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

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Message-ID: <20200811102818.GJ4793@dhcp22.suse.cz>
Date:   Tue, 11 Aug 2020 12:28:18 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     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>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        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 11-08-20 11:42:51, Uladzislau Rezki wrote:
> On Tue, Aug 11, 2020 at 11:37:13AM +0200, Uladzislau Rezki wrote:
> > On Tue, Aug 11, 2020 at 10:19:17AM +0200, Michal Hocko wrote:
[...]
> > > Anyway, if the zone->lock is not a good fit for raw_spin_lock then the
> > > only way I can see forward is to detect real (RT) atomic contexts and
> > > bail out early before taking the lock in the allocator for NOWAIT/ATOMIC
> > > requests.
> > >
> This is similar what i have done with mm: Add __GFP_NO_LOCKS flag. I just
> did it for order-0 pages(other paths are impossible) and made it common for
> any kernel.
> 
> Because when you say "bail out early" i suspect that we would like to check
> the per-cpu-list cache.

Bail out early means to do as much as possible until a raw non-compliant
lock has to be taken.

-- 
Michal Hocko
SUSE Labs