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

[Chris Down <chris@chrisdown.name>]

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