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Re: [PATCH 7/8] xfs: remove the per-filesystem list of dquots

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 7/8] xfs: remove the per-filesystem list of dquots
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Mon, 20 Feb 2012 17:19:15 -0500
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20120220221509.GE3592@dastard>
References: <20120220022815.018921977@xxxxxxxxxxxxxxxxxxxxxx> <20120220022904.615605871@xxxxxxxxxxxxxxxxxxxxxx> <20120220221509.GE3592@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Feb 21, 2012 at 09:15:09AM +1100, Dave Chinner wrote:
> On Sun, Feb 19, 2012 at 09:28:22PM -0500, Christoph Hellwig wrote:
> > Instead of keeping a separate per-filesystem list of dquots we can walk
> > the radix tree for the two places where we need to iterate all quota
> > structures.
> > 
> > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> Still a bit of a lookup vs iterate hold-off remaining, but I think
> we can live with the reduction now. If it proves to be a noticable
> problem then we can look towards RCU based lookups, I think.
> Otherwise it looks OK to me.

We only walk the list during:

  - mount time for quotacheck
  - umount time
  - full quotaoff

in the first two cases lookups can't happen at all, and in the latter
they at least shoudn't get this far.  So I really don't think it's
a problem.  And the full quotaoff even for quota accounting is something
I'd like to remove sooner or later, it just causes a lot of corner cases
for very little gain.

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