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Message-ID: <cc557aab1003080032u3451fb53u8ece3abf2d3f4852@mail.gmail.com>
Date: Mon, 8 Mar 2010 10:32:59 +0200
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/2] memcg: oom notifier
On Mon, Mar 8, 2010 at 9:25 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> Considering containers or other resource management softwares in userland,
> event notification of OOM in memcg should be implemented.
> Now, memcg has "threshold" notifier which uses eventfd, we can make
> use of it for oom notification.
>
> This patch adds oom notification eventfd callback for memcg. The usage
> is very similar to threshold notifier, but control file is
> memory.oom_control and no arguments other than eventfd is required.
>
> % cgroup_event_notifier /cgroup/A/memory.oom_control dummy
> (About cgroup_event_notifier, see Documentation/cgroup/)
Nice idea!
But I don't think that sharing mem_cgroup_(un)register_event()
with thresholds is a good idea. There are too many
"if (type != _OOM_TYPE)". Probably, it's cleaner to create separate
register/unregister for oom events, since oom event is quite different
from threshold. We, also, don't need RCU for oom events. It's not
a critical path.
> TODO:
> - add a knob to disable oom-kill under a memcg.
> - add read/write function to oom_control
>
> Changelog: 20100304
> - renewed implemnation.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> Documentation/cgroups/memory.txt | 20 ++++-
> mm/memcontrol.c | 155 ++++++++++++++++++++++++++++-----------
> 2 files changed, 131 insertions(+), 44 deletions(-)
>
> Index: mmotm-2.6.33-Mar5/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.33-Mar5.orig/mm/memcontrol.c
> +++ mmotm-2.6.33-Mar5/mm/memcontrol.c
> @@ -159,6 +159,7 @@ struct mem_cgroup_threshold_ary {
> };
>
> static void mem_cgroup_threshold(struct mem_cgroup *mem);
> +static void mem_cgroup_oom_notify(struct mem_cgroup *mem);
>
> /*
> * The memory controller data structure. The memory controller controls both
> @@ -220,6 +221,9 @@ struct mem_cgroup {
> /* thresholds for mem+swap usage. RCU-protected */
> struct mem_cgroup_threshold_ary *memsw_thresholds;
>
> + /* For oom notifier event fd */
> + struct mem_cgroup_threshold_ary *oom_notify;
> +
> /*
> * Should we move charges of a task when a task is moved into this
> * mem_cgroup ? And what type of charges should we move ?
> @@ -282,9 +286,12 @@ enum charge_type {
> /* for encoding cft->private value on file */
> #define _MEM (0)
> #define _MEMSWAP (1)
> +#define _OOM_TYPE (2)
> #define MEMFILE_PRIVATE(x, val) (((x) << 16) | (val))
> #define MEMFILE_TYPE(val) (((val) >> 16) & 0xffff)
> #define MEMFILE_ATTR(val) ((val) & 0xffff)
> +/* Used for OOM nofiier */
> +#define OOM_CONTROL (0)
>
> /*
> * Reclaim flags for mem_cgroup_hierarchical_reclaim
> @@ -1313,9 +1320,10 @@ bool mem_cgroup_handle_oom(struct mem_cg
> prepare_to_wait(&memcg_oom_waitq, &wait, TASK_KILLABLE);
> mutex_unlock(&memcg_oom_mutex);
>
> - if (locked)
> + if (locked) {
> + mem_cgroup_oom_notify(mem);
> mem_cgroup_out_of_memory(mem, mask);
> - else {
> + } else {
> schedule();
> finish_wait(&memcg_oom_waitq, &wait);
> }
> @@ -3363,33 +3371,65 @@ static int compare_thresholds(const void
> return _a->threshold - _b->threshold;
> }
>
> +static int mem_cgroup_oom_notify_cb(struct mem_cgroup *mem, void *data)
> +{
> + struct mem_cgroup_threshold_ary *x;
> + int i;
> +
> + rcu_read_lock();
> + x = rcu_dereference(mem->oom_notify);
> + for (i = 0; x && i < x->size; i++)
> + eventfd_signal(x->entries[i].eventfd, 1);
> + rcu_read_unlock();
> + return 0;
> +}
> +
> +static void mem_cgroup_oom_notify(struct mem_cgroup *mem)
> +{
> + mem_cgroup_walk_tree(mem, NULL, mem_cgroup_oom_notify_cb);
> +}
> +
> static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft,
> struct eventfd_ctx *eventfd, const char *args)
> {
> struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> struct mem_cgroup_threshold_ary *thresholds, *thresholds_new;
> int type = MEMFILE_TYPE(cft->private);
> - u64 threshold, usage;
> + u64 threshold;
> + u64 usage = 0;
> int size;
> int i, ret;
>
> - ret = res_counter_memparse_write_strategy(args, &threshold);
> - if (ret)
> - return ret;
> + if (type != _OOM_TYPE) {
> + ret = res_counter_memparse_write_strategy(args, &threshold);
> + if (ret)
> + return ret;
> + } else if (mem_cgroup_is_root(memcg)) /* root cgroup ? */
> + return -ENOTSUPP;
>
> mutex_lock(&memcg->thresholds_lock);
> - if (type == _MEM)
> + /* For waiting OOM notify, "-1" is passed */
> +
> + switch (type) {
> + case _MEM:
> thresholds = memcg->thresholds;
> - else if (type == _MEMSWAP)
> + break;
> + case _MEMSWAP:
> thresholds = memcg->memsw_thresholds;
> - else
> + break;
> + case _OOM_TYPE:
> + thresholds = memcg->oom_notify;
> + break;
> + default:
> BUG();
> + }
>
> - usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
> -
> - /* Check if a threshold crossed before adding a new one */
> - if (thresholds)
> - __mem_cgroup_threshold(memcg, type == _MEMSWAP);
> + if (type != _OOM_TYPE) {
> + usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
> + /* Check if a threshold crossed before adding a new one */
> + if (thresholds)
> + __mem_cgroup_threshold(memcg, type == _MEMSWAP);
> + }
>
> if (thresholds)
> size = thresholds->size + 1;
> @@ -3416,27 +3456,34 @@ static int mem_cgroup_register_event(str
> thresholds_new->entries[size - 1].threshold = threshold;
>
> /* Sort thresholds. Registering of new threshold isn't time-critical */
> - sort(thresholds_new->entries, size,
> + if (type != _OOM_TYPE) {
> + sort(thresholds_new->entries, size,
> sizeof(struct mem_cgroup_threshold),
> compare_thresholds, NULL);
> -
> - /* Find current threshold */
> - atomic_set(&thresholds_new->current_threshold, -1);
> - for (i = 0; i < size; i++) {
> - if (thresholds_new->entries[i].threshold < usage) {
> - /*
> - * thresholds_new->current_threshold will not be used
> - * until rcu_assign_pointer(), so it's safe to increment
> - * it here.
> - */
> - atomic_inc(&thresholds_new->current_threshold);
> + /* Find current threshold */
> + atomic_set(&thresholds_new->current_threshold, -1);
> + for (i = 0; i < size; i++) {
> + if (thresholds_new->entries[i].threshold < usage) {
> + /*
> + * thresholds_new->current_threshold will not
> + * be used until rcu_assign_pointer(), so it's
> + * safe to increment it here.
> + */
> + atomic_inc(&thresholds_new->current_threshold);
> + }
> }
> }
> -
> - if (type == _MEM)
> + switch (type) {
> + case _MEM:
> rcu_assign_pointer(memcg->thresholds, thresholds_new);
> - else
> + break;
> + case _MEMSWAP:
> rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
> + break;
> + case _OOM_TYPE:
> + rcu_assign_pointer(memcg->oom_notify, thresholds_new);
> + break;
> + }
>
> /* To be sure that nobody uses thresholds before freeing it */
> synchronize_rcu();
> @@ -3454,17 +3501,25 @@ static int mem_cgroup_unregister_event(s
> struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> struct mem_cgroup_threshold_ary *thresholds, *thresholds_new;
> int type = MEMFILE_TYPE(cft->private);
> - u64 usage;
> + u64 usage = 0;
> int size = 0;
> int i, j, ret;
>
> mutex_lock(&memcg->thresholds_lock);
> - if (type == _MEM)
> + /* check eventfd is for OOM check or not */
> + switch (type) {
> + case _MEM:
> thresholds = memcg->thresholds;
> - else if (type == _MEMSWAP)
> + break;
> + case _MEMSWAP:
> thresholds = memcg->memsw_thresholds;
> - else
> + break;
> + case _OOM_TYPE:
> + thresholds = memcg->oom_notify;
> + break;
> + default:
> BUG();
> + }
>
> /*
> * Something went wrong if we trying to unregister a threshold
> @@ -3472,11 +3527,11 @@ static int mem_cgroup_unregister_event(s
> */
> BUG_ON(!thresholds);
>
> - usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
> -
> - /* Check if a threshold crossed before removing */
> - __mem_cgroup_threshold(memcg, type == _MEMSWAP);
> -
> + if (type != _OOM_TYPE) {
> + usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
> + /* Check if a threshold crossed before removing */
> + __mem_cgroup_threshold(memcg, type == _MEMSWAP);
> + }
> /* Calculate new number of threshold */
> for (i = 0; i < thresholds->size; i++) {
> if (thresholds->entries[i].eventfd != eventfd)
> @@ -3500,13 +3555,15 @@ static int mem_cgroup_unregister_event(s
> thresholds_new->size = size;
>
> /* Copy thresholds and find current threshold */
> - atomic_set(&thresholds_new->current_threshold, -1);
> + if (type != _OOM_TYPE)
> + atomic_set(&thresholds_new->current_threshold, -1);
> for (i = 0, j = 0; i < thresholds->size; i++) {
> if (thresholds->entries[i].eventfd == eventfd)
> continue;
>
> thresholds_new->entries[j] = thresholds->entries[i];
> - if (thresholds_new->entries[j].threshold < usage) {
> + if (type != _OOM_TYPE &&
> + thresholds_new->entries[j].threshold < usage) {
> /*
> * thresholds_new->current_threshold will not be used
> * until rcu_assign_pointer(), so it's safe to increment
> @@ -3518,11 +3575,17 @@ static int mem_cgroup_unregister_event(s
> }
>
> assign:
> - if (type == _MEM)
> + switch (type) {
> + case _MEM:
> rcu_assign_pointer(memcg->thresholds, thresholds_new);
> - else
> + break;
> + case _MEMSWAP:
> rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
> -
> + break;
> + case _OOM_TYPE:
> + rcu_assign_pointer(memcg->oom_notify, thresholds_new);
> + break;
> + }
> /* To be sure that nobody uses thresholds before freeing it */
> synchronize_rcu();
>
> @@ -3588,6 +3651,12 @@ static struct cftype mem_cgroup_files[]
> .read_u64 = mem_cgroup_move_charge_read,
> .write_u64 = mem_cgroup_move_charge_write,
> },
> + {
> + .name = "oom_control",
> + .register_event = mem_cgroup_register_event,
> + .unregister_event = mem_cgroup_unregister_event,
> + .private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
> + },
> };
>
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> Index: mmotm-2.6.33-Mar5/Documentation/cgroups/memory.txt
> ===================================================================
> --- mmotm-2.6.33-Mar5.orig/Documentation/cgroups/memory.txt
> +++ mmotm-2.6.33-Mar5/Documentation/cgroups/memory.txt
> @@ -184,6 +184,9 @@ limits on the root cgroup.
>
> Note2: When panic_on_oom is set to "2", the whole system will panic.
>
> +When oom event notifier is registered, event will be delivered.
> +(See oom_control section)
> +
> 2. Locking
>
> The memory controller uses the following hierarchy
> @@ -486,7 +489,22 @@ threshold in any direction.
>
> It's applicable for root and non-root cgroup.
>
> -10. TODO
> +10. OOM Control
> +
> +Memory controler implements oom notifier using cgroup notification
> +API (See cgroups.txt). It allows to register multiple oom notification
> +delivery and gets notification when oom happens.
> +
> +To register a notifier, application need:
> + - create an eventfd using eventfd(2)
> + - open memory.oom_control file
> + - write string like "<event_fd> <memory.oom_control>" to cgroup.event_control
> +
> +Application will be notifier through eventfd when oom happens.
> +OOM notification doesn't work for root cgroup.
> +
> +
> +11. TODO
>
> 1. Add support for accounting huge pages (as a separate controller)
> 2. Make per-cgroup scanner reclaim not-shared pages first
>
> --
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