From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1E231C433EF for ; Tue, 16 Nov 2021 19:21:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 02ED4619E5 for ; Tue, 16 Nov 2021 19:21:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234139AbhKPTYr (ORCPT ); Tue, 16 Nov 2021 14:24:47 -0500 Received: from shells.gnugeneration.com ([66.240.222.126]:48288 "EHLO shells.gnugeneration.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239590AbhKPTYr (ORCPT ); Tue, 16 Nov 2021 14:24:47 -0500 Received: by shells.gnugeneration.com (Postfix, from userid 1000) id 468601A40175; Tue, 16 Nov 2021 11:21:48 -0800 (PST) Date: Tue, 16 Nov 2021 11:21:48 -0800 From: Vito Caputo To: Jens Axboe Cc: Matthew Wilcox , Andrew Morton , Ammar Faizi , Drew DeVault , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, io_uring Mailing List , Pavel Begunkov , linux-mm@kvack.org Subject: Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB Message-ID: <20211116192148.vjdlng7pesbgjs6b@shells.gnugeneration.com> References: <20211028080813.15966-1-sir@cmpwn.com> <593aea3b-e4a4-65ce-0eda-cb3885ff81cd@gnuweeb.org> <20211115203530.62ff33fdae14927b48ef6e5f@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Tue, Nov 16, 2021 at 11:55:41AM -0700, Jens Axboe wrote: > On 11/16/21 11:36 AM, Matthew Wilcox wrote: > > On Mon, Nov 15, 2021 at 08:35:30PM -0800, Andrew Morton wrote: > >> I'd also be interested in seeing feedback from the MM developers. > > [...] > >> Subject: Increase default MLOCK_LIMIT to 8 MiB > > > > On the one hand, processes can already allocate at least this much > > memory that is non-swappable, just by doing things like opening a lot of > > files (allocating struct file & fdtable), using a lot of address space > > (allocating page tables), so I don't have a problem with it per se. > > > > On the other hand, 64kB is available on anything larger than an IBM XT. > > Linux will still boot on machines with 4MB of RAM (eg routers). For > > someone with a machine with only, say, 32MB of memory, this allows a > > process to make a quarter of the memory unswappable, and maybe that's > > not a good idea. So perhaps this should scale over a certain range? > > > > Is 8MB a generally useful amount of memory for an iouring user anyway? > > If you're just playing with it, sure, but if you have, oh i don't know, > > a database, don't you want to pin the entire cache and allow IO to the > > whole thing? > > 8MB is plenty for most casual use cases, which is exactly the ones that > we want to "just work" without requiring weird system level > modifications to increase the memlock limit. > Considering a single fullscreen 32bpp 4K-resolution framebuffer is ~32MiB, I'm not convinced this is really correct in nearly 2022. If we're going to bump the default at the kernel, I'm with Matthew on making it autoscale within a sane range, depending on available memory. As an upper bound I'd probably look at the highest anticipated consumer resolutions, and handle a couple fullscreen 32bpp instances being pinned. Regards, Vito Caputo