From: Jens Axboe <axboe@kernel.dk>
To: Michal Hocko <mhocko@kernel.org>, Jerome Glisse <jglisse@redhat.com>
Cc: lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, Benjamin LaHaise <bcrl@kvack.org>
Subject: Re: [LSF/MM/BPF TOPIC] Do not pin pages for various direct-io scheme
Date: Wed, 22 Jan 2020 08:12:51 -0700 [thread overview]
Message-ID: <015647b0-360c-c9ac-ac20-405ae0ec4512@kernel.dk> (raw)
In-Reply-To: <20200122115926.GW29276@dhcp22.suse.cz>
On 1/22/20 4:59 AM, Michal Hocko wrote:
> On Tue 21-01-20 20:57:23, Jerome Glisse wrote:
>> We can also discuss what kind of knobs we want to expose so that
>> people can decide to choose the tradeof themself (ie from i want low
>> latency io-uring and i don't care wether mm can not do its business; to
>> i want mm to never be impeded in its business and i accept the extra
>> latency burst i might face in io operations).
>
> I do not think it is a good idea to make this configurable. How can
> people sensibly choose between the two without deep understanding of
> internals?
Fully agree, we can't just punt this to a knob and call it good, that's
a typical fallacy of core changes. And there is only one mode for
io_uring, and that's consistent low latency. If this change introduces
weird reclaim, compaction or migration latencies, then that's a
non-starter as far as I'm concerned.
And what do those two settings even mean? I don't even know, and a user
sure as hell doesn't either.
io_uring pins two types of pages - registered buffers, these are used
for actual IO, and the rings themselves. The rings are not used for IO,
just used to communicate between the application and the kernel.
--
Jens Axboe
next prev parent reply other threads:[~2020-01-22 15:12 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 2:31 [LSF/MM/BPF TOPIC] Do not pin pages for various direct-io scheme jglisse
2020-01-22 3:54 ` Jens Axboe
2020-01-22 4:57 ` Jerome Glisse
2020-01-22 11:59 ` Michal Hocko
2020-01-22 15:12 ` Jens Axboe [this message]
2020-01-22 16:54 ` Jerome Glisse
2020-01-22 17:04 ` Jens Axboe
2020-01-22 17:28 ` Jerome Glisse
2020-01-22 17:38 ` Jens Axboe
2020-01-22 17:40 ` Jerome Glisse
2020-01-22 17:49 ` Jens Axboe
2020-01-27 19:01 ` Jason Gunthorpe
2020-01-22 4:19 ` Dan Williams
2020-01-22 5:00 ` Jerome Glisse
2020-01-22 15:56 ` [Lsf-pc] " Dan Williams
2020-01-22 17:02 ` Jerome Glisse
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