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Re: [PATCH] xfs: Don't flush inodes when project quota exceeded

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH] xfs: Don't flush inodes when project quota exceeded
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 22 Nov 2012 09:09:50 +1100
Cc: Jan Kara <jack@xxxxxxx>, Ben Myers <bpm@xxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <50ACF289.2080901@xxxxxxxxxx>
References: <1352766973-14197-1-git-send-email-jack@xxxxxxx> <20121119213913.GB29498@xxxxxxxxxxxxx> <20121120161511.GE27055@xxxxxxx> <20121120170354.GF1408@xxxxxxxxxxxxx> <20121120202038.GF2591@dastard> <50ABF54E.6070508@xxxxxxxxxx> <20121120222215.GH2591@dastard> <50ACF289.2080901@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Nov 21, 2012 at 10:26:01AM -0500, Brian Foster wrote:
> On 11/20/2012 05:22 PM, Dave Chinner wrote:
> > On Tue, Nov 20, 2012 at 04:25:34PM -0500, Brian Foster wrote:
> >> Otherwise, unless I'm mistaken it sounds like we can use the existing
> >> eofblocks scan on user/group EDQUOT situations.
> > 
> > That we can. And for the project case, it's a simply and extra flag
> > and a call to filemap_flush() to do an async writeback before
> > trimming the specualtive preallocation.
> This makes sense generally. I'll need to dig further into this code to
> wrap my head around it. If my current understanding is correct, it
> sounds like we could do the same thing in general, non-quota ENOSPC
> handling, right? E.g., an unfiltered eofblocks scan (plus the flush bit)
> followed by a retry, rather than a complete flush of all dirty inodes.

Possibly, though we can also have dirty inodes that don't have
speculative prealloc (e.g. hole filling writes) and we really need to
flush them at ENOSPC, too. In general, I think the real ENOSPC case
needs the big hammer because we have to reclaim every last piece of
unnecessary reservation as possible to allow anything to proceed.
Porject quota ENOSPC isn't such a problem here, as there's still
other free space in the filesystem that allow normal operation to
take place...


Dave Chinner

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