Date:	Sun, 13 Jan 2013 02:50:23 -0600
From:	Simon Jeons <simon.jeons@...il.com>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Mel Gorman <mgorman@...e.de>,
	Glauber Costa <glommer@...allels.com>,
	Michal Hocko <mhocko@...e.cz>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Thelen <gthelen@...gle.com>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	John Stultz <john.stultz@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, kernel-team@...roid.com
Subject: Re: [PATCH 1/2] Add mempressure cgroup

On Fri, 2013-01-04 at 00:29 -0800, Anton Vorontsov wrote:
> This commit implements David Rientjes' idea of mempressure cgroup.
> 
> The main characteristics are the same to what I've tried to add to vmevent
> API; internally, it uses Mel Gorman's idea of scanned/reclaimed ratio for
> pressure index calculation. But we don't expose the index to the userland.
> Instead, there are three levels of the pressure:
> 
>  o low (just reclaiming, e.g. caches are draining);
>  o medium (allocation cost becomes high, e.g. swapping);
>  o oom (about to oom very soon).
> 
> The rationale behind exposing levels and not the raw pressure index
> described here: http://lkml.org/lkml/2012/11/16/675
> 
> For a task it is possible to be in both cpusets, memcg and mempressure
> cgroups, so by rearranging the tasks it is possible to watch a specific
> pressure (i.e. caused by cpuset and/or memcg).
> 
> Note that while this adds the cgroups support, the code is well separated
> and eventually we might add a lightweight, non-cgroups API, i.e. vmevent.
> But this is another story.
> 
> Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.org>
> ---
>  Documentation/cgroups/mempressure.txt |  50 ++++++
>  include/linux/cgroup_subsys.h         |   6 +
>  include/linux/vmstat.h                |  11 ++
>  init/Kconfig                          |  12 ++
>  mm/Makefile                           |   1 +
>  mm/mempressure.c                      | 330 ++++++++++++++++++++++++++++++++++
>  mm/vmscan.c                           |   4 +
>  7 files changed, 414 insertions(+)
>  create mode 100644 Documentation/cgroups/mempressure.txt
>  create mode 100644 mm/mempressure.c
> 
> diff --git a/Documentation/cgroups/mempressure.txt b/Documentation/cgroups/mempressure.txt
> new file mode 100644
> index 0000000..dbc0aca
> --- /dev/null
> +++ b/Documentation/cgroups/mempressure.txt
> @@ -0,0 +1,50 @@
> +  Memory pressure cgroup
> +~~~~~~~~~~~~~~~~~~~~~~~~~~
> +  Before using the mempressure cgroup, make sure you have it mounted:
> +
> +   # cd /sys/fs/cgroup/
> +   # mkdir mempressure
> +   # mount -t cgroup cgroup ./mempressure -o mempressure
> +
> +  It is possible to combine cgroups, for example you can mount memory
> +  (memcg) and mempressure cgroups together:
> +
> +   # mount -t cgroup cgroup ./mempressure -o memory,mempressure
> +
> +  That way the reported pressure will honour memory cgroup limits. The
> +  same goes for cpusets.
> +
> +  After the hierarchy is mounted, you can use the following API:
> +
> +  /sys/fs/cgroup/.../mempressure.level
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +  To maintain the interactivity/memory allocation cost, one can use the
> +  pressure level notifications, and the levels are defined like this:
> +
> +  The "low" level means that the system is reclaiming memory for new
> +  allocations. Monitoring reclaiming activity might be useful for
> +  maintaining overall system's cache level. Upon notification, the program
> +  (typically "Activity Manager") might analyze vmstat and act in advance
> +  (i.e. prematurely shutdown unimportant services).
> +
> +  The "medium" level means that the system is experiencing medium memory
> +  pressure, there is some mild swapping activity. Upon this event
> +  applications may decide to free any resources that can be easily
> +  reconstructed or re-read from a disk.
> +
> +  The "oom" level means that the system is actively thrashing, it is about
> +  to out of memory (OOM) or even the in-kernel OOM killer is on its way to
> +  trigger. Applications should do whatever they can to help the system.
> +
> +  Event control:
> +    Is used to setup an eventfd with a level threshold. The argument to
> +    the event control specifies the level threshold.
> +  Read:
> +    Reads mempory presure levels: low, medium or oom.
> +  Write:
> +    Not implemented.
> +  Test:
> +    To set up a notification:
> +
> +    # cgroup_event_listener ./mempressure.level low
> +    ("low", "medium", "oom" are permitted.)
> diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
> index f204a7a..b9802e2 100644
> --- a/include/linux/cgroup_subsys.h
> +++ b/include/linux/cgroup_subsys.h
> @@ -37,6 +37,12 @@ SUBSYS(mem_cgroup)
>  
>  /* */
>  
> +#if IS_SUBSYS_ENABLED(CONFIG_CGROUP_MEMPRESSURE)
> +SUBSYS(mpc_cgroup)
> +#endif
> +
> +/* */
> +
>  #if IS_SUBSYS_ENABLED(CONFIG_CGROUP_DEVICE)
>  SUBSYS(devices)
>  #endif
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index a13291f..c1a66c7 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -10,6 +10,17 @@
>  
>  extern int sysctl_stat_interval;
>  
> +struct mem_cgroup;
> +#ifdef CONFIG_CGROUP_MEMPRESSURE
> +extern void vmpressure(struct mem_cgroup *memcg,
> +		       ulong scanned, ulong reclaimed);
> +extern void vmpressure_prio(struct mem_cgroup *memcg, int prio);
> +#else
> +static inline void vmpressure(struct mem_cgroup *memcg,
> +			      ulong scanned, ulong reclaimed) {}
> +static inline void vmpressure_prio(struct mem_cgroup *memcg, int prio) {}
> +#endif
> +
>  #ifdef CONFIG_VM_EVENT_COUNTERS
>  /*
>   * Light weight per cpu counter implementation.
> diff --git a/init/Kconfig b/init/Kconfig
> index 7d30240..d526249 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -891,6 +891,18 @@ config MEMCG_KMEM
>  	  the kmem extension can use it to guarantee that no group of processes
>  	  will ever exhaust kernel resources alone.
>  
> +config CGROUP_MEMPRESSURE
> +	bool "Memory pressure monitor for Control Groups"
> +	help
> +	  The memory pressure monitor cgroup provides a facility for
> +	  userland programs so that they could easily assist the kernel
> +	  with the memory management. So far the API provides simple,
> +	  levels-based memory pressure notifications.
> +
> +	  For more information see Documentation/cgroups/mempressure.txt
> +
> +	  If unsure, say N.
> +
>  config CGROUP_HUGETLB
>  	bool "HugeTLB Resource Controller for Control Groups"
>  	depends on RESOURCE_COUNTERS && HUGETLB_PAGE && EXPERIMENTAL
> diff --git a/mm/Makefile b/mm/Makefile
> index 3a46287..e69bbda 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -51,6 +51,7 @@ obj-$(CONFIG_MIGRATION) += migrate.o
>  obj-$(CONFIG_QUICKLIST) += quicklist.o
>  obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o
>  obj-$(CONFIG_MEMCG) += memcontrol.o page_cgroup.o
> +obj-$(CONFIG_CGROUP_MEMPRESSURE) += mempressure.o
>  obj-$(CONFIG_CGROUP_HUGETLB) += hugetlb_cgroup.o
>  obj-$(CONFIG_MEMORY_FAILURE) += memory-failure.o
>  obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
> diff --git a/mm/mempressure.c b/mm/mempressure.c
> new file mode 100644
> index 0000000..ea312bb
> --- /dev/null
> +++ b/mm/mempressure.c
> @@ -0,0 +1,330 @@
> +/*
> + * Linux VM pressure
> + *
> + * Copyright 2012 Linaro Ltd.
> + *		  Anton Vorontsov <anton.vorontsov@...aro.org>
> + *
> + * Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro,
> + * Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published
> + * by the Free Software Foundation.
> + */
> +
> +#include <linux/cgroup.h>
> +#include <linux/fs.h>
> +#include <linux/sched.h>
> +#include <linux/mm.h>
> +#include <linux/vmstat.h>
> +#include <linux/eventfd.h>
> +#include <linux/swap.h>
> +#include <linux/printk.h>
> +
> +static void mpc_vmpressure(struct mem_cgroup *memcg, ulong s, ulong r);
> +
> +/*
> + * Generic VM Pressure routines (no cgroups or any other API details)
> + */
> +
> +/*
> + * The window size is the number of scanned pages before we try to analyze
> + * the scanned/reclaimed ratio (or difference).
> + *
> + * It is used as a rate-limit tunable for the "low" level notification,
> + * and for averaging medium/oom levels. Using small window sizes can cause
> + * lot of false positives, but too big window size will delay the
> + * notifications.
> + */
> +static const uint vmpressure_win = SWAP_CLUSTER_MAX * 16;
> +static const uint vmpressure_level_med = 60;
> +static const uint vmpressure_level_oom = 99;
> +static const uint vmpressure_level_oom_prio = 4;
> +
> +enum vmpressure_levels {
> +	VMPRESSURE_LOW = 0,
> +	VMPRESSURE_MEDIUM,
> +	VMPRESSURE_OOM,
> +	VMPRESSURE_NUM_LEVELS,
> +};
> +
> +static const char *vmpressure_str_levels[] = {
> +	[VMPRESSURE_LOW] = "low",
> +	[VMPRESSURE_MEDIUM] = "medium",
> +	[VMPRESSURE_OOM] = "oom",
> +};
> +
> +static enum vmpressure_levels vmpressure_level(uint pressure)
> +{
> +	if (pressure >= vmpressure_level_oom)
> +		return VMPRESSURE_OOM;
> +	else if (pressure >= vmpressure_level_med)
> +		return VMPRESSURE_MEDIUM;
> +	return VMPRESSURE_LOW;
> +}
> +
> +static ulong vmpressure_calc_level(uint win, uint s, uint r)
> +{
> +	ulong p;
> +
> +	if (!s)
> +		return 0;
> +
> +	/*
> +	 * We calculate the ratio (in percents) of how many pages were
> +	 * scanned vs. reclaimed in a given time frame (window). Note that
> +	 * time is in VM reclaimer's "ticks", i.e. number of pages
> +	 * scanned. This makes it possible to set desired reaction time
> +	 * and serves as a ratelimit.
> +	 */
> +	p = win - (r * win / s);
> +	p = p * 100 / win;
> +
> +	pr_debug("%s: %3lu  (s: %6u  r: %6u)\n", __func__, p, s, r);
> +
> +	return vmpressure_level(p);
> +}
> +
> +void vmpressure(struct mem_cgroup *memcg, ulong scanned, ulong reclaimed)
> +{
> +	if (!scanned)
> +		return;
> +	mpc_vmpressure(memcg, scanned, reclaimed);
> +}
> +
> +void vmpressure_prio(struct mem_cgroup *memcg, int prio)
> +{
> +	if (prio > vmpressure_level_oom_prio)
> +		return;
> +
> +	/* OK, the prio is below the threshold, send the pre-OOM event. */
> +	vmpressure(memcg, vmpressure_win, 0);
> +}
> +
> +/*
> + * Memory pressure cgroup code
> + */
> +
> +struct mpc_event {
> +	struct eventfd_ctx *efd;
> +	enum vmpressure_levels level;
> +	struct list_head node;
> +};
> +
> +struct mpc_state {
> +	struct cgroup_subsys_state css;
> +
> +	uint scanned;
> +	uint reclaimed;
> +	struct mutex sr_lock;
> +
> +	struct list_head events;
> +	struct mutex events_lock;
> +
> +	struct work_struct work;
> +};
> +
> +static struct mpc_state *wk2mpc(struct work_struct *wk)
> +{
> +	return container_of(wk, struct mpc_state, work);
> +}
> +
> +static struct mpc_state *css2mpc(struct cgroup_subsys_state *css)
> +{
> +	return container_of(css, struct mpc_state, css);
> +}
> +
> +static struct mpc_state *tsk2mpc(struct task_struct *tsk)
> +{
> +	return css2mpc(task_subsys_state(tsk, mpc_cgroup_subsys_id));
> +}
> +
> +static struct mpc_state *cg2mpc(struct cgroup *cg)
> +{
> +	return css2mpc(cgroup_subsys_state(cg, mpc_cgroup_subsys_id));
> +}
> +
> +static void mpc_event(struct mpc_state *mpc, ulong s, ulong r)
> +{
> +	struct mpc_event *ev;
> +	int level = vmpressure_calc_level(vmpressure_win, s, r);
> +
> +	mutex_lock(&mpc->events_lock);
> +
> +	list_for_each_entry(ev, &mpc->events, node) {
> +		if (level >= ev->level)
> +			eventfd_signal(ev->efd, 1);
> +	}
> +
> +	mutex_unlock(&mpc->events_lock);
> +}
> +
> +static void mpc_vmpressure_wk_fn(struct work_struct *wk)
> +{
> +	struct mpc_state *mpc = wk2mpc(wk);
> +	ulong s;
> +	ulong r;
> +
> +	mutex_lock(&mpc->sr_lock);
> +	s = mpc->scanned;
> +	r = mpc->reclaimed;
> +	mpc->scanned = 0;
> +	mpc->reclaimed = 0;
> +	mutex_unlock(&mpc->sr_lock);
> +
> +	mpc_event(mpc, s, r);
> +}
> +
> +static void __mpc_vmpressure(struct mpc_state *mpc, ulong s, ulong r)
> +{
> +	mutex_lock(&mpc->sr_lock);
> +	mpc->scanned += s;
> +	mpc->reclaimed += r;
> +	mutex_unlock(&mpc->sr_lock);
> +
> +	if (s < vmpressure_win || work_pending(&mpc->work))
> +		return;
> +
> +	schedule_work(&mpc->work);
> +}
> +
> +static void mpc_vmpressure(struct mem_cgroup *memcg, ulong s, ulong r)
> +{
> +	/*
> +	 * There are two options for implementing cgroup pressure
> +	 * notifications:
> +	 *
> +	 * - Store pressure counter atomically in the task struct. Upon
> +	 *   hitting 'window' wake up a workqueue that will walk every
> +	 *   task and sum per-thread pressure into cgroup pressure (to
> +	 *   which the task belongs). The cons are obvious: bloats task
> +	 *   struct, have to walk all processes and makes pressue less
> +	 *   accurate (the window becomes per-thread);
> +	 *
> +	 * - Store pressure counters in per-cgroup state. This is easy and
> +	 *   straightforward, and that's how we do things here. But this
> +	 *   requires us to not put the vmpressure hooks into hotpath,
> +	 *   since we have to grab some locks.
> +	 */
> +
> +#ifdef CONFIG_MEMCG
> +	if (memcg) {
> +		struct cgroup_subsys_state *css = mem_cgroup_css(memcg);
> +		struct cgroup *cg = css->cgroup;
> +		struct mpc_state *mpc = cg2mpc(cg);
> +
> +		if (mpc)
> +			__mpc_vmpressure(mpc, s, r);
> +		return;
> +	}
> +#endif
> +	task_lock(current);
> +	__mpc_vmpressure(tsk2mpc(current), s, r);
> +	task_unlock(current);
> +}
> +
> +static struct cgroup_subsys_state *mpc_css_alloc(struct cgroup *cg)
> +{
> +	struct mpc_state *mpc;
> +
> +	mpc = kzalloc(sizeof(*mpc), GFP_KERNEL);
> +	if (!mpc)
> +		return ERR_PTR(-ENOMEM);
> +
> +	mutex_init(&mpc->sr_lock);
> +	mutex_init(&mpc->events_lock);
> +	INIT_LIST_HEAD(&mpc->events);
> +	INIT_WORK(&mpc->work, mpc_vmpressure_wk_fn);
> +
> +	return &mpc->css;
> +}
> +
> +static void mpc_css_free(struct cgroup *cg)
> +{
> +	struct mpc_state *mpc = cg2mpc(cg);
> +
> +	kfree(mpc);
> +}
> +
> +static ssize_t mpc_read_level(struct cgroup *cg, struct cftype *cft,
> +			      struct file *file, char __user *buf,
> +			      size_t sz, loff_t *ppos)
> +{
> +	struct mpc_state *mpc = cg2mpc(cg);
> +	uint level;
> +	const char *str;
> +
> +	mutex_lock(&mpc->sr_lock);
> +
> +	level = vmpressure_calc_level(vmpressure_win,
> +			mpc->scanned, mpc->reclaimed);
> +
> +	mutex_unlock(&mpc->sr_lock);
> +
> +	str = vmpressure_str_levels[level];
> +	return simple_read_from_buffer(buf, sz, ppos, str, strlen(str));
> +}
> +
> +static int mpc_register_level(struct cgroup *cg, struct cftype *cft,
> +			      struct eventfd_ctx *eventfd, const char *args)
> +{
> +	struct mpc_state *mpc = cg2mpc(cg);
> +	struct mpc_event *ev;
> +	int lvl;
> +
> +	for (lvl = 0; lvl < VMPRESSURE_NUM_LEVELS; lvl++) {
> +		if (!strcmp(vmpressure_str_levels[lvl], args))
> +			break;
> +	}
> +
> +	if (lvl >= VMPRESSURE_NUM_LEVELS)
> +		return -EINVAL;
> +
> +	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
> +	if (!ev)
> +		return -ENOMEM;
> +
> +	ev->efd = eventfd;
> +	ev->level = lvl;
> +
> +	mutex_lock(&mpc->events_lock);
> +	list_add(&ev->node, &mpc->events);
> +	mutex_unlock(&mpc->events_lock);
> +
> +	return 0;
> +}
> +
> +static void mpc_unregister_level(struct cgroup *cg, struct cftype *cft,
> +				 struct eventfd_ctx *eventfd)
> +{
> +	struct mpc_state *mpc = cg2mpc(cg);
> +	struct mpc_event *ev;
> +
> +	mutex_lock(&mpc->events_lock);
> +	list_for_each_entry(ev, &mpc->events, node) {
> +		if (ev->efd != eventfd)
> +			continue;
> +		list_del(&ev->node);
> +		kfree(ev);
> +		break;
> +	}
> +	mutex_unlock(&mpc->events_lock);
> +}
> +
> +static struct cftype mpc_files[] = {
> +	{
> +		.name = "level",
> +		.read = mpc_read_level,
> +		.register_event = mpc_register_level,
> +		.unregister_event = mpc_unregister_level,
> +	},
> +	{},
> +};
> +
> +struct cgroup_subsys mpc_cgroup_subsys = {
> +	.name = "mempressure",
> +	.subsys_id = mpc_cgroup_subsys_id,
> +	.css_alloc = mpc_css_alloc,
> +	.css_free = mpc_css_free,
> +	.base_cftypes = mpc_files,
> +};
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 16b42af..fed0e04 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1900,6 +1900,9 @@ restart:
>  		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
>  				   sc, LRU_ACTIVE_ANON);
>  
> +	vmpressure(sc->target_mem_cgroup,
> +		   sc->nr_scanned - nr_scanned, nr_reclaimed);
> +
>  	/* reclaim/compaction might need reclaim to continue */
>  	if (should_continue_reclaim(lruvec, nr_reclaimed,
>  				    sc->nr_scanned - nr_scanned, sc))
> @@ -2122,6 +2125,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  		count_vm_event(ALLOCSTALL);
>  
>  	do {
> +		vmpressure_prio(sc->target_mem_cgroup, sc->priority);

Why need function vmpressure_prio? It seems that it's reduncated.  

>  		sc->nr_scanned = 0;
>  		aborted_reclaim = shrink_zones(zonelist, sc);
>  


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