On Mon, 10 Jun 2013 20:14:13 +0900
Hyunhee Kim <hyunhee.kim@xxxxxxxxxxx> wrote:
> In vmpressure, events are sent to the user space continuously
> until the memory state changes. This becomes overheads for user space module
> and also consumes power consumption.
If the kernel is still under memory pressure, I think we do want to keep
sending the event to user-space. At least as a default behavior.
I think it would be fine to implement this change as an additional parameter
when registering for the event, but I also wonder if this shouldn't be
solved by the user-space app itself (eg. rate-limiting the event reception).
> So, with this patch, vmpressure
> remembers
> the current level and only sends the event only when new memory state is
> different from the current level.
>
> Signed-off-by: Hyunhee Kim <hyunhee.kim@xxxxxxxxxxx>
> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> ---
> include/linux/vmpressure.h | 2 ++
> mm/vmpressure.c | 4 +++-
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/vmpressure.h b/include/linux/vmpressure.h
> index 76be077..fa0c0d2 100644
> --- a/include/linux/vmpressure.h
> +++ b/include/linux/vmpressure.h
> @@ -20,6 +20,8 @@ struct vmpressure {
> struct mutex events_lock;
>
> struct work_struct work;
> +
> + int current_level;
> };
>
> struct mem_cgroup;
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 736a601..5f6609c 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -152,9 +152,10 @@ static bool vmpressure_event(struct vmpressure *vmpr,
> mutex_lock(&vmpr->events_lock);
>
> list_for_each_entry(ev, &vmpr->events, node) {
> - if (level >= ev->level) {
> + if (level >= ev->level && level != vmpr->current_level) {
> eventfd_signal(ev->efd, 1);
> signalled = true;
> + vmpr->current_level = level;
> }
> }
>
> @@ -371,4 +372,5 @@ void vmpressure_init(struct vmpressure *vmpr)
> mutex_init(&vmpr->events_lock);
> INIT_LIST_HEAD(&vmpr->events);
> INIT_WORK(&vmpr->work, vmpressure_work_fn);
> + vmpr->current_level = -1;
> }
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