On Thu, Jan 15, 2015 at 03:48:38PM +0100, Michal Hocko wrote:
> On Thu 15-01-15 16:25:16, Vladimir Davydov wrote:
> > memcg = mem_cgroup_iter(root, NULL, &reclaim);
> > do {
> > [...]
> > if (memcg && is_classzone)
> > shrink_slab(sc->gfp_mask, zone_to_nid(zone),
> > memcg, sc->nr_scanned - scanned,
> > lru_pages);
> >
> > /*
> > * Direct reclaim and kswapd have to scan all memory
> > * cgroups to fulfill the overall scan target for the
> > * zone.
> > *
> > * Limit reclaim, on the other hand, only cares about
> > * nr_to_reclaim pages to be reclaimed and it will
> > * retry with decreasing priority if one round over the
> > * whole hierarchy is not sufficient.
> > */
> > if (!global_reclaim(sc) &&
> > sc->nr_reclaimed >= sc->nr_to_reclaim) {
> > mem_cgroup_iter_break(root, memcg);
> > break;
> > }
> > memcg = mem_cgroup_iter(root, memcg, &reclaim);
> > } while (memcg);
> >
> >
> > If we can ignore reclaimed slab pages here (?), let's drop this patch.
>
> I see what you are trying to achieve but can this lead to a serious
> over-reclaim?
I think it can, but only if we shrink an inode with lots of pages
attached to its address space (they also count to reclaim_state). In
this case, we overreclaim anyway though.
I agree that this is a high risk for a vague benefit. Let's drop it
until we see this problem in real life.
Thanks,
Vladimir
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