On Wed, May 28, 2014 at 02:10:23PM +0200, Michal Hocko wrote: > Hi Andrew, Johannes, > > On Mon 28-04-14 14:26:41, Michal Hocko wrote: > > This patchset introduces such low limit that is functionally similar > > to a minimum guarantee. Memcgs which are under their lowlimit are not > > considered eligible for the reclaim (both global and hardlimit) unless > > all groups under the reclaimed hierarchy are below the low limit when > > all of them are considered eligible. > > > > The previous version of the patchset posted as a RFC > > (http://marc.info/?l=linux-mm&m=138677140628677&w=2) suggested a > > hard guarantee without any fallback. More discussions led me to > > reconsidering the default behavior and come up a more relaxed one. The > > hard requirement can be added later based on a use case which really > > requires. It would be controlled by memory.reclaim_flags knob which > > would specify whether to OOM or fallback (default) when all groups are > > bellow low limit. > > It seems that we are not in a full agreement about the default behavior > yet. Johannes seems to be more for hard guarantee while I would like to > see the weaker approach first and move to the stronger model later. > Johannes, is this absolutely no-go for you? Do you think it is seriously > handicapping the semantic of the new knob? Well we certainly can't start OOMing where we previously didn't, that's called a regression and automatically limits our options. Any unexpected OOMs will be much more acceptable from a new feature than from configuration that previously "worked" and then stopped. > My main motivation for the weaker model is that it is hard to see all > the corner case right now and once we hit them I would like to see a > graceful fallback rather than fatal action like OOM killer. Besides that > the usaceses I am mostly interested in are OK with fallback when the > alternative would be OOM killer. I also feel that introducing a knob > with a weaker semantic which can be made stronger later is a sensible > way to go. We can't make it stronger, but we can make it weaker. Stronger is the simpler definition, it's simpler code, your usecases are fine with it, Greg and I prefer it too. I don't even know what we are arguing about here. Patch applies on top of mmots. --- >From ced6ac70bb274cdaa4c5d78b53420d84fb803dd7 Mon Sep 17 00:00:00 2001 From: Johannes Weiner <hannes@xxxxxxxxxxx> Date: Wed, 28 May 2014 09:37:05 -0400 Subject: [patch] mm: vmscan: treat memcg low limit as hard guarantee Don't hide low limit configuration problems behind weak semantics and quietly breach the set-up guarantees. Make it simple: memcg guarantees are equivalent to mlocked memory, anonymous memory without swap, kernel memory, pinned memory etc. - unreclaimable. If no memory can be reclaimed without otherwise breaching guarantees, it's a real problem, so let the machine OOM and dump the memory state in that situation. Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> --- include/linux/memcontrol.h | 5 ----- mm/memcontrol.c | 15 --------------- mm/vmscan.c | 41 +++++------------------------------------ 3 files changed, 5 insertions(+), 56 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index a5cf853129ec..c3a53cbb88eb 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -94,7 +94,6 @@ bool task_in_mem_cgroup(struct task_struct *task, extern bool mem_cgroup_within_guarantee(struct mem_cgroup *memcg, struct mem_cgroup *root); -extern bool mem_cgroup_all_within_guarantee(struct mem_cgroup *root); extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page); extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p); @@ -297,10 +296,6 @@ static inline bool mem_cgroup_within_guarantee(struct mem_cgroup *memcg, { return false; } -static inline bool mem_cgroup_all_within_guarantee(struct mem_cgroup *root) -{ - return false; -} static inline struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4df733e13727..85fdef53fcf1 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2788,7 +2788,6 @@ static struct mem_cgroup *mem_cgroup_lookup(unsigned short id) * * The given group is within its reclaim gurantee if it is below its low limit * or the same applies for any parent up the hierarchy until root (including). - * Such a group might be excluded from the reclaim. */ bool mem_cgroup_within_guarantee(struct mem_cgroup *memcg, struct mem_cgroup *root) @@ -2801,25 +2800,11 @@ bool mem_cgroup_within_guarantee(struct mem_cgroup *memcg, return true; if (memcg == root) break; - } while ((memcg = parent_mem_cgroup(memcg))); return false; } -bool mem_cgroup_all_within_guarantee(struct mem_cgroup *root) -{ - struct mem_cgroup *iter; - - for_each_mem_cgroup_tree(iter, root) - if (!mem_cgroup_within_guarantee(iter, root)) { - mem_cgroup_iter_break(root, iter); - return false; - } - - return true; -} - struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page) { struct mem_cgroup *memcg = NULL; diff --git a/mm/vmscan.c b/mm/vmscan.c index a8ffe4e616fe..c72493e8fb53 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2244,20 +2244,14 @@ static inline bool should_continue_reclaim(struct zone *zone, } /** - * __shrink_zone - shrinks a given zone + * shrink_zone - shrinks a given zone * * @zone: zone to shrink * @sc: scan control with additional reclaim parameters - * @honor_memcg_guarantee: do not reclaim memcgs which are within their memory - * guarantee - * - * Returns the number of reclaimed memcgs. */ -static unsigned __shrink_zone(struct zone *zone, struct scan_control *sc, - bool honor_memcg_guarantee) +static void shrink_zone(struct zone *zone, struct scan_control *sc) { unsigned long nr_reclaimed, nr_scanned; - unsigned nr_scanned_groups = 0; do { struct mem_cgroup *root = sc->target_mem_cgroup; @@ -2274,20 +2268,16 @@ static unsigned __shrink_zone(struct zone *zone, struct scan_control *sc, do { struct lruvec *lruvec; - /* Memcg might be protected from the reclaim */ - if (honor_memcg_guarantee && - mem_cgroup_within_guarantee(memcg, root)) { + /* Don't reclaim guaranteed memory */ + if (mem_cgroup_within_guarantee(memcg, root)) { /* - * It would be more optimal to skip the memcg - * subtree now but we do not have a memcg iter - * helper for that. Anyone? + * XXX: skip the entire subtree here */ memcg = mem_cgroup_iter(root, memcg, &reclaim); continue; } lruvec = mem_cgroup_zone_lruvec(zone, memcg); - nr_scanned_groups++; sc->swappiness = mem_cgroup_swappiness(memcg); shrink_lruvec(lruvec, sc); @@ -2316,27 +2306,6 @@ static unsigned __shrink_zone(struct zone *zone, struct scan_control *sc, } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed, sc->nr_scanned - nr_scanned, sc)); - - return nr_scanned_groups; -} - -static void shrink_zone(struct zone *zone, struct scan_control *sc) -{ - bool honor_guarantee = true; - - while (!__shrink_zone(zone, sc, honor_guarantee)) { - /* - * The previous round of reclaim didn't find anything to scan - * because - * a) the whole reclaimed hierarchy is within guarantee so - * we fallback to ignore the guarantee because other option - * would be the OOM - * b) multiple reclaimers are racing and so the first round - * should be retried - */ - if (mem_cgroup_all_within_guarantee(sc->target_mem_cgroup)) - honor_guarantee = false; - } } /* Returns true if compaction should go ahead for a high-order request */ -- 1.9.3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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