linux-kernel - RE: [PATCH] vmevent: Use 'struct vmevent_attr' for vmevent

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Message-ID: <84FF21A720B0874AA94B46D76DB9826904581EF7@008-AM1MPN1-003.mgdnok.nokia.com>
Date:	Wed, 7 Mar 2012 07:53:37 +0000
From:	<leonid.moiseichuk@...ia.com>
To:	<anton.vorontsov@...aro.org>, <penberg@...nel.org>
CC:	<linux-kernel@...r.kernel.org>, <rientjes@...gle.com>
Subject: RE: [PATCH] vmevent: Use 'struct vmevent_attr' for vmevent_fd() ABI

> -----Original Message-----
> From: ext Anton Vorontsov [mailto:anton.vorontsov@...aro.org]
> Sent: 07 March, 2012 01:00
> To: Pekka Enberg
> Cc: linux-kernel@...r.kernel.org; Moiseichuk Leonid (Nokia-MP/Espoo);
...
> Sorry for hijacking this thread, but speaking of big changes. Are there any
> plans or ideas to add other methods of sampling, i.e. something not timer-
> based?
...
> Though, current vmevent seems not so lightweigh in sense of battery usage
> and accuracy (i.e. how quick we're able to detect the crossed threshold). To
> get better accuracy we would need to run timer at higher frequencies, but
> then we would waste more battery.

One of patch I sent was about switching to deferred timer. This API should not be 100% accurate first, and using deferred
timers will allow to sleep properly when system has no activity. I hope Pekka will accept the next patch as well.

> 
> Sure, vmevent is still lightweight in sense that it does not cause much
> runtime overhead or memory wastage (unlike cgroups).

"Timer work" is really lightweight.

> 
> The only idea I have for vmevent is to make some hybrid: timer plus shrinker
> API. That way we would detect "low memory" events fast enough via
> shrinker API, and thus run timer at low freq.

I used the same, see post about memnotify. Shrinker roll timer to be triggered soon.