linux-kernel - Re: [patch/rft] jbd2: tag journal writes as metadata I/O

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: <20100401194822.GA8401@atrey.karlin.mff.cuni.cz>
Date:	Thu, 1 Apr 2010 21:48:23 +0200
From:	Jan Kara <jack@...e.cz>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	jens.axboe@...cle.com, esandeen@...hat.com
Subject: Re: [patch/rft] jbd2: tag journal writes as metadata I/O

  Hi,

> In running iozone for writes to small files, we noticed a pretty big
> discrepency between the performance of the deadline and cfq I/O
> schedulers.  Investigation showed that I/O was being issued from 2
> different contexts: the iozone process itself, and the jbd2/sdh-8 thread
> (as expected).  Because of the way cfq performs slice idling, the delays
> introduced between the metadata and data I/Os were significant.  For
> example, cfq would see about 7MB/s versus deadline's 35 for the same
> workload.  I also tested fs_mark with writing and fsyncing 1000 64k
> files, and a similar 5x performance difference was observed.  Eric
> Sandeen suggested that I flag the journal writes as metadata, and once I
> did that, the performance difference went away completely (cfq has
> special logic to prioritize metadata I/O).
> 
> So, I'm submitting this patch for comments and testing.  I have a
> similar patch for jbd that I will submit if folks agree that this is a
> good idea.
  This looks like a good idea to me. I'd just be careful about data=journal
mode where even data is written via journal and thus you'd incorrectly
prioritize all the IO. I suppose that could have negative impact on performace
of other filesystems on the same disk. So for data=journal mode, I'd leave
write_op to be just WRITE / WRITE_SYNC_PLUG.

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/