From: Jens Axboe <axboe@kernel.dk>
To: Cyril Hrubis <chrubis@suse.cz>
Cc: Drew DeVault <sir@cmpwn.com>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
io-uring@vger.kernel.org, Pavel Begunkov <asml.silence@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB
Date: Thu, 4 Nov 2021 08:44:24 -0600 [thread overview]
Message-ID: <fdf1c610-6c9a-befd-a284-b8a552b4c225@kernel.dk> (raw)
In-Reply-To: <YYPt1PaGtiSLvyKw@rei>
On 11/4/21 8:27 AM, Cyril Hrubis wrote:
> Hi!
>>> This limit has not been updated since 2008, when it was increased to 64
>>> KiB at the request of GnuPG. Until recently, the main use-cases for this
>>> feature were (1) preventing sensitive memory from being swapped, as in
>>> GnuPG's use-case; and (2) real-time use-cases. In the first case, little
>>> memory is called for, and in the second case, the user is generally in a
>>> position to increase it if they need more.
>>>
>>> The introduction of IOURING_REGISTER_BUFFERS adds a third use-case:
>>> preparing fixed buffers for high-performance I/O. This use-case will
>>> take as much of this memory as it can get, but is still limited to 64
>>> KiB by default, which is very little. This increases the limit to 8 MB,
>>> which was chosen fairly arbitrarily as a more generous, but still
>>> conservative, default value.
>>> ---
>>> It is also possible to raise this limit in userspace. This is easily
>>> done, for example, in the use-case of a network daemon: systemd, for
>>> instance, provides for this via LimitMEMLOCK in the service file; OpenRC
>>> via the rc_ulimit variables. However, there is no established userspace
>>> facility for configuring this outside of daemons: end-user applications
>>> do not presently have access to a convenient means of raising their
>>> limits.
>>>
>>> The buck, as it were, stops with the kernel. It's much easier to address
>>> it here than it is to bring it to hundreds of distributions, and it can
>>> only realistically be relied upon to be high-enough by end-user software
>>> if it is more-or-less ubiquitous. Most distros don't change this
>>> particular rlimit from the kernel-supplied default value, so a change
>>> here will easily provide that ubiquity.
>>
>> Agree with raising this limit, it is ridiculously low and we often get
>> reports from people that can't even do basic rings with it. Particularly
>> when bpf is involved as well, as it also dips into this pool.
>>
>> On the production side at facebook, we do raise this limit as well.
>
> We are raising this limit to 2MB for LTP testcases as well, otherwise we
> get failures when we run a few bpf tests in quick succession.>
> Acked-by: Cyril Hrubis <chrubis@suse.cz>
Andrew, care to pick this one up for 5.16?
--
Jens Axboe
next prev parent reply other threads:[~2021-11-04 14:44 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 [this message]
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
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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