From: Vlastimil Babka <vbabka@suse.cz>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Mel Gorman <mgorman@techsingularity.net>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
kernel-team@fb.com
Subject: Re: [RFC 4/4] mm, page_alloc: disallow migratetype fallback in fastpath
Date: Thu, 13 Oct 2016 13:46:05 +0200 [thread overview]
Message-ID: <1a4548bd-a9b3-e6c0-7b4f-e75b5e4f4cbd@suse.cz> (raw)
In-Reply-To: <20161013075856.GC2306@js1304-P5Q-DELUXE>
On 10/13/2016 09:58 AM, Joonsoo Kim wrote:
> On Thu, Sep 29, 2016 at 11:05:48PM +0200, Vlastimil Babka wrote:
>> The previous patch has adjusted async compaction so that it helps against
>> longterm fragmentation when compacting for a non-MOVABLE high-order allocation.
>> The goal of this patch is to force such allocations go through compaction
>> once before being allowed to fallback to a pageblock of different migratetype
>> (e.g. MOVABLE). In contexts where compaction is not allowed (and for order-0
>> allocations), this delayed fallback possibility can still help by trying a
>> different zone where fallback might not be needed and potentially waking up
>> kswapd earlier.
>
> Hmm... can we justify this compaction overhead in case of that there is
> high order freepages in other migratetype pageblock? There is no guarantee
> that longterm fragmentation happens and it affects the system
> peformance.
Yeah, I hoped testing would show whether this makes any difference, and
what the overhead is, and then we can decide whether it's worth.
> And, it would easilly fail to compact in unmovable pageblock since
> there would not be migratable pages if everything works as our
> intended. So, I guess that checking it over and over doesn't help to
> reduce fragmentation and just increase latency of allocation.
The pageblock isolation_suitable heuristics of compaction should
mitigate rescanning blocks without success. We could also add a per-zone
flag that gets set during a fallback allocation event and cleared by
finished compaction, or something.
> Thanks.
>
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next prev parent reply other threads:[~2016-10-13 11:46 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-28 1:41 Regression in mobility grouping? Johannes Weiner
2016-09-28 9:00 ` Vlastimil Babka
2016-09-28 15:39 ` Johannes Weiner
2016-09-29 2:25 ` Johannes Weiner
2016-09-29 6:14 ` Joonsoo Kim
2016-09-29 16:14 ` Johannes Weiner
2016-10-13 7:33 ` Joonsoo Kim
2016-09-29 7:17 ` Vlastimil Babka
2016-09-28 10:26 ` Mel Gorman
2016-09-28 16:37 ` Johannes Weiner
2016-09-29 21:05 ` [RFC 0/4] try to reduce fragmenting fallbacks Vlastimil Babka
2016-09-29 21:05 ` [RFC 1/4] mm, compaction: change migrate_async_suitable() to suitable_migration_source() Vlastimil Babka
2016-09-29 21:05 ` [RFC 2/4] mm, compaction: add migratetype to compact_control Vlastimil Babka
2016-09-29 21:05 ` [RFC 3/4] mm, compaction: restrict async compaction to matching migratetype Vlastimil Babka
2016-09-29 21:05 ` [RFC 4/4] mm, page_alloc: disallow migratetype fallback in fastpath Vlastimil Babka
2016-10-12 14:51 ` Vlastimil Babka
2016-10-13 7:58 ` Joonsoo Kim
2016-10-13 11:46 ` Vlastimil Babka [this message]
2016-10-07 8:32 ` [RFC 5/4] mm, page_alloc: split smallest stolen page in fallback Vlastimil Babka
2016-10-10 17:16 ` [RFC 0/4] try to reduce fragmenting fallbacks Johannes Weiner
2016-10-11 13:11 ` [RFC 6/4] mm, page_alloc: introduce MIGRATE_MIXED migratetype Vlastimil Babka
2016-10-13 14:11 ` [RFC 7/4] mm, page_alloc: count movable pages when stealing Vlastimil Babka
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