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Date:   Mon, 23 Nov 2020 13:15:02 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Pavel Tatashin <pasha.tatashin@soleen.com>
Cc:     Michal Hocko <mhocko@suse.com>, linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        LKML <linux-kernel@vger.kernel.org>,
        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>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, sthemmin@microsoft.com
Subject: Re: Pinning ZONE_MOVABLE pages
Message-ID: <20201123171502.GX244516@ziepe.ca>
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On Mon, Nov 23, 2020 at 11:06:21AM -0500, Pavel Tatashin wrote:

> What I mean here is allowing users to guarantee that the page's PA is
> going to stay the same. Sort of a stronger mlock. Mlock only
> guarantees that the page is not swapped, but something like

You've just described get/pin_user_pages(), that is exactly what it is
for.

I agree with the other emails, ZONE_MOVABLE needs to be reconciled
with FOLL_LONGTERM - most likely by preventing ZONE_MOVABLE pages from
being returned. This will need migration like CMA does and the point
about faulting is only an optimization to prevent fault then immediate
migration.

Jason