Re: [PATCH v2 02/28] vmscan: take at least one pass with shrinkers

[Ric Mason <ric.masonn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Glauber,
On 04/01/2013 04:10 PM, Glauber Costa wrote:
> Hi Kame,
>
>> Doesn't this break
>>
>> ==
>>                 /*
>>                  * copy the current shrinker scan count into a local variable
>>                  * and zero it so that other concurrent shrinker invocations
>>                  * don't also do this scanning work.
>>                  */
>>                 nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
>> ==
>>
>> This xchg magic ?
>>
>> Thnks,
>> -Kame
> This is done before the actual reclaim attempt, and all it does is to
> indicate to other concurrent shrinkers that "I've got it", and others
> should not attempt to shrink.
>
> Even before I touch this, this quantity represents the number of
> entities we will try to shrink. Not necessarily we will succeed. What my
> patch does, is to try at least once if the number is too small.
>
> Before it, we will try to shrink 512 objects and succeed at 0 (because
> batch is 1024). After this, we will try to free 512 objects and succeed
> at an undefined quantity between 0 and 512.

Where you get the magic number 512 and 1024? The value of SHRINK_BATCH
is 128.

>
> In both cases, we will zero out nr_in_batch in the shrinker structure to
> notify other shrinkers that we are the ones shrinking.
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo-Bw31MaZKKs0EbZ0PF+XxCw@public.gmane.org  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org"> email-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org </a>