[Sheepdog] [PATCH] sheep: unify create_and_write logic for cow and regular object

[tao.peng at emc.com]

> -----Original Message-----
> From: sheepdog-bounces at lists.wpkg.org
> [mailto:sheepdog-bounces at lists.wpkg.org] On Behalf Of Christoph Hellwig
> Sent: Tuesday, November 15, 2011 4:22 PM
> To: Liu Yuan
> Cc: Christoph Hellwig; sheepdog at lists.wpkg.org
> Subject: Re: [Sheepdog] [PATCH] sheep: unify create_and_write logic for cow and
> regular object
> 
> On Tue, Nov 15, 2011 at 04:18:52PM +0800, Liu Yuan wrote:
> > Umm, seems useless, I just squeeze it to the code path. any noticeable
> > performance penalty?
> 
> With the current O_SYNC I/O model it at least means an additional log
> force, which on disks will be very noticeable.  So unless you really
> see a difference in I/O patterns don't do it.
Just out of curiosity, won't fallocate() be a better hint to underlying file system which can then create a better on disk layout? With O_SYNC IO it forces allocation on each write...

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