linux-kernel - Re: vmevent: question?

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Message-ID: <20120430075417.GA8438@lizard>
Date:	Mon, 30 Apr 2012 00:54:18 -0700
From:	Anton Vorontsov <cbouatmailru@...il.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>
Subject: Re: vmevent: question?

Hello Pekka,

On Mon, Apr 30, 2012 at 10:35:02AM +0300, Pekka Enberg wrote:
> > vmevent_smaple gathers all registered values to report to user if vmevent match.
> > But the time gap between vmevent match check and vmevent_sample_attr could make error
> > so user could confuse.
> >
> > Q 1. Why do we report _all_ registered vmstat value?
> >     In my opinion, it's okay just to report _a_ value vmevent_match happens.
> 
> It makes the userspace side simpler for "lowmem notification" use
> case. I'm open to changing the ABI if it doesn't make the userspace
> side too complex.

Yep. Actually, I'd like to add something like 'file_pages - shmem'
attribute, and reporting both (i.e. this new attr and free_pages)
values at the same time (even if just one crossed the threshold).

Reporting all the values would help userspace logic (so it won't
need to read /proc again).

> > Q 4. Do you have any plan for this patchset to merge into mainline?
> 
> Yes, I'm interested in pushing it forward if we can show that the ABI
> makes sense, is stable and generic enough, and fixes real world
> problems.

It seems to be a pretty nice driver. Speaking of ABI, the only thing
I personally dislike is VMEVENT_CONFIG_MAX_ATTRS (i.e. fixed-size
array in vmevent_config)... but I guess it's pretty easy to make
it variable-sized array... was there any particular reason to make
the _MAX thing?

Thanks!

-- 
Anton Vorontsov
Email: cbouatmailru@...il.com
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