On Tue, Apr 23 2013, Glauber Costa wrote:
> From: Glauber Costa <glommer@xxxxxxxxxxxxx>
>
> During the past weeks, it became clear to us that the shrinker interface
> we have right now works very well for some particular types of users,
> but not that well for others. The later are usually people interested in
> one-shot notifications, that were forced to adapt themselves to the
> count+scan behavior of shrinkers. To do so, they had no choice than to
> greatly abuse the shrinker interface producing little monsters all over.
>
> During LSF/MM, one of the proposals that popped out during our session
> was to reuse Anton Voronstsov's vmpressure for this. They are designed
> for userspace consumption, but also provide a well-stablished,
> cgroup-aware entry point for notifications.
>
> This patch extends that to also support in-kernel users. Events that
> should be generated for in-kernel consumption will be marked as such,
> and for those, we will call a registered function instead of triggering
> an eventfd notification.
>
> Please note that due to my lack of understanding of each shrinker user,
> I will stay away from converting the actual users, you are all welcome
> to do so.
>
> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Cc: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
> Cc: John Stultz <john.stultz@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Joonsoo Kim <js1304@xxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
> include/linux/vmpressure.h | 6 ++++++
> mm/vmpressure.c | 48 ++++++++++++++++++++++++++++++++++++++++++----
> 2 files changed, 50 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/vmpressure.h b/include/linux/vmpressure.h
> index 76be077..1862012 100644
> --- a/include/linux/vmpressure.h
> +++ b/include/linux/vmpressure.h
> @@ -19,6 +19,9 @@ struct vmpressure {
> /* Have to grab the lock on events traversal or modifications. */
> struct mutex events_lock;
>
> + /* false if only kernel users want to be notified, true otherwise */
> + bool notify_userspace;
> +
> struct work_struct work;
> };
>
> @@ -36,6 +39,9 @@ extern struct vmpressure *css_to_vmpressure(struct cgroup_subsys_state *css);
> extern int vmpressure_register_event(struct cgroup *cg, struct cftype *cft,
> struct eventfd_ctx *eventfd,
> const char *args);
> +
> +extern int vmpressure_register_kernel_event(struct cgroup *cg,
> + void (*fn)(void));
> extern void vmpressure_unregister_event(struct cgroup *cg, struct cftype *cft,
> struct eventfd_ctx *eventfd);
> #else
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 736a601..8d77ad0 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -135,8 +135,12 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
> }
>
> struct vmpressure_event {
> - struct eventfd_ctx *efd;
> + union {
> + struct eventfd_ctx *efd;
> + void (*fn)(void);
> + };
> enum vmpressure_levels level;
> + bool kernel_event;
> struct list_head node;
> };
>
> @@ -152,7 +156,9 @@ 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 (ev->kernel_event)
> + ev->fn();
> + else if (vmpr->notify_userspace && (level >= ev->level)) {
> eventfd_signal(ev->efd, 1);
> signalled = true;
> }
> @@ -227,7 +233,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
> * we account it too.
> */
> if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
> - return;
> + goto schedule;
>
> /*
> * If we got here with no pages scanned, then that is an indicator
> @@ -238,14 +244,16 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
> * through vmpressure_prio(). But so far, keep calm.
> */
> if (!scanned)
> - return;
> + goto schedule;
>
> mutex_lock(&vmpr->sr_lock);
> vmpr->scanned += scanned;
> vmpr->reclaimed += reclaimed;
> + vmpr->notify_userspace = true;
Should notify_userspace get cleared sometime? Seems like we might need
to clear or decrement notify_userspace in vmpressure_event() when
calling eventfd_signal().
> scanned = vmpr->scanned;
> mutex_unlock(&vmpr->sr_lock);
>
> +schedule:
> if (scanned < vmpressure_win || work_pending(&vmpr->work))
> return;
> schedule_work(&vmpr->work);
> @@ -328,6 +336,38 @@ int vmpressure_register_event(struct cgroup *cg, struct cftype *cft,
> }
>
> /**
> + * vmpressure_register_kernel_event() - Register kernel-side notification
> + * @cg: cgroup that is interested in vmpressure notifications
> + * @fn: function to be called when pressure happens
> + *
> + * This function register in-kernel users interested in receiving notifications
> + * about pressure conditions. Pressure notifications will be triggered at the
> + * same time as userspace notifications (with no particular ordering relative
> + * to it).
> + *
> + * Pressure notifications are a alternative method to shrinkers and will serve
> + * well users that are interested in a one-shot notification, with a
> + * well-defined cgroup aware interface.
> + */
> +int vmpressure_register_kernel_event(struct cgroup *cg, void (*fn)(void))
> +{
> + struct vmpressure *vmpr = cg_to_vmpressure(cg);
> + struct vmpressure_event *ev;
> +
> + ev = kzalloc(sizeof(*ev), GFP_KERNEL);
> + if (!ev)
> + return -ENOMEM;
> +
> + ev->kernel_event = true;
> + ev->fn = fn;
> +
> + mutex_lock(&vmpr->events_lock);
> + list_add(&ev->node, &vmpr->events);
> + mutex_unlock(&vmpr->events_lock);
> + return 0;
> +}
> +
> +/**
> * vmpressure_unregister_event() - Unbind eventfd from vmpressure
> * @cg: cgroup handle
> * @cft: cgroup control files handle
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