linux-kernel - Re: [PATCH v3 5/6] mm/gup: migrate pinned pages out of movable zone

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Date:   Mon, 14 Dec 2020 15:30:27 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        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>,
        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>
Subject: Re: [PATCH v3 5/6] mm/gup: migrate pinned pages out of movable zone

On Mon 14-12-20 15:21:21, David Hildenbrand wrote:
> On 14.12.20 14:36, Jason Gunthorpe wrote:
> > On Sat, Dec 12, 2020 at 08:29:11AM +0100, David Hildenbrand wrote:
> > 
> >>> Racing with another GUP in another thread is also not reasonable, so
> >>> failing to isolate can't be a failure
> >>
> >> Having VMs with multiple vfio containers is certainly realistic, and
> >> optimizing in user space to do vfio mappings concurrently doesn‘t
> >> sound too crazy to me. But I haven‘t checked if vfio common code
> >> already handles such concurrency.
> > 
> > There is a lot more out there than vfio.. RDMA already does concurrent
> > pin_user_pages in real apps
> 
> I actually misread your comment. I think we both agree that temporary
> isolation failures must not lead to a failure.

Yes, isolation failures are ephemeral. I believe that the migration
should start distinguishing between these and hard failures.
-- 
Michal Hocko
SUSE Labs