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Re: [PATCH] xfs: preallocation transactions do not need to be synchronou

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: preallocation transactions do not need to be synchronous
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 10 Mar 2011 02:36:34 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1299713852-7663-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1299713852-7663-1-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Mar 10, 2011 at 10:37:32AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> Preallocation and hole punch transactions are currently synchronous
> and this is causing performance problems in some cases. The
> transactions don't need to be synchronous as we don't need to
> guarantee the preallocation is persistent on disk until a
> fdatasync, fsync, sync operation occurs. If the file is opened
> O_SYNC or O_DATASYNC, only then should the transaction be issued
> synchronously.

I had the same patch in my queue, but it turns out even that isn't
enough for good performance when used fallocate in the fast path (e.g.
recent Samba).  I'll send a more comprehensive optimization that
includes this soon.

I also refactored the whole area to make the various flags more
sensible.

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