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From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	linux-mm@kvack.org, Michael Ellerman <mpe@ellerman.id.au>,
	Andrew Morton <akpm@linux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Reza Arbab <arbab@linux.vnet.ibm.com>,
	Yasuaki Ishimatsu <yasu.isimatu@gmail.com>,
	qiuxishi@huawei.com, Igor Mammedov <imammedo@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages
Date: Tue, 24 Oct 2017 14:25:26 +0200
Message-ID: <20171024122526.3kmabkcbmj4johli@dhcp22.suse.cz> (raw)
In-Reply-To: <fdb6b325-8de8-b809-81eb-c164736d6a58@suse.cz>

On Tue 24-10-17 10:12:58, Vlastimil Babka wrote:
> On 10/24/2017 06:44 AM, Joonsoo Kim wrote:
> >>> I'm not sure what is the confusing semantic you mentioned. I think
> >>> that set_migratetype_isolate() has confusing semantic and should be
> >>> fixed since making the pageblock isolated doesn't need to check if
> >>> there is unmovable page or not. Do you think that
> >>> set_migratetype_isolate() need to check it? If so, why?
> >>
> >> My intuitive understanding of set_migratetype_isolate is that it either
> >> suceeds and that means that the given pfn range can be isolated for the
> >> given type of allocation (be it movable or cma). No new pages will be
> >> allocated from this range to allow converging into a free range in a
> >> finit amount of time. At least this is how the hotplug code would like
> >> to use it and I suppose that the alloc_contig_range would like to
> >> guarantee the same to not rely on a fixed amount of migration attempts.
> > 
> > Yes, alloc_contig_range() also want to guarantee the similar thing.
> > Major difference between them is 'given pfn range'. memory hotplug
> > works by pageblock unit but alloc_contig_range() doesn't.
> > alloc_contig_range() works by the page unit. However, there is no easy
> > way to isolate individual page so it uses pageblock isolation
> > regardless of 'given pfn range'. In this case, checking movability of
> > all pages on the pageblock would cause the problem as I mentioned
> > before.
> 
> I couldn't look too closely yet, but do I understand correctly that the
> *potential* problem (because as you say there are no such
> alloc_contig_range callers) you are describing is not newly introduced
> by Michal's series? Then his patch fixing the introduced regression
> should be enough for now, and further improvements could be posted on
> top, and not vice versa? Please don't take it wrong, I agree the current
> state is a bit of a mess and improvements are welcome. Also it seems to
> me that Michal is right, and there's nothing preventing
> alloc_contig_range() to allocate from CMA pageblocks for non-CMA
> purposes (likely not movable), and that should be also fixed?

OK, it seems I understand Joonsoo's concern more now. And I agree with
Vlastimil, that it is better to plug the immediate regression with a
minimal patch and discuss general improvements of the pfn based
allocator separatelly. There are more things to clear up there,
including the proper API (alloc_contig_range is just too low level for
anybody to use) as well as the MIGRATE_* flags usage (e.g. I am not
really sure GB pages usage of MIGRATE_MOVABLE is really correct).
alloc_contig_range looks like an internal CMA function which has been
(ab)used for a different purpose to me rather than a well thought
through interface. MAP_CONTIG discussion has shown some interest in
an API for large allocations so I _believe_ we should think that through
befire we grow more unexpected users.

I am definitely willing to help there.

Is that something you would agree with Joonsoo?
-- 
Michal Hocko
SUSE Labs

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  reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-18  7:08 [PATCH v2 0/2] mm, memory_hotplug: redefine memory offline retry logic Michal Hocko
2017-09-18  7:08 ` [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early Michal Hocko
2017-10-10 12:05   ` Michael Ellerman
2017-10-10 12:27     ` Michal Hocko
2017-10-11  2:37       ` Michael Ellerman
2017-10-11  5:19         ` Michael Ellerman
2017-10-11 14:05           ` Anshuman Khandual
2017-10-11 14:16             ` Michal Hocko
2017-10-11  6:51         ` Michal Hocko
2017-10-11  8:04           ` Vlastimil Babka
2017-10-11  8:13             ` Michal Hocko
2017-10-11 11:17               ` Vlastimil Babka
2017-10-11 11:24                 ` Michal Hocko
2017-10-13 11:42             ` Michael Ellerman
2017-10-13 11:58               ` Michal Hocko
2017-10-13 12:00                 ` [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages Michal Hocko
2017-10-13 12:00                   ` [PATCH 2/2] mm, page_alloc: fail has_unmovable_pages when seeing reserved pages Michal Hocko
2017-10-13 12:04                     ` Vlastimil Babka
2017-10-13 12:07                       ` Michal Hocko
2017-10-17 13:03                         ` Vlastimil Babka
2017-10-17 11:41                   ` [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages Michael Ellerman
2017-10-17 12:03                     ` Michal Hocko
2017-10-17 13:02                   ` Vlastimil Babka
2017-10-19  2:51                   ` Joonsoo Kim
2017-10-19  7:15                     ` Michal Hocko
2017-10-19  7:33                       ` Joonsoo Kim
2017-10-19  8:20                         ` Michal Hocko
2017-10-19 12:21                           ` Michal Hocko
2017-10-20  2:13                             ` Joonsoo Kim
2017-10-20  5:59                               ` Michal Hocko
2017-10-20  6:50                                 ` Joonsoo Kim
2017-10-20  7:02                                   ` Michal Hocko
2017-10-23  5:23                                     ` Joonsoo Kim
2017-10-23  8:10                                       ` Michal Hocko
2017-10-24  4:44                                         ` Joonsoo Kim
2017-10-24  7:44                                           ` Michal Hocko
2017-10-24  8:12                                           ` Vlastimil Babka
2017-10-24 12:25                                             ` Michal Hocko [this message]
2017-10-26  2:47                                             ` Joonsoo Kim
2017-10-26  7:41                                               ` Michal Hocko
2017-10-20  7:22                               ` Xishi Qiu
2017-10-20  8:17                                 ` Michal Hocko
2017-10-23  5:26                                   ` Joonsoo Kim
2017-10-26 13:04                             ` Vlastimil Babka
2017-10-26 13:59                             ` Michal Hocko
2017-09-18  7:08 ` [PATCH 2/2] mm, memory_hotplug: remove timeout from __offline_memory Michal Hocko
     [not found] <AM3PR04MB14892A9D6D2FBCE21B8C1F0FF12B0@AM3PR04MB1489.eurprd04.prod.outlook.com>
2017-11-13  7:33 ` [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages Ran Wang
2017-11-13 11:02   ` Michal Hocko
2017-11-14  6:10     ` Ran Wang
2017-11-14  7:06       ` Michal Hocko
2017-11-14  7:45         ` Ran Wang

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