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



On Mon, Jan 13 2014 at  6:45pm -0500,
Mikulas Patocka <mpatocka redhat com> wrote:

> 
> 
> 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.

How about move the conditional inside the do { } ?

I really dislike the style you've used on this, is there anywhere else
in the kernel that does this?


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