linux-kernel - Re: vmevent: question?

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Message-ID: <4FA23E47.6040303@kernel.org>
Date:	Thu, 03 May 2012 17:13:59 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Pekka Enberg <penberg@...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 05/03/2012 05:07 PM, Pekka Enberg wrote:

> On Thu, May 3, 2012 at 10:57 AM, Minchan Kim <minchan@...nel.org> wrote:
>> Sorry for my poor explanation.
>> My point is when userspace get vmevent_event by reading fd, it could enumerate
>> several attribute all at once.
>> Then, one of attribute(call A) made by vmevent_match in kernel and other attributes(call B, C, D)
>> are just extra for convenience. Because there is time gap when kernel get attribute values, B,C,D could be stale.
>> Then, how can user determine which event is really triggered? A or B or C or D?
>> Which event really happens?
> 
> Right. Mark the matching values with something like
> VMEVENT_ATTR_STATE_CAPTURED should be sufficient?


Seems to be good and we have to notice to user by document
"Except VMEVENT_ATTR_STATE_CAPTURED, all attributes's value could be stale.
So, don't be deceived. Please ignore if you need"

First of all, let make CAPTURED state could be exact.

-----
> Q 2. Is it okay although value when vmevent_match check happens is different with
>     vmevent_sample_attr in vmevent_sample's for loop?
>     I think it's not good.
Yeah, that's just silly and needs fixing.
-----

> 
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-- 
Kind regards,
Minchan Kim
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