Messages in this thread | | | Date | Wed, 30 Oct 2019 18:53:02 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH] mm: vmscan: memcontrol: remove mem_cgroup_select_victim_node() |
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On Wed 30-10-19 13:44:55, Johannes Weiner wrote: > On Tue, Oct 29, 2019 at 04:47:53PM -0700, Shakeel Butt wrote: > > Since commit 1ba6fc9af35b ("mm: vmscan: do not share cgroup iteration > > between reclaimers"), the memcg reclaim does not bail out earlier based > > on sc->nr_reclaimed and will traverse all the nodes. All the reclaimable > > pages of the memcg on all the nodes will be scanned relative to the > > reclaim priority. So, there is no need to maintain state regarding which > > node to start the memcg reclaim from. Also KCSAN complains data races in > > the code maintaining the state. > > > > This patch effectively reverts the commit 889976dbcb12 ("memcg: reclaim > > memory from nodes in round-robin order") and the commit 453a9bf347f1 > > ("memcg: fix numa scan information update to be triggered by memory > > event"). > > > > Signed-off-by: Shakeel Butt <shakeelb@google.com> > > Reported-by: <syzbot+13f93c99c06988391efe@syzkaller.appspotmail.com> > > Excellent, thanks Shakeel! > Acked-by: Johannes Weiner <hannes@cmpxchg.org> > > Just a request on this bit: > > > @@ -3360,16 +3358,9 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, > > .may_unmap = 1, > > .may_swap = may_swap, > > }; > > + struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask); > > > > set_task_reclaim_state(current, &sc.reclaim_state); > > - /* > > - * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't > > - * take care of from where we get pages. So the node where we start the > > - * scan does not need to be the current node. > > - */ > > - nid = mem_cgroup_select_victim_node(memcg); > > - > > - zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK]; > > This works, but it *is* somewhat fragile if we decide to add bail-out > conditions to reclaim again. And some numa nodes receiving slightly > less pressure than others could be quite tricky to debug. > > Can we add a comment here that points out the assumption that the > zonelist walk is comprehensive, and that all nodes receive equal > reclaim pressure?
Makes sense
> Also, I think we should use sc.gfp_mask & ~__GFP_THISNODE, so that > allocations with a physical node preference still do node-agnostic > reclaim for the purpose of cgroup accounting.
Do not we exclude that by GFP_RECLAIM_MASK already?
-- Michal Hocko SUSE Labs
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