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Re: [PATCH 04/11] xfs: call xfs_buf_delwri_queue directly

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 04/11] xfs: call xfs_buf_delwri_queue directly
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 2 Sep 2011 10:17:47 +1000
Cc: Alex Elder <aelder@xxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20110901214640.GB4579@xxxxxxxxxxxxx>
References: <20110823082802.335389799@xxxxxxxxxxxxxxxxxxxxxx> <20110823082912.512830398@xxxxxxxxxxxxxxxxxxxxxx> <1314904935.2903.62.camel@doink> <20110901214640.GB4579@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Sep 01, 2011 at 05:46:40PM -0400, Christoph Hellwig wrote:
> On Thu, Sep 01, 2011 at 02:22:15PM -0500, Alex Elder wrote:
> > that the buffer should be queued at unlock time, we now
> > just put it in the queue right away.  Seems reasonable.
> > Do you know why enqueueing it was delayed before?
> 
> I don't know why - it's a carryover from IRIX days,

Right. On Irix a buffer could simply have the BUF_DELWRI flag set on
it, and the buffer cache would take care of everything else. There
wasn't a specific delayed write list in Irix, instead there was a
fixed table of buffers (large!) that was scanned every 5 seconds
(20% scanned once per second) and the delwri buffers were gathered
by the scan.  Hence there were places in XFS where it simply set the
flag to mark a buffer delwri, and that's what this Linux code had to
catch.

> so long before my time.

The XFS code long predates me, too, but I spend a couple of years in
the trenches around the Irix buffer cache when I was at SGI so I at
least know why it was like that. ;)

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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