mm: memcontrol: don't count limit-setting reclaim as memory pressure (e22c6ed9) · Commits · 戴 / test

When an outside process lowers one of the memory limits of a cgroup (or uses the force_empty knob in cgroup1), direct reclaim is performed in the context of the write(), in order to directly enforce the new limit and have it being met by the time the write() returns. Currently, this reclaim activity is accounted as memory pressure in the cgroup that the writer(!) belongs to. This is unexpected. It specifically causes problems for senpai (https://github.com/facebookincubator/senpai ), which is an agent that routinely adjusts the memory limits and performs associated reclaim work in tens or even hundreds of cgroups running on the host. The cgroup that senpai is running in itself will report elevated levels of memory pressure, even though it itself is under no memory shortage or any sort of distress. Move the psi annotation from the central cgroup reclaim function to callsites in the allocation context, and thereby no longer count any limit-setting reclaim as memory pressure. If the newly set limit causes the workload inside the cgroup into direct reclaim, that of course will continue to count as memory pressure. Signed-off-by:

Johannes Weiner <hannes@cmpxchg.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Reviewed-by:

Shakeel Butt <shakeelb@google.com> Reviewed-by:

Roman Gushchin <guro@fb.com> Acked-by:

Chris Down <chris@chrisdown.name> Acked-by:

Michal Hocko <mhocko@suse.com> Link: http://lkml.kernel.org/r/20200728135210.379885-2-hannes@cmpxchg.org Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -2374,12 +2374,18 @@ static unsigned long reclaim_high(struct mem_cgroup *memcg,
		unsigned long nr_reclaimed = 0;

		do {
		unsigned long pflags;

		if (page_counter_read(&memcg->memory) <=
		READ_ONCE(memcg->memory.high))
		continue;

		memcg_memory_event(memcg, MEMCG_HIGH);

		psi_memstall_enter(&pflags);
		nr_reclaimed += try_to_free_mem_cgroup_pages(memcg, nr_pages,
		gfp_mask, true);
		psi_memstall_leave(&pflags);
		} while ((memcg = parent_mem_cgroup(memcg)) &&
		!mem_cgroup_is_root(memcg));

		@@ -2621,10 +2627,11 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
		int nr_retries = MAX_RECLAIM_RETRIES;
		struct mem_cgroup *mem_over_limit;
		struct page_counter *counter;
		enum oom_status oom_status;
		unsigned long nr_reclaimed;
		bool may_swap = true;
		bool drained = false;
		enum oom_status oom_status;
		unsigned long pflags;

		if (mem_cgroup_is_root(memcg))
		return 0;
		@@ -2684,8 +2691,10 @@ retry:

		memcg_memory_event(mem_over_limit, MEMCG_MAX);

		psi_memstall_enter(&pflags);
		nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,
		gfp_mask, may_swap);
		psi_memstall_leave(&pflags);

		if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
		goto retry;

mm/vmscan.c

+0 −6

Original line number	Diff line number	Diff line
		@@ -3310,7 +3310,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
		bool may_swap)
		{
		unsigned long nr_reclaimed;
		unsigned long pflags;
		unsigned int noreclaim_flag;
		struct scan_control sc = {
		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
		@@ -3331,17 +3330,12 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
		struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);

		set_task_reclaim_state(current, &sc.reclaim_state);

		trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);

		psi_memstall_enter(&pflags);
		noreclaim_flag = memalloc_noreclaim_save();

		nr_reclaimed = do_try_to_free_pages(zonelist, &sc);

		memalloc_noreclaim_restore(noreclaim_flag);
		psi_memstall_leave(&pflags);

		trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
		set_task_reclaim_state(current, NULL);

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