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Re: Device loses barrier support (was: Fixed patch for simple barriers.)

To: Andi Kleen <andi@xxxxxxxxxxxxxx>
Subject: Re: Device loses barrier support (was: Fixed patch for simple barriers.)
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 4 Dec 2008 12:53:07 -0500
Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>, Andi Kleen <andi-suse@xxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Alasdair G Kergon <agk@xxxxxxxxxx>, Milan Broz <mbroz@xxxxxxxxxx>
In-reply-to: <20081204174838.GS6703@xxxxxxxxxxxxxxxxxx>
References: <Pine.LNX.4.64.0812040009340.15169@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <20081204100050.GN6703@xxxxxxxxxxxxxxxxxx> <Pine.LNX.4.64.0812040836480.6118@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <20081204142015.GQ6703@xxxxxxxxxxxxxxxxxx> <Pine.LNX.4.64.0812040913510.6118@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <20081204145810.GR6703@xxxxxxxxxxxxxxxxxx> <Pine.LNX.4.64.0812041139200.2434@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <20081204174838.GS6703@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Thu, Dec 04, 2008 at 06:48:38PM +0100, Andi Kleen wrote:
> I think. Just the low level xfs_buf interface happens to use the asynchronous
> callbacks instead of calling into the block layer directly like jbd et.al.
> do.

Only delwri buffers are delayed in XFS, but the journaling code only
uses async buffers which *synchronously* call into the block layer, but
just don't wait for it to complete..

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