linux-kernel - Re: Pinning ZONE

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Message-ID: <20201123183418.GB5487@ziepe.ca>
Date:   Mon, 23 Nov 2020 14:34:18 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     Michal Hocko <mhocko@...e.com>, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>,
        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>,
        Stephen Hemminger <sthemmin@...rosoft.com>
Subject: Re: Pinning ZONE_MOVABLE pages

On Mon, Nov 23, 2020 at 12:54:16PM -0500, Pavel Tatashin wrote:
> > 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.
> 
> That is right, as the first step we could just do fault and immediate
> migration, which is silly, but still better than what we have now.

I was looking at this CMA code lately and would love to see a
cleaner/faster implementation.

If you really understand how this works maybe it is an opportunity to
make it all work better.

Jason