Commit f3a53a3a authored by Tejun Heo's avatar Tejun Heo Committed by Linus Torvalds
Browse files

mm, memcontrol: implement memory.swap.events 

Add swap max and fail events so that userland can monitor and respond to
running out of swap.

I'm not too sure about the fail event.  Right now, it's a bit confusing
which stats / events are recursive and which aren't and also which ones
reflect events which originate from a given cgroup and which targets the
cgroup.  No idea what the right long term solution is and it could just
be that growing them organically is actually the only right thing to do.

Link: http://lkml.kernel.org/r/20180416231151.GI1911913@devbig577.frc2.facebook.com


Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: <linux-api@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent bb98f2c5

Documentation/admin-guide/cgroup-v2.rst

+16 −0
Original line number Diff line number Diff line
@@ -1199,6 +1199,22 @@ PAGE_SIZE multiple when read back. 
	Swap usage hard limit.  If a cgroup's swap usage reaches this

	limit, anonymous memory of the cgroup will not be swapped out.



  memory.swap.events

	A read-only flat-keyed file which exists on non-root cgroups.

	The following entries are defined.  Unless specified

	otherwise, a value change in this file generates a file

	modified event.



	  max

		The number of times the cgroup's swap usage was about

		to go over the max boundary and swap allocation

		failed.



	  fail

		The number of times swap allocation failed either

		because of running out of swap system-wide or max

		limit.





Usage Guidelines

~~~~~~~~~~~~~~~~

include/linux/memcontrol.h

+5 −0
Original line number Diff line number Diff line
@@ -53,6 +53,8 @@ enum memcg_memory_event { 
	MEMCG_HIGH,

	MEMCG_MAX,

	MEMCG_OOM,

	MEMCG_SWAP_MAX,

	MEMCG_SWAP_FAIL,

	MEMCG_NR_MEMORY_EVENTS,

};
@@ -208,6 +210,9 @@ struct mem_cgroup { 
	atomic_long_t memory_events[MEMCG_NR_MEMORY_EVENTS];

	struct cgroup_file events_file;



	/* handle for "memory.swap.events" */

	struct cgroup_file swap_events_file;



	/* protect arrays of thresholds */

	struct mutex thresholds_lock;

mm/memcontrol.c

+23 −1
Original line number Diff line number Diff line
@@ -6012,13 +6012,17 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry) 
	if (!memcg)

		return 0;



	if (!entry.val)

	if (!entry.val) {

		memcg_memory_event(memcg, MEMCG_SWAP_FAIL);

		return 0;

	}



	memcg = mem_cgroup_id_get_online(memcg);



	if (!mem_cgroup_is_root(memcg) &&

	    !page_counter_try_charge(&memcg->swap, nr_pages, &counter)) {

		memcg_memory_event(memcg, MEMCG_SWAP_MAX);

		memcg_memory_event(memcg, MEMCG_SWAP_FAIL);

		mem_cgroup_id_put(memcg);

		return -ENOMEM;

	}
@@ -6156,6 +6160,18 @@ static ssize_t swap_max_write(struct kernfs_open_file *of, 
	return nbytes;

}



static int swap_events_show(struct seq_file *m, void *v)

{

	struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));



	seq_printf(m, "max %lu\n",

		   atomic_long_read(&memcg->memory_events[MEMCG_SWAP_MAX]));

	seq_printf(m, "fail %lu\n",

		   atomic_long_read(&memcg->memory_events[MEMCG_SWAP_FAIL]));



	return 0;

}



static struct cftype swap_files[] = {

	{

		.name = "swap.current",
@@ -6168,6 +6184,12 @@ static struct cftype swap_files[] = { 
		.seq_show = swap_max_show,

		.write = swap_max_write,

	},

	{

		.name = "swap.events",

		.flags = CFTYPE_NOT_ON_ROOT,

		.file_offset = offsetof(struct mem_cgroup, swap_events_file),

		.seq_show = swap_events_show,

	},

	{ }	/* terminate */

};

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