From: Jens Axboe <[email protected]>
To: Vito Caputo <[email protected]>
Cc: Matthew Wilcox <[email protected]>,
Andrew Morton <[email protected]>,
Ammar Faizi <[email protected]>,
Drew DeVault <[email protected]>,
[email protected], [email protected],
io_uring Mailing List <[email protected]>,
Pavel Begunkov <[email protected]>,
[email protected]
Subject: Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB
Date: Tue, 16 Nov 2021 12:41:00 -0700 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 11/16/21 12:21 PM, Vito Caputo wrote:
> 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.
You don't need to register any buffers, and I don't expect any basic
uses cases to do so. Which means that the 8MB just need to cover the
ring itself, and you can fit a _lot_ of rings into 8MB. The memlock
limit only applies to buffers if you register them, not for any "normal"
use cases where you just pass buffers for read/write or O_DIRECT
read/write.
> 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.
I just don't want to turn this into a bikeshedding conversation. I'm
fine with making it autoscale obviously, but who's going to do the work?
> As an upper bound I'd probably look at the highest anticipated
> consumer resolutions, and handle a couple fullscreen 32bpp instances
> being pinned.
Not sure I see the relevance here.
--
Jens Axboe
next prev parent reply other threads:[~2021-11-16 19:41 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-28 8:08 [PATCH] Increase default MLOCK_LIMIT to 8 MiB Drew DeVault
2021-10-28 18:22 ` Jens Axboe
2021-11-04 14:27 ` Cyril Hrubis
2021-11-04 14:44 ` Jens Axboe
2021-11-06 2:33 ` Ammar Faizi
2021-11-06 7:05 ` Drew DeVault
2021-11-06 7:12 ` Ammar Faizi
2021-11-16 4:35 ` Andrew Morton
2021-11-16 6:32 ` Drew DeVault
2021-11-16 19:47 ` Andrew Morton
2021-11-16 19:48 ` Drew DeVault
2021-11-16 21:37 ` Andrew Morton
2021-11-17 8:23 ` Drew DeVault
2021-11-22 17:11 ` David Hildenbrand
2021-11-22 17:55 ` Andrew Dona-Couch
2021-11-22 18:26 ` David Hildenbrand
2021-11-22 19:53 ` Jens Axboe
2021-11-22 20:03 ` Matthew Wilcox
2021-11-22 20:04 ` Jens Axboe
2021-11-22 20:08 ` David Hildenbrand
2021-11-22 20:44 ` Jens Axboe
2021-11-22 21:56 ` David Hildenbrand
2021-11-23 12:02 ` David Hildenbrand
2021-11-23 13:25 ` Jason Gunthorpe
2021-11-23 13:39 ` David Hildenbrand
2021-11-23 14:07 ` Jason Gunthorpe
2021-11-23 14:44 ` David Hildenbrand
2021-11-23 17:00 ` Jason Gunthorpe
2021-11-23 17:04 ` David Hildenbrand
2021-11-23 22:04 ` Vlastimil Babka
2021-11-23 23:59 ` Jason Gunthorpe
2021-11-24 8:57 ` David Hildenbrand
2021-11-24 13:23 ` Jason Gunthorpe
2021-11-24 13:25 ` David Hildenbrand
2021-11-24 13:28 ` Jason Gunthorpe
2021-11-24 13:29 ` David Hildenbrand
2021-11-24 13:48 ` Jason Gunthorpe
2021-11-24 14:14 ` David Hildenbrand
2021-11-24 15:34 ` Jason Gunthorpe
2021-11-24 16:43 ` David Hildenbrand
2021-11-24 18:35 ` Jason Gunthorpe
2021-11-24 19:09 ` David Hildenbrand
2021-11-24 23:11 ` Jason Gunthorpe
2021-11-30 15:52 ` David Hildenbrand
2021-11-24 18:37 ` David Hildenbrand
2021-11-24 14:37 ` Vlastimil Babka
2021-11-24 14:41 ` David Hildenbrand
2021-11-16 18:36 ` Matthew Wilcox
2021-11-16 18:44 ` Drew DeVault
2021-11-16 18:55 ` Jens Axboe
2021-11-16 19:21 ` Vito Caputo
2021-11-16 19:25 ` Drew DeVault
2021-11-16 19:46 ` Vito Caputo
2021-11-16 19:41 ` Jens Axboe [this message]
2021-11-17 22:26 ` Johannes Weiner
2021-11-17 23:17 ` Jens Axboe
2021-11-18 21:58 ` Andrew Morton
2021-11-19 7:41 ` Drew DeVault
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