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

[Liu Yuan]

On 11/15/2011 04:21 PM, Christoph Hellwig wrote:

> 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.
> 


After a second thought, if we use DIO later, so this might not stand. In
ext4, fallocate() will modify the metadata and write a journal
transaction, but it may not be committed to the disk immediately. Also
as Tao has mentioned in another mail, with larger block size, we should
benefit from it.

Thanks,
Yuan