linux-kernel - Re: [PATCH] vmpressure: implement strict mode

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Date:	Tue, 25 Jun 2013 21:03:31 -0700
From:	Anton Vorontsov <anton@...msg.org>
To:	Luiz Capitulino <lcapitulino@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, mhocko@...e.cz,
	minchan@...nel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] vmpressure: implement strict mode

On Tue, Jun 25, 2013 at 05:51:29PM -0400, Luiz Capitulino wrote:
> Currently, applications are notified for the level they registered for
> _plus_ higher levels.
> 
> This is a problem if the application wants to implement different
> actions for different levels. For example, an application might want
> to release 10% of its cache on level low, 50% on medium and 100% on
> critical. To do this, the application has to register a different fd
> for each event. However, fd low is always going to be notified and
> and all fds are going to be notified on level critical.
> 
> Strict mode solves this problem by strictly notifiying the event
> an fd has registered for. It's optional. By default we still notify
> on higher levels.
> 
> Signed-off-by: Luiz Capitulino <lcapitulino@...hat.com>

In the documentation I would add more information about why exactly the
strict mode makes sense.

For example, the non-strict fd listener hooked onto the low level makes
sense for apps that just monitor reclaiming activity (like current Android
Activity Manager), hooking onto 'medium' non-strict mode makes sense for
simple load-balancing logic, and the new strict mode is for the cases when
an application wants to implement some fancy logic as it makes a decision
based on a concrete level.

Otherwise, it looks good.

Acked-by: Anton Vorontsov <anton@...msg.org>

Thanks!

Anton
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