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Date: Thu, 3 May 2012 10:24:42 +0300 (EEST) From: Pekka Enberg <penberg@...nel.org> To: Minchan Kim <minchan@...nel.org> cc: linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>, Anton Vorontsov <anton.vorontsov@...aro.org>, Leonid Moiseichuk <leonid.moiseichuk@...ia.com> Subject: Re: vmevent: question? On Mon, 30 Apr 2012, Minchan Kim wrote: > > What kind of consistency guarantees do you mean? The data sent to > > userspace is always a snapshot of the state and therefore can be stale > > by the time it reaches userspace. > > Consistency between component of snapshot. > let's assume following as > > 1. User expect some events's value would be minus when event he expect happen. > A : -3, B : -4, C : -5, D : -6 > 2. Logically, it's not possible to mix plus and minus values for the events. > A : -3, B : -4, C : -5, D : -6 ( O ) > A : -3, B : -4, C : 1, D : 2 ( X ) > > But in current implementation, some of those could be minus and some of those could be plus. > Which event could user believe? > At least, we need a _captured_ value when event triggered so that user can ignore other values. Sorry, I still don't quite understand the problem. The current implementation provides the same kind of snapshot consistency as reading from /proc/vmstat does (modulo the fact that we read them twice) for the values we support. Pekka -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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