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Date: Wed, 26 Jun 2013 10:12:15 +0900
From: Hyunhee Kim <hyunhee.kim@...sung.com>
To: Kyungmin Park <kmpark@...radead.org>,
Luiz Capitulino <lcapitulino@...hat.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, mhocko@...e.cz, minchan@...nel.org,
anton@...msg.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] vmpressure: implement strict mode
Please see "[PATCH v3] memcg: event control at vmpressure". mail
thread. (and also the thread I sent last Saturday.)
There was discussion on this mode not sending lower events when "level
!= ev->level".
Thanks,
Hyunhee Kim.
2013/6/26 Kyungmin Park <kmpark@...radead.org>:
> + Ms. Kim,
>
> she already raised this issue at another mail thread.
>
> Thank you,
> Kyungmin Park
>
> On Wed, Jun 26, 2013 at 6:51 AM, Luiz Capitulino <lcapitulino@...hat.com> wrote:
>> Currently, applications are notified for the level they registered for
>> _plus_ higher levels.
>>
>> This is a problem if the application wants to implement different
>> actions for different levels. For example, an application might want
>> to release 10% of its cache on level low, 50% on medium and 100% on
>> critical. To do this, the application has to register a different fd
>> for each event. However, fd low is always going to be notified and
>> and all fds are going to be notified on level critical.
>>
>> Strict mode solves this problem by strictly notifiying the event
>> an fd has registered for. It's optional. By default we still notify
>> on higher levels.
>>
>> Signed-off-by: Luiz Capitulino <lcapitulino@...hat.com>
>> ---
>>
>> PS: I'm following the discussion on the event storm problem, but I believe
>> strict mode is orthogonal to what has been suggested (although the
>> patches conflict)
>>
>> Documentation/cgroups/memory.txt | 10 ++++++----
>> mm/vmpressure.c | 19 +++++++++++++++++--
>> 2 files changed, 23 insertions(+), 6 deletions(-)
>>
>> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
>> index ddf4f93..3c589cf 100644
>> --- a/Documentation/cgroups/memory.txt
>> +++ b/Documentation/cgroups/memory.txt
>> @@ -807,12 +807,14 @@ register a notification, an application must:
>>
>> - create an eventfd using eventfd(2);
>> - open memory.pressure_level;
>> -- write string like "<event_fd> <fd of memory.pressure_level> <level>"
>> +- write string like "<event_fd> <fd of memory.pressure_level> <level> [strict]"
>> to cgroup.event_control.
>>
>> -Application will be notified through eventfd when memory pressure is at
>> -the specific level (or higher). Read/write operations to
>> -memory.pressure_level are no implemented.
>> +Applications will be notified through eventfd when memory pressure is at
>> +the specific level or higher. If strict is passed, then applications
>> +will only be notified when memory pressure reaches the specified level.
>> +
>> +Read/write operations to memory.pressure_level are no implemented.
>>
>> Test:
>>
>> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
>> index 736a601..6289ede 100644
>> --- a/mm/vmpressure.c
>> +++ b/mm/vmpressure.c
>> @@ -137,6 +137,7 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
>> struct vmpressure_event {
>> struct eventfd_ctx *efd;
>> enum vmpressure_levels level;
>> + bool strict_mode;
>> struct list_head node;
>> };
>>
>> @@ -153,6 +154,9 @@ static bool vmpressure_event(struct vmpressure *vmpr,
>>
>> list_for_each_entry(ev, &vmpr->events, node) {
>> if (level >= ev->level) {
>> + /* strict mode ensures level == ev->level */
>> + if (ev->strict_mode && level != ev->level)
>> + continue;
>> eventfd_signal(ev->efd, 1);
>> signalled = true;
>> }
>> @@ -292,7 +296,7 @@ void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
>> * infrastructure, so that the notifications will be delivered to the
>> * @eventfd. The @args parameter is a string that denotes pressure level
>> * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or
>> - * "critical").
>> + * "critical") and optionally a different operating mode (i.e. "strict")
>> *
>> * This function should not be used directly, just pass it to (struct
>> * cftype).register_event, and then cgroup core will handle everything by
>> @@ -303,22 +307,33 @@ int vmpressure_register_event(struct cgroup *cg, struct cftype *cft,
>> {
>> struct vmpressure *vmpr = cg_to_vmpressure(cg);
>> struct vmpressure_event *ev;
>> + bool smode = false;
>> + const char *p;
>> int level;
>>
>> for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) {
>> - if (!strcmp(vmpressure_str_levels[level], args))
>> + p = vmpressure_str_levels[level];
>> + if (!strncmp(p, args, strlen(p)))
>> break;
>> }
>>
>> if (level >= VMPRESSURE_NUM_LEVELS)
>> return -EINVAL;
>>
>> + p = strchr(args, ' ');
>> + if (p) {
>> + if (strncmp(++p, "strict", 6))
>> + return -EINVAL;
>> + smode = true;
>> + }
>> +
>> ev = kzalloc(sizeof(*ev), GFP_KERNEL);
>> if (!ev)
>> return -ENOMEM;
>>
>> ev->efd = eventfd;
>> ev->level = level;
>> + ev->strict_mode = smode;
>>
>> mutex_lock(&vmpr->events_lock);
>> list_add(&ev->node, &vmpr->events);
>> --
>> 1.8.1.4
>>
>> --
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>
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