Messages in this thread | | | Date | Wed, 18 Jan 2012 11:15:41 +0200 | Subject | Re: [RFC 1/3] /dev/low_mem_notify | From | Pekka Enberg <> |
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On Wed, Jan 18, 2012 at 11:06 AM, <leonid.moiseichuk@nokia.com> 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, <leonid.moiseichuk@nokia.com> 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.
>> +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, <leonid.moiseichuk@nokia.com> wrote: >> +static void vmnotify_sample(struct vmnotify_watch *watch) { > ... >> + 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 :-).
>> +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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