On Wed, Jan 18, 2012 at 11:06 AM,  [off-list ref] wrote:

Would be possible to not use percents for thesholds? Accounting in pages even
not so difficult to user-space.

How does that work with memory hotplug?

On Wed, Jan 18, 2012 at 11:06 AM,  [off-list ref] wrote:

Also, looking on vmnotify_match I understand that events propagated to
user-space only in case threshold trigger change state from 0 to 1 but not
back, 1-> 0 is very useful event as well.

Would be possible to use for threshold pointed value(s) e.g. according to
enum zone_state_item, because kinds of memory to track could be different?
E.g. to tracking paging activity NR_ACTIVE_ANON and NR_ACTIVE_FILE could be
interesting, not only free.

I don't think there's anything in the ABI that would prevent that.

quoted

+struct vmnotify_event {
+     /* Size of the struct for ABI extensibility. */
+     __u32                   size;
+
+     __u64                   nr_avail_pages;
+
+     __u64                   nr_swap_pages;
+
+     __u64                   nr_free_pages;
+};

Two fields here most likely session-constant, (nr_avail_pages and
nr_swap_pages), seems not much sense to report them in every event.  If we
have memory/swap hotplug user-space can use sysinfo() call.

I actually changed the ABI to look like this:

struct vmnotify_event {
        /*
         * Size of the struct for ABI extensibility.
         */
        __u32                   size;

        __u64                   attrs;

        __u64                   attr_values[];
};

So userspace can decide which fields to include in notifications.

On Wed, Jan 18, 2012 at 11:06 AM,  [off-list ref] wrote:

quoted

+static void vmnotify_sample(struct vmnotify_watch *watch) {

...

quoted

+     si_meminfo(&si);
+     event.nr_avail_pages    = si.totalram;
+
+#ifdef CONFIG_SWAP
+     si_swapinfo(&si);
+     event.nr_swap_pages     = si.totalswap;
+#endif
+

Why not to use global_page_state() directly? si_meminfo() and especial
si_swapinfo are quite expensive call.

Sure, we can do that. Feel free to send a patch :-).

quoted

+static void vmnotify_start_timer(struct vmnotify_watch *watch) {
+     u64 sample_period = watch->config.sample_period_ns;
+
+     hrtimer_init(&watch->timer, CLOCK_MONOTONIC,
HRTIMER_MODE_REL);
+     watch->timer.function = vmnotify_timer_fn;
+
+     hrtimer_start(&watch->timer, ns_to_ktime(sample_period),
+HRTIMER_MODE_REL_PINNED); }

Do I understand correct you allocate timer for every user-space client and
propagate events every pointed interval?  What will happened with system if
we have a timer but need to turn CPU off? The timer must not be a reason to
wakeup if user-space is sleeping.

No idea what happens. The sampling code is just a proof of concept thing and I
expect it to be buggy as hell. :-)

			Pekka

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