Message-ID: <dd92a69a-6d09-93a1-4f50-5020f5cc59d0@suse.cz>
Date:   Tue, 23 Nov 2021 23:04:04 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.2.0
Subject: Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB
Content-Language: en-US
To:     Jason Gunthorpe <jgg@ziepe.ca>,
        David Hildenbrand <david@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Andrew Dona-Couch <andrew@donacou.ch>,
        Andrew Morton <akpm@linux-foundation.org>,
        Drew DeVault <sir@cmpwn.com>,
        Ammar Faizi <ammarfaizi2@gnuweeb.org>,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        io_uring Mailing List <io-uring@vger.kernel.org>,
        Pavel Begunkov <asml.silence@gmail.com>, linux-mm@kvack.org
References: <20211116133750.0f625f73a1e4843daf13b8f7@linux-foundation.org>
 <b84bc345-d4ea-96de-0076-12ff245c5e29@redhat.com>
 <8f219a64-a39f-45f0-a7ad-708a33888a3b@www.fastmail.com>
 <333cb52b-5b02-648e-af7a-090e23261801@redhat.com>
 <ca96bb88-295c-ccad-ed2f-abc585cb4904@kernel.dk>
 <5f998bb7-7b5d-9253-2337-b1d9ea59c796@redhat.com>
 <20211123132523.GA5112@ziepe.ca>
 <10ccf01b-f13a-d626-beba-cbee70770cf1@redhat.com>
 <20211123140709.GB5112@ziepe.ca>
 <e4d7d211-5d62-df89-8f94-e49385286f1f@redhat.com>
 <20211123170056.GC5112@ziepe.ca>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20211123170056.GC5112@ziepe.ca>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

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
>