On Fri, 20 Dec 2013 18:31:02 +0400 Glauber Costa <glommer@xxxxxxxxx> wrote: > > I have the exact problem described above for a project I'm working on > > and this solution seems to solve it well. > > > > However, I had a few issues while trying to use this interface. I'll > > comment on them below, but please take this more as advice seeking > > than patch review. > > > >> 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> > >> Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> > >> Acked-by: Anton Vorontsov <anton@xxxxxxxxxx> > >> Acked-by: Pekka Enberg <penberg@xxxxxxxxxx> > >> Reviewed-by: Greg Thelen <gthelen@xxxxxxxxxx> > >> Cc: Dave Chinner <dchinner@xxxxxxxxxx> > >> Cc: John Stultz <john.stultz@xxxxxxxxxx> > >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > >> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > >> Cc: Michal Hocko <mhocko@xxxxxxx> > >> Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > >> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > >> --- > >> include/linux/vmpressure.h | 5 +++++ > >> mm/vmpressure.c | 53 +++++++++++++++++++++++++++++++++++++++++--- > >> 2 files changed, 55 insertions(+), 3 deletions(-) > >> > >> diff --git a/include/linux/vmpressure.h b/include/linux/vmpressure.h > >> index 3f3788d..9102e53 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; > >> }; > >> > >> @@ -38,6 +41,8 @@ extern int vmpressure_register_event(struct cgroup_subsys_state *css, > >> struct cftype *cft, > >> struct eventfd_ctx *eventfd, > >> const char *args); > >> +extern int vmpressure_register_kernel_event(struct cgroup_subsys_state *css, > >> + void (*fn)(void)); > >> extern void vmpressure_unregister_event(struct cgroup_subsys_state *css, > >> struct cftype *cft, > >> struct eventfd_ctx *eventfd); > >> diff --git a/mm/vmpressure.c b/mm/vmpressure.c > >> index e0f6283..730e7c1 100644 > >> --- a/mm/vmpressure.c > >> +++ b/mm/vmpressure.c > >> @@ -130,8 +130,12 @@ 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); > > > > How does the callback access its private data? > > > >> + }; > >> enum vmpressure_levels level; > >> + bool kernel_event; > >> struct list_head node; > >> }; > >> > >> @@ -147,12 +151,15 @@ 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(); > > > > I think it would be interesting to pass 'level' to the callback (I'll > > probably use it myself), but we could wait for a in-tree user before > > adding it. > > > >> + } else if (vmpr->notify_userspace && level >= ev->level) { > >> eventfd_signal(ev->efd, 1); > >> signalled = true; > >> } > >> } > >> > >> + vmpr->notify_userspace = false; > >> mutex_unlock(&vmpr->events_lock); > >> > >> return signalled; > >> @@ -222,7 +229,7 @@ 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 > >> @@ -239,8 +246,15 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, > >> vmpr->scanned += scanned; > >> vmpr->reclaimed += reclaimed; > >> scanned = vmpr->scanned; > >> + /* > >> + * If we didn't reach this point, only kernel events will be triggered. > >> + * It is the job of the worker thread to clean this up once the > >> + * notifications are all delivered. > >> + */ > >> + vmpr->notify_userspace = true; > >> spin_unlock(&vmpr->sr_lock); > >> > >> +schedule: > >> if (scanned < vmpressure_win) > >> return; > >> schedule_work(&vmpr->work); > >> @@ -324,6 +338,39 @@ int vmpressure_register_event(struct cgroup_subsys_state *css, > >> } > >> > >> /** > >> + * vmpressure_register_kernel_event() - Register kernel-side notification > >> + * @css: css 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_subsys_state *css, > >> + void (*fn)(void)) > >> +{ > >> + struct vmpressure *vmpr = css_to_vmpressure(css); > > > > This doesn't allow for css=NULL. What's the recommended way for a today's > > shrinker (which is not related to cgroups) to register with this API? > > > > Also, you don't seem to provide a way to de-register from the event. > > > > The answer for all of your questions above can be summarized by noting > that for the lack of other users (at the time), this patch does the bare minimum > for memcg needs. I agree, for instance, that it would be good to pass the level > but since memcg won't do anything with thta, I didn't pass it. > > That should be extended if you need to. That works for me. That is, including this minimal version first and extending it when we get in-tree users. > > > I hacked a patch to be able to use this, seems to work but it's a ugly > > hack: > > > > --- > > include/linux/vmpressure.h | 3 ++- > > mm/vmpressure.c | 13 +++++++++---- > > 2 files changed, 11 insertions(+), 5 deletions(-) > > > > diff --git a/include/linux/vmpressure.h b/include/linux/vmpressure.h > > index 9102e53..de416b6 100644 > > --- a/include/linux/vmpressure.h > > +++ b/include/linux/vmpressure.h > > @@ -42,7 +42,8 @@ extern int vmpressure_register_event(struct cgroup_subsys_state *css, > > struct eventfd_ctx *eventfd, > > const char *args); > > extern int vmpressure_register_kernel_event(struct cgroup_subsys_state *css, > > - void (*fn)(void)); > > + void (*fn)(void *data, int level), > > + void *data); > > extern void vmpressure_unregister_event(struct cgroup_subsys_state *css, > > struct cftype *cft, > > struct eventfd_ctx *eventfd); > > diff --git a/mm/vmpressure.c b/mm/vmpressure.c > > index 730e7c1..4ed0e85 100644 > > --- a/mm/vmpressure.c > > +++ b/mm/vmpressure.c > > @@ -132,9 +132,10 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned, > > struct vmpressure_event { > > union { > > struct eventfd_ctx *efd; > > - void (*fn)(void); > > + void (*fn)(void *data, int level); > > }; > > enum vmpressure_levels level; > > + void *data; > > bool kernel_event; > > struct list_head node; > > }; > > @@ -152,7 +153,7 @@ static bool vmpressure_event(struct vmpressure *vmpr, > > > > list_for_each_entry(ev, &vmpr->events, node) { > > if (ev->kernel_event) { > > - ev->fn(); > > + ev->fn(ev->data, level); > > } else if (vmpr->notify_userspace && level >= ev->level) { > > eventfd_signal(ev->efd, 1); > > signalled = true; > > @@ -352,21 +353,25 @@ int vmpressure_register_event(struct cgroup_subsys_state *css, > > * well-defined cgroup aware interface. > > */ > > int vmpressure_register_kernel_event(struct cgroup_subsys_state *css, > > - void (*fn)(void)) > > + void (*fn)(void *data, int level), void *data) > > { > > - struct vmpressure *vmpr = css_to_vmpressure(css); > > + struct vmpressure *vmpr; > > struct vmpressure_event *ev; > > > > + vmpr = css ? css_to_vmpressure(css) : memcg_to_vmpressure(NULL); > > + > > ev = kzalloc(sizeof(*ev), GFP_KERNEL); > > if (!ev) > > return -ENOMEM; > > > > ev->kernel_event = true; > > + ev->data = data; > > ev->fn = fn; > > > > mutex_lock(&vmpr->events_lock); > > list_add(&ev->node, &vmpr->events); > > mutex_unlock(&vmpr->events_lock); > > + > > Your patch makes sense. > > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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