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Re: review [1 of 3]: lazy superblock counters - core kernel

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: review [1 of 3]: lazy superblock counters - core kernel
From: David Chinner <dgc@xxxxxxx>
Date: Tue, 24 Apr 2007 09:20:02 +1000
Cc: David Chinner <dgc@xxxxxxx>, xfs-dev <xfs-dev@xxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <20070423222340.GA23870@infradead.org>
References: <20070419231459.GX48531920@melbourne.sgi.com> <20070423220010.GA18325@infradead.org> <20070423221622.GL32602149@melbourne.sgi.com> <20070423222340.GA23870@infradead.org>
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On Mon, Apr 23, 2007 at 11:23:40PM +0100, Christoph Hellwig wrote:
> On Tue, Apr 24, 2007 at 08:16:23AM +1000, David Chinner wrote:
> > > > +                       INT_SET(sb->sb_fdblocks, ARCH_CONVERT, 
> > > > mp->m_sb.sb_fdblocks);
> > > > +                       XFS_SB_UNLOCK(mp, s);
> > > 
> > > This is really quite nasty.  Should we at least force a cache flush here?
> > 
> > Well, that is what it's doing - xfs_log_sbcount() flushes the counters and
> > logs the changes to the superblock. If that fails (very rare) we've already
> > got the current values in mp->m_sb and so all we need to do is push them
> > into the disk superblock and write it.
> 
> Sorry, should have been more detailed.  I meant the disk cache, as in
> blkdev_issue_flush, to make sure the data hits the disk, even if it doesn't
> go through a transaction which would normally do that. (in the barriers case)

Ah, gotcha. Hmmm - if this is necessary, I may as well add the flush to
the closing of the buftargs - that way we will always be certain that
an unmount leaves everything on disk and not in disk caches. That sounds
like a better approach to me than putting an explicit flush in this
particular case. Sound fair?

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group


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