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
