From: Michal Hocko <mhocko@suse.com>
To: Joonsoo Kim <js1304@gmail.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
David Hildenbrand <david@redhat.com>,
Oscar Salvador <osalvador@suse.de>,
Dan Williams <dan.j.williams@intel.com>,
Sasha Levin <sashal@kernel.org>,
Tyler Hicks <tyhicks@linux.microsoft.com>,
mike.kravetz@oracle.com, Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Mel Gorman <mgorman@suse.de>,
Matthew Wilcox <willy@infradead.org>,
David Rientjes <rientjes@google.com>,
John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH 0/6] prohibit pinning pages in ZONE_MOVABLE
Date: Mon, 7 Dec 2020 13:13:07 +0100 [thread overview]
Message-ID: <20201207121307.GG25569@dhcp22.suse.cz> (raw)
In-Reply-To: <20201207071238.GA10731@js1304-desktop>
On Mon 07-12-20 16:12:50, Joonsoo Kim wrote:
> On Fri, Dec 04, 2020 at 12:50:56PM -0500, Pavel Tatashin wrote:
> > > > Yes, this indeed could be a problem for some configurations. I will
> > > > add your comment to the commit log of one of the patches.
> > >
> > > It sounds like there is some inherent tension here, breaking THP's
> > > when doing pin_user_pages() is a really nasty thing to do. DMA
> > > benefits greatly from THP.
> > >
> > > I know nothing about ZONE_MOVABLE, is this auto-setup or an admin
> > > option? If the result of this patch is standard systems can no longer
> > > pin > 80% of their memory I have some regression concerns..
> >
> > ZONE_MOVABLE can be configured via kernel parameter, or when memory
> > nodes are onlined after hot-add; so this is something that admins
> > configure. ZONE_MOVABLE is designed to gurantee memory hot-plug
>
> Just note, the origin of ZONE_MOVABLE is to provide availability of
> huge page, especially, hugetlb page. AFAIK, not guarantee memory
> hot-plug. See following commit that introduces the ZONE_MOVABLE.
>
> 2a1e274 Create the ZONE_MOVABLE zone
>
> > functionality, and not availability of THP, however, I did not know
> > about the use case where some admins might configure ZONE_MOVABLE to
>
> The usecase is lightly mentioned in previous discussion.
>
> http://lkml.kernel.org/r/alpine.DEB.2.23.453.2011221300100.2830030@chino.kir.corp.google.com
>
> Anyway, I agree with your other arguments and this patchset.
Yes, historically the original motivation for the movable zone was to
help creating large pages via compaction. I also do remember Mel
not being particularly happy about that.
The thing is that the movability constrain is just too strict for this
usecases because the movable zone, especially a lot of it, might be
causing similar to lowmem/highmem problems very well known from 32b
world. So an admin had to be always very careful when configuring to not
cause zone pressure problems.
Later on, with a higher demand on the memory hotplug - especially the
hotremove usecases - it has become clear that the only reliable way for
the memory offlining is to rule out any unmovable memory out of the way
and that is why a rather strong properly of movable zone was relied on.
In the end we are in two rather different requirements here. One for
optimization and one for correctness. In this case I would much rather
focus on the correctness aspect.
--
Michal Hocko
SUSE Labs
prev parent reply other threads:[~2020-12-07 12:13 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-02 5:23 [PATCH 0/6] prohibit pinning pages in ZONE_MOVABLE Pavel Tatashin
2020-12-02 5:23 ` [PATCH 1/6] mm/gup: perform check_dax_vmas only when FS_DAX is enabled Pavel Tatashin
2020-12-02 16:22 ` Ira Weiny
2020-12-02 18:15 ` Pavel Tatashin
2020-12-02 16:29 ` Jason Gunthorpe
2020-12-02 18:16 ` Pavel Tatashin
2020-12-03 7:59 ` John Hubbard
2020-12-03 14:52 ` Pavel Tatashin
2020-12-02 5:23 ` [PATCH 2/6] mm/gup: don't pin migrated cma pages in movable zone Pavel Tatashin
2020-12-02 16:31 ` David Hildenbrand
2020-12-02 18:17 ` Pavel Tatashin
2020-12-03 8:01 ` John Hubbard
2020-12-03 8:46 ` Michal Hocko
2020-12-03 14:58 ` Pavel Tatashin
2020-12-02 5:23 ` [PATCH 3/6] mm/gup: make __gup_longterm_locked common Pavel Tatashin
2020-12-02 16:31 ` Ira Weiny
2020-12-02 16:33 ` Ira Weiny
2020-12-02 18:19 ` Pavel Tatashin
2020-12-03 0:03 ` Pavel Tatashin
2020-12-03 8:03 ` John Hubbard
2020-12-03 15:02 ` Pavel Tatashin
2020-12-02 5:23 ` [PATCH 4/6] mm cma: rename PF_MEMALLOC_NOCMA to PF_MEMALLOC_NOMOVABLE Pavel Tatashin
2020-12-03 8:04 ` John Hubbard
2020-12-03 15:02 ` Pavel Tatashin
2020-12-03 8:57 ` Michal Hocko
2020-12-03 15:02 ` Pavel Tatashin
2020-12-02 5:23 ` [PATCH 5/6] mm: honor PF_MEMALLOC_NOMOVABLE for all allocations Pavel Tatashin
2020-12-03 8:17 ` John Hubbard
2020-12-03 15:06 ` Pavel Tatashin
2020-12-03 16:51 ` John Hubbard
2020-12-03 9:17 ` Michal Hocko
2020-12-03 15:15 ` Pavel Tatashin
2020-12-04 8:43 ` Michal Hocko
2020-12-04 8:54 ` Michal Hocko
2020-12-04 16:07 ` Pavel Tatashin
2020-12-02 5:23 ` [PATCH 6/6] mm/gup: migrate pinned pages out of movable zone Pavel Tatashin
2020-12-02 16:35 ` Jason Gunthorpe
2020-12-03 0:19 ` Pavel Tatashin
2020-12-03 1:08 ` Jason Gunthorpe
2020-12-03 1:34 ` Pavel Tatashin
2020-12-03 14:17 ` Jason Gunthorpe
2020-12-03 16:40 ` Pavel Tatashin
2020-12-03 16:59 ` Jason Gunthorpe
2020-12-03 17:14 ` Pavel Tatashin
2020-12-03 19:15 ` Pavel Tatashin
2020-12-03 19:36 ` Jason Gunthorpe
2020-12-04 16:24 ` Pavel Tatashin
2020-12-04 17:06 ` Jason Gunthorpe
2020-12-04 20:05 ` Daniel Jordan
2020-12-04 20:16 ` Pavel Tatashin
2020-12-08 2:27 ` Daniel Jordan
2020-12-04 20:52 ` Jason Gunthorpe
2020-12-08 2:48 ` Daniel Jordan
2020-12-08 13:24 ` Jason Gunthorpe
2020-12-03 8:22 ` John Hubbard
2020-12-03 15:55 ` Pavel Tatashin
2020-12-04 4:13 ` Joonsoo Kim
2020-12-04 17:43 ` Pavel Tatashin
2020-12-07 7:13 ` Joonsoo Kim
2020-12-04 4:02 ` [PATCH 0/6] prohibit pinning pages in ZONE_MOVABLE Joonsoo Kim
2020-12-04 15:55 ` Pavel Tatashin
2020-12-04 16:10 ` Jason Gunthorpe
2020-12-04 17:50 ` Pavel Tatashin
2020-12-04 18:01 ` David Hildenbrand
2020-12-04 18:10 ` Pavel Tatashin
2020-12-07 7:12 ` Joonsoo Kim
2020-12-07 12:13 ` Michal Hocko [this message]
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