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
