Re: [RFC v2] Add mempressure cgroup

[Kirill A. Shutemov]

On Mon, Dec 10, 2012 at 01:58:38AM -0800, Anton Vorontsov wrote:

CC: linux-api@

> The main changes for the mempressure cgroup:
> 
> - Added documentation, describes APIs and the purpose;
> 
> - Implemented shrinker interface, this is based on Andrew's idea and
>   supersedes my "balance" level idea;
> 
> - The shrinker interface comes with a stress-test utility, that is what
>   Andrew was also asking for. A simple app that we can run and see if the
>   thing works as expected;
> 
> - Added reclaimer's target_mem_cgroup handling;
> 
> - As promised, added support for multiple listeners, and fixed some other
>   comments on the previous RFC.
> 
> Just for the reference, the first mempressure RFC:
> 
>   http://lkml.org/lkml/2012/11/28/109
> 
> Signed-off-by: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
> ---
>  Documentation/cgroups/mempressure.txt    |  89 ++++++
>  Documentation/cgroups/mempressure_test.c | 209 +++++++++++++
>  include/linux/cgroup_subsys.h            |   6 +
>  include/linux/vmstat.h                   |  11 +
>  init/Kconfig                             |  12 +
>  mm/Makefile                              |   1 +
>  mm/mempressure.c                         | 488 +++++++++++++++++++++++++++++++
>  mm/vmscan.c                              |   4 +
>  8 files changed, 820 insertions(+)
>  create mode 100644 Documentation/cgroups/mempressure.txt
>  create mode 100644 Documentation/cgroups/mempressure_test.c
>  create mode 100644 mm/mempressure.c
> 
> diff --git a/Documentation/cgroups/mempressure.txt b/Documentation/cgroups/mempressure.txt
> new file mode 100644
> index 0000000..913accc
> --- /dev/null
> +++ b/Documentation/cgroups/mempressure.txt
> @@ -0,0 +1,89 @@
> +  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
> +
> +  After that, you can use the following files:
> +
> +  /sys/fs/cgroup/.../mempressure.shrinker
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +  The file implements userland shrinker (memory reclaimer) interface, so
> +  that the kernel can ask userland to help with the memory reclaiming
> +  process.
> +
> +  There are two basic concepts: chunks and chunks' size. The program must
> +  tell the kernel the granularity of its allocations (chunk size) and the
> +  number of reclaimable chunks. The granularity may be not 100% accurate,
> +  but the more it is accurate, the better. I.e. suppose the application
> +  has 200 page renders cached (but not displayed), 1MB each. So the chunk
> +  size is 1MB, and the number of chunks is 200.
> +
> +  The granularity is specified during shrinker registration (i.e. via
> +  argument to the event_control cgroup file; and it is OK to register
> +  multiple shrinkers for different granularities). The number of
> +  reclaimable chunks is specified by writing to the mempressure.shrinker
> +  file.
> +
> +  The notification comes through the eventfd() interface. Upon the
> +  notification, a read() from the eventfd returns the number of chunks to
> +  reclaim (free).
> +
> +  It is assumed that the application will free the specified amount of
> +  chunks before reading from the eventfd again. If that is not the case,
> +  suppose the program was not able to reclaim the chunks, then application
> +  should re-add the amount of chunks by writing to the
> +  mempressure.shrinker file (otherwise the chunks won't be accounted by
> +  the kernel, since it assumes that they were reclaimed).
> +
> +  Event control:
> +    Used to setup shrinker events. There is only one argument for the
> +    event control: chunk size in bytes.
> +  Read:
> +    Not implemented.
> +  Write:
> +    Writes must be in "<eventfd> <number of chunks>" format. Positive
> +    numbers increment the internal counter, negative numbers decrement it
> +    (but the kernel prevents the counter from falling down below zero).
> +  Test:
> +    See mempressure_test.c

I think the interface is broken. One eventfd can be registered to get
many different notifications.

The only information you have on POLLIN/read() is "something happened".
Then, it's up to userspace to find out what had happened: if it's memory
pressure or cgroup is removed or whatever else.

One more point: unlike kernel side shrinkers, userspace shrinkers cannot
be synchronous. I doubt they can be useful in real world situations.

I personally feel that mempressure.level interface is enough.

> +  /sys/fs/cgroup/.../mempressure.level
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +  Instead of working on the bytes level (like shrinkers), one may decide
> +  to maintain the interactivity/memory allocation cost.
> +
> +  For this, the cgroup has memory 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. Note that for a fine-grained
> +  control, you should probably use the shrinker interface, as described
> +  above.
> +
> +  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.)

Interface look okay for me.

BTW, do you track pressure level changes due changes in
memory[.memsw].limit_in_bytes or memory hotplug?

> diff --git a/Documentation/cgroups/mempressure_test.c b/Documentation/cgroups/mempressure_test.c
> new file mode 100644
> index 0000000..9747fd6
> --- /dev/null
> +++ b/Documentation/cgroups/mempressure_test.c
> @@ -0,0 +1,209 @@
> +/*
> + * mempressure shrinker test
> + *
> + * Copyright 2012 Linaro Ltd.
> + *		  Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
> + *
> + * It is pretty simple: we create two threads, the first one constantly
> + * tries to allocate memory (more than we physically have), the second
> + * thread listens to the kernel shrinker notifications and frees asked
> + * amount of chunks. When we allocate more than available RAM, the two
> + * threads start to fight. Idially, we should not OOM (but if we reclaim
> + * slower than we allocate, things might OOM). Also, ideally we should not
> + * grow swap too much.
> + *
> + * The test accepts no arguments, so you can just run it and observe the
> + * output and memory usage (e.g. 'watch -n 0.2 free -m'). Upon ctrl+c, the
> + * test prints total amount of bytes we helped to reclaim.
> + *
> + * Compile with -pthread.
> + *
> + * 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.
> + */
> +
> +#define _GNU_SOURCE
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <stdint.h>
> +#include <stdbool.h>
> +#include <unistd.h>
> +#include <string.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <fcntl.h>
> +#include <pthread.h>
> +#include <signal.h>
> +#include <errno.h>
> +#include <sys/eventfd.h>
> +#include <sys/sysinfo.h>
> +
> +#define CG			"/sys/fs/cgroup/mempressure"
> +#define CG_EVENT_CONTROL	(CG "/cgroup.event_control")
> +#define CG_SHRINKER		(CG "/mempressure.shrinker")
> +
> +#define CHUNK_SIZE (1 * 1024 * 1024)
> +
> +static size_t num_chunks;
> +
> +static void **chunks;
> +static pthread_mutex_t *locks;
> +static int efd;
> +static int sfd;
> +
> +static inline void pabort(bool f, int code, const char *str)
> +{
> +	if (!f)
> +		return;
> +	perror(str);
> +	printf("(%d)\n", code);
> +	abort();
> +}
> +
> +static void init_shrinker(void)
> +{
> +	int cfd;
> +	int ret;
> +	char *str;
> +
> +	cfd = open(CG_EVENT_CONTROL, O_WRONLY);
> +	pabort(cfd < 0, cfd, CG_EVENT_CONTROL);
> +
> +	sfd = open(CG_SHRINKER, O_RDWR);
> +	pabort(sfd < 0, sfd, CG_SHRINKER);
> +
> +	efd = eventfd(0, 0);
> +	pabort(efd < 0, efd, "eventfd()");
> +
> +	ret = asprintf(&str, "%d %d %d\n", efd, sfd, CHUNK_SIZE);
> +	printf("%s\n", str);

str value is undefined here if asprintf() failed.

> +	pabort(ret == -1, ret, "control string");
> +
> +	ret = write(cfd, str, ret + 1);
> +	pabort(ret == -1, ret, "write() to event_control");

str is leaked.

> +}
> +
> +static void add_reclaimable(int chunks)
> +{
> +	int ret;
> +	char *str;
> +
> +	ret = asprintf(&str, "%d %d\n", efd, CHUNK_SIZE);

s/CHUNK_SIZE/chunks/ ?

same problems with str here.

> +	pabort(ret == -1, ret, "add_reclaimable, asprintf");
> +
> +	ret = write(sfd, str, ret + 1);
> +	pabort(ret <= 0, ret, "add_reclaimable, write");
> +}
> +
> +static int chunks_to_reclaim(void)
> +{
> +	uint64_t n = 0;
> +	int ret;
> +
> +	ret = read(efd, &n, sizeof(n));
> +	pabort(ret <= 0, ret, "read() from eventfd");
> +
> +	printf("%d chunks to reclaim\n", (int)n);
> +
> +	return n;
> +}
> +
> +static unsigned int reclaimed;
> +
> +static void print_stats(int signum)
> +{
> +	printf("\nTOTAL: helped to reclaim %d chunks (%d MB)\n",
> +	       reclaimed, reclaimed * CHUNK_SIZE / 1024 / 1024);
> +	exit(0);
> +}
> +
> +static void *shrinker_thr_fn(void *arg)
> +{
> +	puts("shrinker thread started");
> +
> +	sigaction(SIGINT, &(struct sigaction){.sa_handler = print_stats}, NULL);
> +
> +	while (1) {
> +		unsigned int i = 0;
> +		int n;
> +
> +		n = chunks_to_reclaim();
> +
> +		reclaimed += n;
> +
> +		while (n) {
> +			pthread_mutex_lock(&locks[i]);
> +			if (chunks[i]) {
> +				free(chunks[i]);
> +				chunks[i] = NULL;
> +				n--;
> +			}
> +			pthread_mutex_unlock(&locks[i]);
> +
> +			i = (i + 1) % num_chunks;
> +		}
> +	}
> +	return NULL;
> +}
> +
> +static void consume_memory(void)
> +{
> +	unsigned int i = 0;
> +	unsigned int j = 0;
> +
> +	puts("consuming memory...");
> +
> +	while (1) {
> +		pthread_mutex_lock(&locks[i]);
> +		if (!chunks[i]) {
> +			chunks[i] = malloc(CHUNK_SIZE);
> +			pabort(!chunks[i], 0, "chunks alloc failed");
> +			memset(chunks[i], 0, CHUNK_SIZE);
> +			j++;
> +		}
> +		pthread_mutex_unlock(&locks[i]);
> +
> +		if (j >= num_chunks / 10) {
> +			add_reclaimable(num_chunks / 10);
> +			printf("added %d reclaimable chunks\n", j);
> +			j = 0;
> +		}
> +
> +		i = (i + 1) % num_chunks;
> +	}
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	int ret;
> +	int i;
> +	pthread_t shrinker_thr;
> +	struct sysinfo si;
> +
> +	ret = sysinfo(&si);
> +	pabort(ret != 0, ret, "sysinfo()");
> +
> +	num_chunks = (si.totalram + si.totalswap) * si.mem_unit / 1024 / 1024;
> +
> +	chunks = malloc(sizeof(*chunks) * num_chunks);
> +	locks = malloc(sizeof(*locks) * num_chunks);
> +	pabort(!chunks || !locks, ENOMEM, NULL);
> +
> +	init_shrinker();
> +
> +	for (i = 0; i < num_chunks; i++) {
> +		ret = pthread_mutex_init(&locks[i], NULL);
> +		pabort(ret != 0, ret, "pthread_mutex_init");
> +	}
> +
> +	ret = pthread_create(&shrinker_thr, NULL, shrinker_thr_fn, NULL);
> +	pabort(ret != 0, ret, "pthread_create(shrinker)");
> +
> +	consume_memory();
> +
> +	ret = pthread_join(shrinker_thr, NULL);
> +	pabort(ret != 0, ret, "pthread_join(shrinker)");
> +
> +	return 0;
> +}
> 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 92a86b2..3f7f7d2 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 6fdd6e3..5c308be 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -826,6 +826,18 @@ 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. This includes simple memory pressure
> +	  notifications and a full-fledged userland reclaimer.
> +
> +	  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 6b025f8..40cee19 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -50,6 +50,7 @@ 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..e39a33d
> --- /dev/null
> +++ b/mm/mempressure.c
> @@ -0,0 +1,488 @@
> +/*
> + * Linux VM pressure
> + *
> + * Copyright 2012 Linaro Ltd.
> + *		  Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
> + *
> + * 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.
> + *
> + * The same window size also used for the shrinker, so be aware. It might
> + * be a good idea to derive the window size from the machine size, similar
> + * to what we do for the vmstat.
> + */
> +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_shrinker {
> +	struct eventfd_ctx *efd;
> +	size_t chunks;
> +	size_t chunk_sz;
> +	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 list_head shrinkers;
> +	struct mutex shrinkers_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_shrinker(struct mpc_state *mpc, ulong s, ulong r)
> +{
> +	struct mpc_shrinker *sh;
> +	ssize_t to_reclaim_pages = s - r;
> +
> +	if (!to_reclaim_pages)
> +		return;
> +
> +	mutex_lock(&mpc->shrinkers_lock);
> +
> +	/*
> +	 * To make accounting more precise and to avoid excessive
> +	 * communication with the kernel, we operate on chunks instead of
> +	 * bytes. Say, asking to free 8 KBs makes little sense if
> +	 * granularity of allocations is 10 MBs. Also, knowing the
> +	 * granularity (chunk size) and the number of reclaimable chunks,
> +	 * we just ask that N chunks should be freed, and we assume that
> +	 * it will be freed, thus we decrement our internal counter
> +	 * straight away (i.e. userland does not need to respond how much
> +	 * was reclaimed). But, if userland could not free it, it is
> +	 * responsible to increment the counter back.
> +	 */
> +	list_for_each_entry(sh, &mpc->shrinkers, node) {
> +		size_t to_reclaim_chunks;
> +
> +		if (!sh->chunks)
> +			continue;
> +
> +		to_reclaim_chunks = to_reclaim_pages *
> +				    PAGE_SIZE / sh->chunk_sz;
> +		to_reclaim_chunks = min(sh->chunks, to_reclaim_chunks);
> +
> +		if (!to_reclaim_chunks)
> +			continue;
> +
> +		sh->chunks -= to_reclaim_chunks;
> +
> +		eventfd_signal(sh->efd, to_reclaim_chunks);
> +
> +		to_reclaim_pages -= to_reclaim_chunks *
> +				    sh->chunk_sz / PAGE_SIZE;
> +		if (to_reclaim_pages <= 0)
> +			break;
> +	}
> +
> +	mutex_unlock(&mpc->shrinkers_lock);
> +}
> +
> +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)

What about per-level lists?

> +			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_shrinker(mpc, s, r);
> +	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_create(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);
> +	mutex_init(&mpc->shrinkers_lock);
> +	INIT_LIST_HEAD(&mpc->events);
> +	INIT_LIST_HEAD(&mpc->shrinkers);
> +	INIT_WORK(&mpc->work, mpc_vmpressure_wk_fn);
> +
> +	return &mpc->css;
> +}
> +
> +static void mpc_destroy(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_event(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_event(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 int mpc_register_shrinker(struct cgroup *cg, struct cftype *cft,
> +				 struct eventfd_ctx *eventfd,
> +				 const char *args)
> +{
> +	struct mpc_state *mpc = cg2mpc(cg);
> +	struct mpc_shrinker *sh;
> +	ulong chunk_sz;
> +	int ret;
> +
> +	ret = kstrtoul(args, 10, &chunk_sz);
> +	if (ret)
> +		return ret;
> +
> +	sh = kzalloc(sizeof(*sh), GFP_KERNEL);
> +	if (!sh)
> +		return -ENOMEM;
> +
> +	sh->efd = eventfd;
> +	sh->chunk_sz = chunk_sz;
> +
> +	mutex_lock(&mpc->shrinkers_lock);
> +	list_add(&sh->node, &mpc->shrinkers);
> +	mutex_unlock(&mpc->shrinkers_lock);
> +
> +	return 0;
> +}
> +
> +static void mpc_unregister_shrinker(struct cgroup *cg, struct cftype *cft,
> +				 struct eventfd_ctx *eventfd)
> +{
> +	struct mpc_state *mpc = cg2mpc(cg);
> +	struct mpc_shrinker *sh;
> +
> +	mutex_lock(&mpc->shrinkers_lock);
> +	list_for_each_entry(sh, &mpc->shrinkers, node) {
> +		if (sh->efd != eventfd)
> +			continue;
> +		list_del(&sh->node);
> +		kfree(sh);
> +		break;
> +	}
> +	mutex_unlock(&mpc->shrinkers_lock);
> +}
> +
> +static int mpc_write_shrinker(struct cgroup *cg, struct cftype *cft,
> +			      const char *str)
> +{
> +	struct mpc_state *mpc = cg2mpc(cg);
> +	struct mpc_shrinker *sh;
> +	struct eventfd_ctx *eventfd;
> +	struct file *file;
> +	ssize_t chunks;
> +	int fd;
> +	int ret;
> +
> +	ret = sscanf(str, "%d %zd\n", &fd, &chunks);
> +	if (ret != 2)
> +		return -EINVAL;
> +
> +	file = fget(fd);
> +	if (!file)
> +		return -EBADF;
> +
> +	eventfd = eventfd_ctx_fileget(file);
> +
> +	mutex_lock(&mpc->shrinkers_lock);
> +
> +	/* Can avoid the loop once we introduce ->priv for eventfd_ctx. */
> +	list_for_each_entry(sh, &mpc->shrinkers, node) {
> +		if (sh->efd != eventfd)
> +			continue;
> +		if (chunks < 0 && abs(chunks) > sh->chunks)
> +			sh->chunks = 0;
> +		else
> +			sh->chunks += chunks;
> +		break;
> +	}
> +
> +	mutex_unlock(&mpc->shrinkers_lock);
> +
> +	eventfd_ctx_put(eventfd);
> +	fput(file);
> +
> +	return 0;
> +}
> +
> +static struct cftype mpc_files[] = {
> +	{
> +		.name = "level",
> +		.read = mpc_read_level,
> +		.register_event = mpc_register_level_event,
> +		.unregister_event = mpc_unregister_event,

mpc_unregister_level_event for consistency.

> +	},
> +	{
> +		.name = "shrinker",
> +		.register_event = mpc_register_shrinker,
> +		.unregister_event = mpc_unregister_shrinker,
> +		.write_string = mpc_write_shrinker,
> +	},
> +	{},
> +};
> +
> +struct cgroup_subsys mpc_cgroup_subsys = {
> +	.name = "mempressure",
> +	.subsys_id = mpc_cgroup_subsys_id,
> +	.create = mpc_create,
> +	.destroy = mpc_destroy,
> +	.base_cftypes = mpc_files,
> +};
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 48550c6..d8ff846 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1877,6 +1877,9 @@ 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))
> @@ -2099,6 +2102,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  		count_vm_event(ALLOCSTALL);
>  
>  	do {
> +		vmpressure_prio(sc->target_mem_cgroup, sc->priority);
>  		sc->nr_scanned = 0;
>  		aborted_reclaim = shrink_zones(zonelist, sc);
>  
> -- 
> 1.8.0

-- 
 Kirill A. Shutemov
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