linux-kernel - Re: [PATCH v2] vmpressure: implement strict mode

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 28 Jun 2013 15:44:02 -0400
From:	Luiz Capitulino <lcapitulino@...hat.com>
To:	Anton Vorontsov <anton@...msg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mhocko@...e.cz, kmpark@...radead.org,
	hyunhee.kim@...sung.com
Subject: Re: [PATCH v2] vmpressure: implement strict mode

On Fri, 28 Jun 2013 11:55:47 -0700
Anton Vorontsov <anton@...msg.org> wrote:

> On Fri, Jun 28, 2013 at 02:45:07PM -0400, Luiz Capitulino wrote:
> > On Fri, 28 Jun 2013 10:09:17 -0700
> > Anton Vorontsov <anton@...msg.org> wrote:
> > 
> > > So, I would now argue that the current scheme is perfectly OK and can do
> > > everything you can do with the "strict" one,
> > 
> > I forgot commenting this bit. This is not true, because I don't want a
> > low fd to be notified on critical level. The current interface just
> > can't do that.
> 
> Why can't you use poll() and demultiplex the events? Check if there is an
> event in the crit fd, and if there is, then just ignore all the rest.

This may be a valid workaround for current kernels, but application
behavior will be different among kernels with a different number of
events.

Say, we events on top of critical. Then crit fd will now be
notified for cases where it didn't use to on older kernels.

> > However, it *is* possible to make non-strict work on strict if we make
> > strict default _and_ make reads on memory.pressure_level return
> > available events. Just do this on app initialization:
> > 
> > for each event in memory.pressure_level; do
> > 	/* register eventfd to be notified on "event" */
> > done
> 
> This scheme registers "all" events.

Yes, because I thought that's the user-case that matters for activity
manager :)

> Here is more complicated case:
> 
> Old kernels, pressure_level reads:
> 
>   low, med, crit
> 
> The app just wants to listen for med level.
> 
> New kernels, pressure_level reads:
> 
>   low, FOO, med, BAR, crit
> 
> How would application decide which of FOO and BAR are ex-med levels?

What you meant by ex-med?

Let's not over-design. I agree that allowing the API to be extended
is a good thing, but we shouldn't give complex meaning to events,
otherwise we're better with a numeric scale instead.
--
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/