Messages in this thread | | | Date | Thu, 15 Jan 2015 16:25:16 +0300 | From | Vladimir Davydov <> | Subject | Re: [PATCH -mm v2] vmscan: move reclaim_state handling to shrink_slab |
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On Thu, Jan 15, 2015 at 01:58:20PM +0100, Michal Hocko wrote: > On Thu 15-01-15 11:37:53, Vladimir Davydov wrote: > > current->reclaim_state is only used to count the number of slab pages > > reclaimed by shrink_slab(). So instead of initializing it before we are > > > > Note that after this patch try_to_free_mem_cgroup_pages() will count not > > only reclaimed user pages, but also slab pages, which is expected, > > because it can reclaim kmem from kmem-active sub cgroups. > > Except that reclaim_state counts all freed slab objects that have > current->reclaim_state != NULL AFAIR. This includes also kfreed pages > from interrupt context and who knows what else and those pages might be > from a different memcgs, no?
Hmm, true, good point. Can an interrupt handler free a lot of memory though? Does RCU free objects from irq or soft irq context?
> Besides that I am not sure this makes any difference in the end. No > try_to_free_mem_cgroup_pages caller really cares about the exact > number of reclaimed pages. We care only about whether there was any > progress done - and even that not exactly (e.g. try_charge checks > mem_cgroup_margin before retry/oom so if sufficient kmem pages were > uncharged then we will notice that).
Frankly, I thought exactly the same initially, that's why I dropped reclaim_state handling from the initial memcg shrinkers patch set. However, then Hillf noticed that nr_reclaimed is checked right after calling shrink_slab() in the memcg iteration loop in shrink_zone():
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.
Thanks, Vladimir
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