From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx178.postini.com [74.125.245.178]) by kanga.kvack.org (Postfix) with SMTP id D087C6B004D for ; Wed, 18 Jan 2012 04:15:42 -0500 (EST) Received: by obbta7 with SMTP id ta7so5040430obb.14 for ; Wed, 18 Jan 2012 01:15:41 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <84FF21A720B0874AA94B46D76DB98269045596AE@008-AM1MPN1-003.mgdnok.nokia.com> References: <1326788038-29141-1-git-send-email-minchan@kernel.org> <1326788038-29141-2-git-send-email-minchan@kernel.org> <4F15A34F.40808@redhat.com> <84FF21A720B0874AA94B46D76DB98269045596AE@008-AM1MPN1-003.mgdnok.nokia.com> Date: Wed, 18 Jan 2012 11:15:41 +0200 Message-ID: Subject: Re: [RFC 1/3] /dev/low_mem_notify From: Pekka Enberg Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: leonid.moiseichuk@nokia.com Cc: riel@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kamezawa.hiroyu@jp.fujitsu.com, mel@csn.ul.ie, rientjes@google.com, kosaki.motohiro@gmail.com, hannes@cmpxchg.org, mtosatti@redhat.com, akpm@linux-foundation.org, rhod@redhat.com, kosaki.motohiro@jp.fujitsu.com On Wed, Jan 18, 2012 at 11:06 AM, 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, 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, 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org