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

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Message-ID: <20200813161357.GQ9477@dhcp22.suse.cz>
Date:   Thu, 13 Aug 2020 18:13:57 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     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>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag

On Thu 13-08-20 09:04:42, Paul E. McKenney wrote:
> On Thu, Aug 13, 2020 at 05:54:12PM +0200, Michal Hocko wrote:
[...]
> > If the whole bailout is guarded by CONFIG_PREEMPT_RT specific atomicity
> > check then there is no functional problem - GFP_RT_SAFE would still be
> > GFP_NOWAIT so functional wise the allocator will still do the right
> > thing.
> 
> Perhaps it was just me getting confused, early hour Pacific Time and
> whatever other excuses might apply.  But I thought that you still had
> an objection to GFP_RT_SAFE based on changes in allocator semantics for
> other users.

There is still that problem with lockdep complaining about raw->regular
spinlock on !PREEMPT_RT that would need to get resolved somehow. Thomas
is not really keen on adding some lockdep annotation mechanism and
unfortunatelly I do not have a different idea how to get rid of those.
-- 
Michal Hocko
SUSE Labs