linux-ext4 - Re: Query about DIO/AIO WRITE throttling and ext4 serialization

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110603011129.GG16306@thunk.org>
Date:	Thu, 2 Jun 2011 21:11:29 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Dave Chinner <david@...morbit.com>, linux-ext4@...r.kernel.org
Subject: Re: Query about DIO/AIO WRITE throttling and ext4 serialization

On Thu, Jun 02, 2011 at 08:54:03PM -0400, Vivek Goyal wrote:
> 
> In this case I had done "sync" while aio-stress was doing O_DIRECT writes.
> I really don't have any real world example, I just cooked up a hypothetical
> scenario.
> 
> Just wondering why ext4 and XFS behavior are different and which is a
> more appropriate behavior. ext4 does not seem to be waiting for all
> pending AIO/DIO to finish while XFS does.

I think this is something we can chalk up to "different
implementations do different things".  I'm not convinced either
behviour is wrong per se.  Granted, the recent work to make sync and
fsync not livelock in the face of continuing writes means that I'm
more happy with ext4's behaviour, but I don't think that means xfs's
behavior is wrong.

One of the things that I have thought about is sysctl which makes sync
a no-op unless you are root.  The reason for that is that many system
administrators sometimes have a habit of typing sync, and on a heavily
loaded production server, this can really cause performance to go to
hell for up to tens of minutes.  So it might make sense to not allow
non-root users from trashing overall system performance by running
sync....

						- Ted
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html