Date:	Tue, 10 May 2011 14:38:19 +0200
From:	Jan Kara <jack@...e.cz>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	"Darrick J. Wong" <djwong@...ibm.com>,
	Theodore Tso <tytso@....edu>, Jan Kara <jack@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jens Axboe <axboe@...nel.dk>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jeff Layton <jlayton@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org,
	Chris Mason <chris.mason@...cle.com>,
	Joel Becker <jlbec@...lplan.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, Mingming Cao <mcao@...ibm.com>
Subject: Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during
 writeback for various fses

On Tue 10-05-11 10:59:15, OGAWA Hirofumi wrote:
> "Darrick J. Wong" <djwong@...ibm.com> writes:
> 
> > To assess the performance impact of stable page writes, I moved to a disk that
> > doesn't have DIF support so that I could measure just the impact of waiting for
> > writeback.  I first ran wac with 64 threads madly scribbling on a 64k file and
> > saw about a 12 percent performance decrease.  I then reran the wac program with
> > 64 threads and a 64MB file and saw about the same performance numbers.  As I
> > suspected, the patchset only seems to impact workloads that rewrite the same
> > memory page frequently.
> >
> > I am still chasing down what exactly is broken in ext3.  data=writeback mode
> > passes with no failures.  data=ordered, however, does not pass; my current
> > suspicion is that jbd is calling submit_bh on data buffers but doesn't call
> > page_mkclean to kick the userspace programs off the page before writing it.
> >
> > Per various comments regarding v3 of this patchset, I've integrated his
> > suggestions, reworked the patch descriptions to make it clearer which ones
> > touch all the filesystems and which ones are to fix remaining holes in specific
> > filesystems, and expanded the scope of filesystems that got fixed.
> >
> > As always, questions and comments are welcome; and thank you to all the
> > previous reviewers of this patchset.  I am also soliciting people's opinions on
> > whether or not these patches could go upstream for .40.
> 
> I'd like to know those patches are on what state. Waiting in writeback
> page makes slower, like you mentioned it (I guess it would more
> noticeable if device was slower that like FAT uses). And I think
> currently it doesn't help anything others for blk-integrity stuff
> (without other technic, it doesn't help FS consistency)?
> 
> So, why is this locking stuff enabled always? I think it would be better
> to enable only if blk-integrity stuff was enabled.
> 
> If it was more sophisticate but more complex stuff (e.g. use
> copy-on-write technic for it), I would agree always enable though.
  Well, also software RAID generally needs this feature (so that parity
information / mirror can be properly kept in sync). Not that I'd advocate
that this feature must be always enabled, it's just that there are also
other users besides blk-integrity.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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