linux-kernel - Re: [PATCH] Increase default MLOCK

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Date:   Tue, 23 Nov 2021 23:04:04 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Jason Gunthorpe <jgg@...pe.ca>,
        David Hildenbrand <david@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Andrew Dona-Couch <andrew@...acou.ch>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Drew DeVault <sir@...wn.com>,
        Ammar Faizi <ammarfaizi2@...weeb.org>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        io_uring Mailing List <io-uring@...r.kernel.org>,
        Pavel Begunkov <asml.silence@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB

On 11/23/21 18:00, Jason Gunthorpe wrote:
> 
>> believe what you say and I trust your experience :) So could as well be
>> that on such a "special" (or not so special) systems there should be a
>> way to restrict it to privileged users only.
> 
> At this point RDMA is about as "special" as people running large
> ZONE_MOVABLE systems, and the two are going to start colliding
> heavily. The RDMA VFIO migration driver should be merged soon which
> makes VMs using this stuff finally practical.

How does that work, I see the word migration, so does it cause pages to
be migrated out of ZONE_MOVABLE before they are pinned?
Similarly for io-uring we could be migrating pages to be pinned so that
the end up consolidated close together, and prevent pathologic
situations like in David's reproducer. IIRC that was a idea to do for
long-term pins in general.

> Jason
>