm, compaction: make whole_zone flag ignore cached scanner positions Vlastimil Babka
2016-08-10 9:12 ` [PATCH v6 02/11] mm, compaction: cleanup unused functions Vlastimil Babka
2016-08-10 9:12 ` [PATCH v6 03/11] mm, compaction: rename COMPACT_PARTIAL to COMPACT_SUCCESS Vlastimil Babka
2016-08-18 9:01 ` Michal Hocko
2016-08-10 9:12 ` [PATCH v6 04/11] mm, compaction: don't recheck watermarks after COMPACT_SUCCESS Vlastimil Babka
2016-08-16 6:12 ` Joonsoo Kim
2016-08-16 6:11 ` Vlastimil Babka
2016-08-18 11:59 ` Vlastimil Babka
2016-08-18 9:03 ` Michal Hocko
2016-08-10 9:12 ` [PATCH v6 05/11] mm, compaction: add the ultimate direct compaction priority Vlastimil Babka
2016-08-16 5:58 ` Joonsoo Kim
2016-08-18 12:23 ` Vlastimil Babka
2016-08-10 9:12 ` [PATCH v6 06/11] mm, compaction: more reliably increase " Vlastimil Babka
2016-08-16 6:07 ` Joonsoo Kim
2016-08-16 6:31 ` Vlastimil Babka
2016-08-18 9:10 ` Michal Hocko
2016-08-18 9:44 ` Vlastimil Babka
2016-08-18 9:48 ` Michal Hocko
2016-08-10 9:12 ` [PATCH v6 07/11] mm, compaction: use correct watermark when checking compaction success Vlastimil Babka
2016-08-10 9:12 ` [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Vlastimil Babka
2016-08-16 6:15 ` Joonsoo Kim
2016-08-16 6:15 ` Vlastimil Babka
2016-08-16 6:41 ` Joonsoo Kim [this message]
2016-08-18 12:13 ` Vlastimil Babka
2016-08-10 9:12 ` [PATCH v6 09/11] mm, compaction: use proper alloc_flags in __compaction_suitable() Vlastimil Babka
2016-08-10 9:12 ` [PATCH v6 10/11] mm, compaction: require only min watermarks for non-costly orders Vlastimil Babka
2016-08-16 6:16 ` Joonsoo Kim
2016-08-16 6:36 ` Vlastimil Babka
2016-08-16 6:46 ` Joonsoo Kim
2016-08-18 12:20 ` Vlastimil Babka
2016-08-10 9:12 ` [PATCH v6 11/11] mm, vmscan: make compaction_ready() more accurate and readable Vlastimil Babka
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