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Re: [dm-devel] [PATCH v2 7/7] dm snapshot: use bufio prefetch




On Mon, 13 Jan 2014, Mike Snitzer wrote:

> On Mon, Jan 13 2014 at  5:00pm -0500,
> Mikulas Patocka <mpatocka redhat com> wrote:
> 
> > No.
> > 
> > This changed patch inefficiently loops in bufio_prefetch_chunks for each 
> > buffer that is read.
> 
> Yeah, I overlooked the importance of preserving prefetch_area (which
> explains the unlikely you had).  But my intent was to make your code
> less "special"; your if (DM_PREFETCH_CHUNKS) do { } while() code to
> avoid the extra indentation is pretty ugly.
> 
> Given your current code, DM_PREFETCH_CHUNKS is always 12 so why not just
> remove the check?

If someone ever changes it to a variable, the condition is there avoid 
unneeded call to dm_bufio_prefetch. The compiler optimizes out the 
constant expression, so it doesn't matter that it's there.

Mikulas


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