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

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Date:   Tue, 16 Nov 2021 11:46:44 -0800
From:   Vito Caputo <vcaputo@...garu.com>
To:     Drew DeVault <sir@...wn.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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 Tue, Nov 16, 2021 at 08:25:33PM +0100, Drew DeVault wrote:
> On Tue Nov 16, 2021 at 8:21 PM CET, Vito Caputo wrote:
> > Considering a single fullscreen 32bpp 4K-resolution framebuffer is
> > ~32MiB, I'm not convinced this is really correct in nearly 2022.
> 
> Can you name a practical use-case where you'll be doing I/O with
> uncompressed 4K framebuffers? The kind of I/O which is supported by
> io_uring, to be specific, not, say, handing it off to libdrm.

Obviously video/image editing software tends to operate on raw frames,
and sometimes even persists them via filesystems.

I haven't given it a lot of thought, but a framebuffer is a commonly
used unit of memory allocation in code run on the CPU I've written
over the years.  Being able to pin those for something like io_uring
(or some other DMA-possible interface) seems like an obvious
memory-hungry thing to consider here if we're talking default upper
bounds.

Regards,
Vito Caputo