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

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Message-ID: <20200813191347.GV9477@dhcp22.suse.cz>
Date:   Thu, 13 Aug 2020 21:13:47 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     peterz@...radead.org
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Uladzislau Rezki <urezki@...il.com>,
        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 Thu 13-08-20 20:31:21, Peter Zijlstra wrote:
> On Thu, Aug 13, 2020 at 09:29:04AM -0700, Paul E. McKenney wrote:
[...]
> > 3.	Reusing existing GFP_ flags/values/whatever to communicate
> > 	the raw-context information that was to be communicated by
> > 	the new GFP_ flag.
> > 
> > 4.	Making lockdep forgive acquiring spinlocks while holding
> > 	raw spinlocks, but only in CONFIG_PREEMPT_NONE=y kernels.
> > 
> > Am I missing anything?
> 
> How would 4 solve anything?

Nothing on its own but along with http://lkml.kernel.org/r/20200813075027.GD9477@dhcp22.suse.cz
it would allow at least _some_ NOWAIT semantic for RT atomic contexts
and prevent from lockdep false positives for !RT trees.
-- 
Michal Hocko
SUSE Labs