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From: Joel Fernandes <joel@joelfernandes.org>
To: Michal Hocko <mhocko@suse.com>
Cc: Uladzislau Rezki <urezki@gmail.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	 "Paul E. McKenney" <paulmck@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,  RCU <rcu@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	 Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	 Vlastimil Babka <vbabka@suse.cz>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Theodore Y . Ts'o" <tytso@mit.edu>,
	 Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	 Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>,
	Mel Gorman <mgorman@suse.de>
Subject: Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func.
Date: Wed, 30 Sep 2020 13:48:40 -0400	[thread overview]
Message-ID: <CAEXW_YSvnC+hv2Y47Nrg5TS1gZ8UPnSBooqMv7krcrxe94EWSQ@mail.gmail.com> (raw)
In-Reply-To: <20200930172205.GY2277@dhcp22.suse.cz>

On Wed, Sep 30, 2020 at 1:22 PM Michal Hocko <mhocko@suse.com> wrote:

> > > > I think documenting is useful.
> > > >
> > > > Could it be more explicit in what the issue is? Something like:
> > > >
> > > > * Even with GFP_ATOMIC, calls to the allocator can sleep on PREEMPT_RT
> > > > systems. Therefore, the current low-level allocator implementation does not
> > > > support being called from special contexts that are atomic on RT - such as
> > > > NMI and raw_spin_lock. Due to these constraints and considering calling code
> > > > usually has no control over the PREEMPT_RT configuration, callers of the
> > > > allocator should avoid calling the allocator from these cotnexts even in
> > > > non-RT systems.
> > >
> > > I do not mind documenting RT specific behavior but as mentioned in other
> > > reply, this should likely go via RT tree for now. There is likely more
> > > to clarify about atomicity for PREEMPT_RT.
> >
> > I am sorry, I did not understand what you meant by something missing
> > in Linus Tree. CONFIG_PREEMPT_RT is there.
>
> OK, I was not aware we already CONFIG_PREEMPT_RT in the three. There is
> still a lot from the RT patchset including sleeping spin locks that make
> a real difference. Or maybe I haven't checked properly.
>
> > Could you clarify? Also the CONFIG_PREEMPT_RT is the only thing
> > driving this requirement for GFP_ATOMIC right? Or are there non-RT
> > reasons why GFP_ATOMIC allocation cannot be done from
> > NMI/raw_spin_lock ?
>
> I have already sent a clarification patch [1]. NMI is not supported
> regardless of the preemption mode. Hope this clarifies it a bit.
>
> [1] http://lkml.kernel.org/r/20200929123010.5137-1-mhocko@kernel.org

That works for me. Thanks,

  - Joel


  reply	other threads:[~2020-09-30 17:48 UTC|newest]

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-18 19:48 [PATCH 0/4] kvfree_rcu() and _LOCK_NESTING/_PREEMPT_RT Uladzislau Rezki (Sony)
2020-09-18 19:48 ` [PATCH 1/4] rcu/tree: Add a work to allocate pages from regular context Uladzislau Rezki (Sony)
2020-09-18 19:48 ` [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func Uladzislau Rezki (Sony)
2020-09-21  7:47   ` Michal Hocko
2020-09-21 15:45     ` Paul E. McKenney
2020-09-21 16:03       ` Michal Hocko
2020-09-21 19:48         ` Uladzislau Rezki
2020-09-22  7:50           ` Michal Hocko
2020-09-22 13:12             ` Uladzislau Rezki
2020-09-22 15:35               ` Michal Hocko
2020-09-23 10:37               ` Mel Gorman
2020-09-23 15:41                 ` Paul E. McKenney
2020-09-23 23:22                   ` Mel Gorman
2020-09-24  8:16                     ` Uladzislau Rezki
2020-09-24 11:16                       ` Peter Zijlstra
2020-09-24 15:16                         ` Uladzislau Rezki
2020-09-24 11:19                       ` Peter Zijlstra
2020-09-24 15:21                         ` Uladzislau Rezki
2020-09-25  8:15                           ` Peter Zijlstra
2020-09-25 10:25                             ` Uladzislau Rezki
2020-09-24 15:38                         ` Paul E. McKenney
2020-09-25  8:26                           ` Peter Zijlstra
2020-09-26 14:37                             ` Paul E. McKenney
2020-09-25  8:05                       ` Michal Hocko
2020-09-25 15:31                         ` Uladzislau Rezki
2020-09-25 15:47                           ` Michal Hocko
2020-09-29 16:25                             ` Uladzislau Rezki
2020-09-30  9:27                               ` Michal Hocko
2020-09-30 12:35                                 ` Uladzislau Rezki
2020-09-30 12:44                                   ` Michal Hocko
2020-09-30 13:39                                     ` Uladzislau Rezki
2020-09-30 16:46                                       ` Michal Hocko
2020-09-30 20:36                                         ` Uladzislau Rezki
2020-09-30 15:25                             ` Joel Fernandes
2020-09-30 16:48                               ` Michal Hocko
2020-09-30 17:03                                 ` Joel Fernandes
2020-09-30 17:22                                   ` Michal Hocko
2020-09-30 17:48                                     ` Joel Fernandes [this message]
2020-09-25 16:17                           ` Mel Gorman
2020-09-25 17:57                             ` Uladzislau Rezki
2020-09-22 15:49             ` Paul E. McKenney
2020-09-22  3:35         ` Paul E. McKenney
2020-09-22  8:03           ` Michal Hocko
2020-09-22 15:46             ` Paul E. McKenney
2020-09-23 11:27               ` Uladzislau Rezki
2020-09-29 10:15   ` Vlastimil Babka
2020-09-29 22:07     ` Uladzislau Rezki
2020-09-30 10:35       ` Michal Hocko
2020-10-01 19:32         ` Uladzislau Rezki
2020-09-30 14:39       ` Vlastimil Babka
2020-09-30 15:37         ` Joel Fernandes
2020-10-01 19:26         ` Uladzislau Rezki
2020-10-02  7:11           ` Michal Hocko
2020-10-02  8:50             ` Mel Gorman
2020-10-02  9:05               ` Michal Hocko
2020-10-05 15:08                 ` Uladzislau Rezki
2020-10-05 15:41                   ` Michal Hocko
2020-10-06 22:25                     ` Uladzislau Rezki
2020-10-07 10:02                       ` Michal Hocko
2020-10-07 11:02                         ` Uladzislau Rezki
2020-10-02  9:07               ` Peter Zijlstra
2020-10-02  9:45                 ` Mel Gorman
2020-10-02  9:58                   ` Peter Zijlstra
2020-10-02 10:19                     ` Mel Gorman
2020-10-02 14:41                       ` Paul E. McKenney
2020-10-06 10:03                         ` Mel Gorman
2020-10-06 15:41                           ` Paul E. McKenney
2020-10-05 13:58             ` Uladzislau Rezki
2020-10-02  8:06           ` Mel Gorman
2020-10-05 14:12             ` Uladzislau Rezki
2020-09-18 19:48 ` [PATCH 3/4] rcu/tree: use " Uladzislau Rezki (Sony)
2020-09-18 19:48 ` [PATCH 4/4] rcu/tree: Use schedule_delayed_work() instead of WQ_HIGHPRI queue Uladzislau Rezki (Sony)
2020-09-20 15:06   ` Paul E. McKenney
2020-09-21 13:27     ` Uladzislau Rezki
2020-09-18 22:15 ` [PATCH 0/4] kvfree_rcu() and _LOCK_NESTING/_PREEMPT_RT Paul E. McKenney
2020-09-30 15:52 ` Joel Fernandes

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