From: Tejun Heo <tj@kernel.org>
To: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>,
cgroups@vger.kernel.org, xuejiufei <xuejiufei@gmail.com>,
kernel-team@fb.com, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2] writeback: synchronize sync(2) against cgroup writeback membership switches
Date: Wed, 13 Dec 2017 07:39:30 -0800 [thread overview]
Message-ID: <20171213153930.GO3919388@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <20171213110004.GB23068@quack2.suse.cz>
Hello,
On Wed, Dec 13, 2017 at 12:00:04PM +0100, Jan Kara wrote:
> OK, but this effectively prevents writeback from sync_inodes_sb() to ever
> make inode switch wbs. Cannot that be abused in some way like making sure
> writeback of our memcg is "invisible" by forcing it out using sync(2)? It
> just looks a bit dangerous to me...
That's true. There are a couple mitigating factors tho.
* While it can delay switching during sync(2), it'll all still be
recorded and the switch will happen soon if needed.
* sync(2) is hugely disruptive with or without this and can easily be
used to DOS the whole system. People are working on restricting the
blast radius of sync(2) to mitigate this problem, which most likely
make this a non-problem too.
If you can think of a better solution, I'm all ears.
Thanks.
--
tejun
next prev parent reply other threads:[~2017-12-13 15:39 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <dc694ae2-f07f-61e1-7097-7c8411cee12d@gmail.com>
[not found] ` <20171205182007.GV2421075@devbig577.frc2.facebook.com>
[not found] ` <8844b550-d91c-38d5-997a-a899d1e4aa42@gmail.com>
2017-12-11 19:50 ` [PATCH] writeback: synchronize sync(2) against cgroup writeback membership switches Tejun Heo
2017-12-12 6:04 ` xuejiufei
2017-12-12 16:30 ` Tejun Heo
2017-12-12 16:38 ` [PATCH v2] " Tejun Heo
2017-12-13 11:00 ` Jan Kara
2017-12-13 15:39 ` Tejun Heo [this message]
2017-12-19 13:04 ` Jan Kara
2017-12-19 13:31 ` Tejun Heo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20171213153930.GO3919388@devbig577.frc2.facebook.com \
--to=tj@kernel.org \
--cc=axboe@kernel.dk \
--cc=cgroups@vger.kernel.org \
--cc=jack@suse.cz \
--cc=kernel-team@fb.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=xuejiufei@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).