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Date: Fri, 18 Dec 2020 07:24:53 -0500 From: Pavel Tatashin <pasha.tatashin@...een.com> To: Michal Hocko <mhocko@...e.com> Cc: LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>, David Hildenbrand <david@...hat.com>, Oscar Salvador <osalvador@...e.de>, Dan Williams <dan.j.williams@...el.com>, Sasha Levin <sashal@...nel.org>, Tyler Hicks <tyhicks@...ux.microsoft.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, mike.kravetz@...cle.com, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>, Peter Zijlstra <peterz@...radead.org>, Mel Gorman <mgorman@...e.de>, Matthew Wilcox <willy@...radead.org>, David Rientjes <rientjes@...gle.com>, John Hubbard <jhubbard@...dia.com>, Linux Doc Mailing List <linux-doc@...r.kernel.org>, Ira Weiny <ira.weiny@...el.com>, linux-kselftest@...r.kernel.org Subject: Re: [PATCH v4 05/10] mm/gup: migrate pinned pages out of movable zone On Fri, Dec 18, 2020 at 4:43 AM Michal Hocko <mhocko@...e.com> wrote: > > On Thu 17-12-20 13:52:38, Pavel Tatashin wrote: > > + * 1. Pinned pages: (long-term) pinning of movable pages is avoided > > + * when pages are pinned and faulted, but it is still possible that > > + * address space already has pages in ZONE_MOVABLE at the time when > > + * pages are pinned (i.e. user has touches that memory before > > + * pinning). In such case we try to migrate them to a different zone, > > + * but if migration fails the pages can still end-up pinned in > > + * ZONE_MOVABLE. In such case, memory offlining might retry a long > > + * time and will only succeed once user application unpins pages. > > I still dislike this. Pinning can fail so there shouldn't be any reasons > to break MOVABLE constrain for something that can be handled. If > anything there should be a very good reasoning behind this decision > documented. This is basically current behaviour, after patch 8, we can never pin pages in the movable zone, so I will update this comment in that patch. Thank you, Pasha > -- > Michal Hocko > SUSE Labs
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