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Message-ID: <20190121214715.GA27713@redhat.com>
Date: Mon, 21 Jan 2019 16:47:15 -0500
From: Vivek Goyal <vgoyal@...hat.com>
To: Andrea Righi <righi.andrea@...il.com>
Cc: Josef Bacik <josef@...icpanda.com>, Tejun Heo <tj@...nel.org>,
Li Zefan <lizefan@...wei.com>,
Johannes Weiner <hannes@...xchg.org>,
Jens Axboe <axboe@...nel.dk>, Dennis Zhou <dennis@...nel.org>,
cgroups@...r.kernel.org, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] cgroup: fsio throttle controller
On Sat, Jan 19, 2019 at 11:08:27AM +0100, Andrea Righi wrote:
[..]
> Alright, let's skip the root cgroup for now. I think the point here is
> if we want to provide sync() isolation among cgroups or not.
>
> According to the manpage:
>
> sync() causes all pending modifications to filesystem metadata and cached file data to be
> written to the underlying filesystems.
>
> And:
> According to the standard specification (e.g., POSIX.1-2001), sync() schedules the writes, but
> may return before the actual writing is done. However Linux waits for I/O completions, and
> thus sync() or syncfs() provide the same guarantees as fsync called on every file in the sys‐
> tem or filesystem respectively.
>
> Excluding the root cgroup, do you think a sync() issued inside a
> specific cgroup should wait for I/O completions only for the writes that
> have been generated by that cgroup?
Can we account I/O towards the cgroup which issued "sync" only if write
rate of sync cgroup is higher than cgroup to which page belongs to. Will
that solve problem, assuming its doable?
Vivek
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