Re: vmevent: question?

On Mon, 30 Apr 2012, Minchan Kim wrote:

quoted

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

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