From: Joonsoo Kim <js1304@gmail.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@lge.com, Vlastimil Babka <vbabka@suse.cz>,
Christoph Hellwig <hch@infradead.org>,
Roman Gushchin <guro@fb.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH v4 05/11] mm/migrate: clear __GFP_RECLAIM for THP allocation for migration
Date: Wed, 8 Jul 2020 16:19:17 +0900 [thread overview]
Message-ID: <20200708071916.GD16543@js1304-desktop> (raw)
In-Reply-To: <20200707114019.GI5913@dhcp22.suse.cz>
On Tue, Jul 07, 2020 at 01:40:19PM +0200, Michal Hocko wrote:
> On Tue 07-07-20 16:44:43, Joonsoo Kim wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> >
> > In mm/migrate.c, THP allocation for migration is called with the provided
> > gfp_mask | GFP_TRANSHUGE. This gfp_mask contains __GFP_RECLAIM and it
> > would be conflict with the intention of the GFP_TRANSHUGE.
> >
> > GFP_TRANSHUGE/GFP_TRANSHUGE_LIGHT is introduced to control the reclaim
> > behaviour by well defined manner since overhead of THP allocation is
> > quite large and the whole system could suffer from it. So, they deals
> > with __GFP_RECLAIM mask deliberately. If gfp_mask contains __GFP_RECLAIM
> > and uses gfp_mask | GFP_TRANSHUGE(_LIGHT) for THP allocation, it means
> > that it breaks the purpose of the GFP_TRANSHUGE(_LIGHT).
>
> GFP_TRANSHUGE* is not a carved in stone design. Their primary reason to
> exist is to control how hard to try for different allocation
> paths/configurations because their latency expectations might be
> largerly different. It is mostly the #PF path which aims to be as
> lightweight as possible I believe nobody simply considered migration to be
> very significant to even care. And I am still not sure it matters but
> I would tend to agree that a consistency here is probably a very minor
> plus.
>
> Your changelog is slightly misleading in that regard because it suggests
> that this is a real problem while it doesn't present any actual data.
> It would be really nice to make the effective change really stand out.
> We are only talking about __GFP_RECLAIM_KSWAPD here. So the only
> difference is that the migration won't wake up kswapd now.
>
> All that being said the changelog should be probably more explicit about
> the fact that this is solely done for consistency and be honest that the
> runtime effect is not really clear. This would help people reading it in
> future.
Okay. How about following changelog?
Thanks.
----------->8--------------------
Subject: [PATCH] mm/migrate: clear __GFP_RECLAIM for THP allocation for
migration
In migration target allocation functions, THP allocations uses different
gfp_mask, especially, in regard to the reclaim gfp_mask. There is no
reason to use different reclaim gfp_mask for each cases and it is
an obstacle to make a common function in order to clean-up migration
target allocation functions. This patch fixes this situation by using
common reclaim gfp_mask for THP allocation.
next prev parent reply other threads:[~2020-07-08 7:19 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-07 7:44 [PATCH v4 00/11] clean-up the migration target allocation functions js1304
2020-07-07 7:44 ` [PATCH v4 01/11] mm/page_isolation: prefer the node of the source page js1304
2020-07-07 7:44 ` [PATCH v4 02/11] mm/migrate: move migration helper from .h to .c js1304
2020-07-07 7:44 ` [PATCH v4 03/11] mm/hugetlb: unify migration callbacks js1304
2020-07-07 11:05 ` Vlastimil Babka
2020-07-07 11:19 ` Michal Hocko
2020-07-07 7:44 ` [PATCH v4 04/11] mm/hugetlb: make hugetlb migration callback CMA aware js1304
2020-07-07 11:22 ` Vlastimil Babka
2020-07-08 7:16 ` Joonsoo Kim
2020-07-08 7:41 ` Michal Hocko
2020-07-08 9:26 ` Vlastimil Babka
2020-07-08 10:57 ` Aneesh Kumar K.V
2020-07-08 11:32 ` Michal Hocko
2020-07-09 6:43 ` Michal Hocko
2020-07-09 7:03 ` Joonsoo Kim
2020-07-09 0:27 ` Mike Kravetz
2020-07-07 11:31 ` Michal Hocko
2020-07-08 6:48 ` Michal Hocko
2020-07-08 7:12 ` Joonsoo Kim
2020-07-07 7:44 ` [PATCH v4 05/11] mm/migrate: clear __GFP_RECLAIM for THP allocation for migration js1304
2020-07-07 11:40 ` Michal Hocko
2020-07-08 7:19 ` Joonsoo Kim [this message]
2020-07-08 7:48 ` Michal Hocko
2020-07-09 3:26 ` Joonsoo Kim
2020-07-07 12:17 ` Vlastimil Babka
2020-07-08 7:17 ` Joonsoo Kim
2020-07-09 7:17 ` Joonsoo Kim
2020-07-07 7:44 ` [PATCH v4 06/11] mm/migrate: make a standard migration target allocation function js1304
2020-07-07 11:43 ` Michal Hocko
2020-07-07 14:49 ` Vlastimil Babka
2020-07-07 19:00 ` Michal Hocko
2020-07-09 7:15 ` Joonsoo Kim
2020-07-09 10:28 ` Michal Hocko
2020-07-07 7:44 ` [PATCH v4 07/11] mm/gup: use a standard migration target allocation callback js1304
2020-07-07 11:46 ` Michal Hocko
2020-07-08 7:21 ` Joonsoo Kim
2020-07-07 7:44 ` [PATCH v4 08/11] mm/mempolicy: " js1304
2020-07-07 7:44 ` [PATCH v4 09/11] mm/page_alloc: remove a wrapper for alloc_migration_target() js1304
2020-07-07 7:44 ` [PATCH v4 10/11] mm/memory-failure: " js1304
2020-07-07 11:48 ` Michal Hocko
2020-07-07 15:03 ` Vlastimil Babka
2020-07-07 18:55 ` Michal Hocko
2020-07-07 15:00 ` Vlastimil Babka
2020-07-07 7:44 ` [PATCH v4 11/11] mm/memory_hotplug: " js1304
2020-07-07 11:52 ` Michal Hocko
2020-07-07 15:09 ` Vlastimil Babka
2020-07-09 3:25 ` Joonsoo Kim
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