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From: Vlastimil Babka <vbabka@suse.cz>
To: Thomas Gleixner <tglx@linutronix.de>,
	Waiman Long <longman@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Roman Gushchin <guro@fb.com>
Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	linux-mm@kvack.org, Shakeel Butt <shakeelb@google.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Luis Goncalves <lgoncalv@redhat.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] mm/memcg: Disable task obj_stock for PREEMPT_RT
Date: Wed, 4 Aug 2021 09:39:23 +0200	[thread overview]
Message-ID: <93dfe0d4-c687-93f8-da75-c5d3c9bd0ac7@suse.cz> (raw)
In-Reply-To: <87h7g62jxm.ffs@tglx>

On 8/4/21 1:21 AM, Thomas Gleixner wrote:
> 	/*
> 	 * The only protection from memory hotplug vs. drain_stock races is
> 	 * that we always operate on local CPU stock here with IRQ disabled
> 	 */
> -	local_irq_save(flags);
> +	local_lock_irqsave(memcg_stock_lock, flags);
>         ...
> 	if (use_task_obj_stock())
>   		drain_obj_stock(&stock->task_obj);
> 
> which is incomprehensible garbage.
> 
> The comment above the existing local_irq_save() is garbage w/o any local
> lock conversion already today (and even before the commit which
> introduced stock::task_obj) simply because that comment does not explain
> the why.

Michal, this seems to be your comment from commit 72f0184c8a00 ("mm, memcg:
remove hotplug locking from try_charge"). Was "memory hotplug" a mistake,
because the rest of the commit is about cpu hotplug, and I don't really see a
memory hotplug connection there?

  parent reply	other threads:[~2021-08-04  7:39 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03 17:55 Waiman Long
2021-08-03 23:21 ` Thomas Gleixner
2021-08-04  1:40   ` Waiman Long
2021-08-04  8:52     ` Michal Hocko
2021-08-04 16:00     ` Waiman Long
2021-08-04  7:39   ` Vlastimil Babka [this message]
2021-08-04  8:33     ` Michal Hocko
2021-08-09  9:07       ` Michal Hocko
2021-08-09  9:28         ` Vlastimil Babka

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