Re: [PATCH REBASED] mm, memcg: Make scan aggression always exclude protection

[Chris Down]

Roman Gushchin writes:
> I've noticed that the old version is just wrong: if cgroup_size is way smaller
> than max(min, low), scan will be set to -lruvec_size.
> Given that it's unsigned long, we'll end up with scanning the whole list
> (due to clamp() below).

Are you certain? If so, I don't see what you mean. This is how the code looks 
in Linus' tree after the fixups:

   unsigned long cgroup_size = mem_cgroup_size(memcg);
   unsigned long baseline = 0;

   if (!sc->memcg_low_reclaim)
           baseline = lruvec_size;
   scan = lruvec_size * cgroup_size / protection - baseline;

This works correctly as far as I can tell:

low reclaim case:

   In [1]: cgroup_size=50; lruvec_size=10; protection=2000; baseline=0; lruvec_size * cgroup_size // protection - baseline
   Out[1]: 0

normal case:

   In [2]: cgroup_size=3000; lruvec_size=10; protection=2000; baseline=lruvec_size; lruvec_size * cgroup_size // protection - baseline
   Out[2]: 5