Re: [patch 3/3]vmscan: cleanup kswapd_try_to_sleep

[Shaohua Li <shaohua.li@intel.com>]

On Fri, Jul 29, 2011 at 05:39:29PM +0800, Minchan Kim wrote:
> On Thu, Jul 28, 2011 at 04:13:09PM +0800, Shaohua Li wrote:
> > cleanup kswapd_try_to_sleep() a little bit. Sometimes kswapd doesn't
> > really sleep. In such case, don't call prepare_to_wait/finish_wait.
> > It just wastes CPU.
> > 
> > Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> 
> And it increases just code size a little bit even without big benefit of CPU.
> You said it's cleanup but I doubt how it helps readability.
> So code itself dosn't have a problem but I don't like it.
> 
> barrios@barrios-desktop:~/linux-mmotm$ size mm/vmscan.o.old
>    text	   data	    bss	    dec	    hex	filename
>   10271	     30	      8	  10309	   2845	mm/vmscan.o.old
> barrios@barrios-desktop:~/linux-mmotm$ size mm/vmscan.o
>    text	   data	    bss	    dec	    hex	filename
>   10287	     30	      8	  10325	   2855	mm/vmscan.o
I'm curious why the size is increased, the patch doesn't add new code.
Maybe gcc has different optimization.
This hasn't big benefit for sure, but both prepare_to_wait/finish_wait
use spinlock, it's expensive operation even without contention. From
this point view, it has benefit because we don't blindly call them.
But anyway, it's a trival patch. I'm fine if it's rejected.

Thanks,
Shaohua

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