linux-kernel - Re: [RFC-PATCH 1/2] mm: Add __GFP_NO

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]

Message-ID: <20200818161355.GE27891@paulmck-ThinkPad-P72>
Date:   Tue, 18 Aug 2020 09:13:55 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Michal Hocko <mhocko@...e.com>,
        Uladzislau Rezki <urezki@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Joel Fernandes <joel@...lfernandes.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag

On Tue, Aug 18, 2020 at 04:43:14PM +0200, Thomas Gleixner wrote:
> On Tue, Aug 18 2020 at 06:53, Paul E. McKenney wrote:
> > On Tue, Aug 18, 2020 at 09:43:44AM +0200, Michal Hocko wrote:
> >> Thomas had a good point that it doesn't really make much sense to
> >> optimize for flooders because that just makes them more effective.
> >
> > The point is not to make the flooders go faster, but rather for the
> > system to be robust in the face of flooders.  Robust as in harder for
> > a flooder to OOM the system.
> >
> > And reducing the number of post-grace-period cache misses makes it
> > easier for the callback-invocation-time memory freeing to keep up with
> > the flooder, thus avoiding (or at least delaying) the OOM.
> 
> Throttling the flooder is incresing robustness far more than reducing
> cache misses.

True, but it takes time to identify a flooding event that needs to be
throttled (as in milliseconds).  This time cannot be made up.

And in the absence of a flooding event, the last thing you want to do
is to throttle call_rcu(), kfree_rcu(), and kvfree_rcu().

							Thanx, Paul