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From: Johannes Weiner <hannes@cmpxchg.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Michal Hocko" <mhocko@kernel.org>,
	"Michal Koutný" <mkoutny@suse.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Vladimir Davydov" <vdavydov.dev@gmail.com>,
	"Waiman Long" <longman@redhat.com>
Subject: Re: [PATCH v2 2/4] mm/memcg: Disable threshold event handlers on PREEMPT_RT
Date: Mon, 14 Feb 2022 11:23:59 -0500	[thread overview]
Message-ID: <YgqCH1CcutS8Z2wU@cmpxchg.org> (raw)
In-Reply-To: <20220211223537.2175879-3-bigeasy@linutronix.de>

On Fri, Feb 11, 2022 at 11:35:35PM +0100, Sebastian Andrzej Siewior wrote:
> During the integration of PREEMPT_RT support, the code flow around
> memcg_check_events() resulted in `twisted code'. Moving the code around
> and avoiding then would then lead to an additional local-irq-save
> section within memcg_check_events(). While looking better, it adds a
> local-irq-save section to code flow which is usually within an
> local-irq-off block on non-PREEMPT_RT configurations.
> 
> The threshold event handler is a deprecated memcg v1 feature. Instead of
> trying to get it to work under PREEMPT_RT just disable it. There should
> be no users on PREEMPT_RT. From that perspective it makes even less
> sense to get it to work under PREEMPT_RT while having zero users.
> 
> Make memory.soft_limit_in_bytes and cgroup.event_control return
> -EOPNOTSUPP on PREEMPT_RT. Make an empty memcg_check_events() and
> memcg_write_event_control() which return only -EOPNOTSUPP on PREEMPT_RT.
> Document that the two knobs are disabled on PREEMPT_RT.
> 
> Suggested-by: Michal Hocko <mhocko@kernel.org>
> Suggested-by: Michal Koutný <mkoutny@suse.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>


WARNING: multiple messages have this Message-ID (diff)
From: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
To: Sebastian Andrzej Siewior
	<bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	"Andrew Morton"
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	"Michal Hocko" <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	"Michal Koutný" <mkoutny-IBi9RG/b67k@public.gmane.org>,
	"Peter Zijlstra" <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	"Thomas Gleixner" <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	"Vladimir Davydov"
	<vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	"Waiman Long" <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH v2 2/4] mm/memcg: Disable threshold event handlers on PREEMPT_RT
Date: Mon, 14 Feb 2022 11:23:59 -0500	[thread overview]
Message-ID: <YgqCH1CcutS8Z2wU@cmpxchg.org> (raw)
In-Reply-To: <20220211223537.2175879-3-bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>

On Fri, Feb 11, 2022 at 11:35:35PM +0100, Sebastian Andrzej Siewior wrote:
> During the integration of PREEMPT_RT support, the code flow around
> memcg_check_events() resulted in `twisted code'. Moving the code around
> and avoiding then would then lead to an additional local-irq-save
> section within memcg_check_events(). While looking better, it adds a
> local-irq-save section to code flow which is usually within an
> local-irq-off block on non-PREEMPT_RT configurations.
> 
> The threshold event handler is a deprecated memcg v1 feature. Instead of
> trying to get it to work under PREEMPT_RT just disable it. There should
> be no users on PREEMPT_RT. From that perspective it makes even less
> sense to get it to work under PREEMPT_RT while having zero users.
> 
> Make memory.soft_limit_in_bytes and cgroup.event_control return
> -EOPNOTSUPP on PREEMPT_RT. Make an empty memcg_check_events() and
> memcg_write_event_control() which return only -EOPNOTSUPP on PREEMPT_RT.
> Document that the two knobs are disabled on PREEMPT_RT.
> 
> Suggested-by: Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Suggested-by: Michal Koutný <mkoutny-IBi9RG/b67k@public.gmane.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>

Acked-by: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>

  reply	other threads:[~2022-02-14 16:24 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-11 22:35 [PATCH v2 0/4] mm/memcg: Address PREEMPT_RT problems instead of disabling it Sebastian Andrzej Siewior
2022-02-11 22:35 ` Sebastian Andrzej Siewior
2022-02-11 22:35 ` [PATCH v2 1/4] mm/memcg: Revert ("mm/memcg: optimize user context object stock access") Sebastian Andrzej Siewior
2022-02-11 22:35   ` Sebastian Andrzej Siewior
2022-02-14 16:23   ` Johannes Weiner
2022-02-14 16:23     ` Johannes Weiner
2022-02-14 19:45   ` Roman Gushchin
2022-02-14 19:45     ` Roman Gushchin
2022-02-11 22:35 ` [PATCH v2 2/4] mm/memcg: Disable threshold event handlers on PREEMPT_RT Sebastian Andrzej Siewior
2022-02-11 22:35   ` Sebastian Andrzej Siewior
2022-02-14 16:23   ` Johannes Weiner [this message]
2022-02-14 16:23     ` Johannes Weiner
2022-02-14 19:46   ` Roman Gushchin
2022-02-14 19:46     ` Roman Gushchin
2022-02-11 22:35 ` [PATCH v2 3/4] mm/memcg: Protect per-CPU counter by disabling preemption on PREEMPT_RT where needed Sebastian Andrzej Siewior
2022-02-11 22:35   ` Sebastian Andrzej Siewior
2022-02-14 16:46   ` Johannes Weiner
2022-02-14 16:46     ` Johannes Weiner
2022-02-14 19:53     ` Roman Gushchin
2022-02-14 19:53       ` Roman Gushchin
2022-02-15 18:01     ` Sebastian Andrzej Siewior
2022-02-15 18:01       ` Sebastian Andrzej Siewior
2022-02-11 22:35 ` [PATCH v2 4/4] mm/memcg: Protect memcg_stock with a local_lock_t Sebastian Andrzej Siewior
2022-02-11 22:35   ` Sebastian Andrzej Siewior
2022-02-14 16:23   ` Johannes Weiner
2022-02-14 16:23     ` Johannes Weiner
2022-02-16 15:51     ` Sebastian Andrzej Siewior
2022-02-16 15:51       ` Sebastian Andrzej Siewior
2022-02-16 18:08       ` Johannes Weiner
2022-02-16 18:08         ` Johannes Weiner
2022-02-17  9:28         ` Sebastian Andrzej Siewior
2022-02-17  9:28           ` Sebastian Andrzej Siewior

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