Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
From: Vlastimil Babka <vbabka@suse.cz>
To: Christopher Lameter <cl@linux.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	David Rientjes <rientjes@google.com>,
	Pekka Enberg <penberg@kernel.org>, Tejun Heo <tj@kernel.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	John Stultz <john.stultz@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Stephen Boyd <sboyd@kernel.org>
Subject: Re: [RFC] mm, slab: reschedule cache_reap() on the same CPU
Date: Tue, 10 Apr 2018 21:40:19 +0200
Message-ID: <983c61d1-1444-db1f-65c1-3b519ac4d57b@suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.20.1804100907160.27333@nuc-kabylake>

On 04/10/2018 04:12 PM, Christopher Lameter wrote:
> On Tue, 10 Apr 2018, Vlastimil Babka wrote:
> 
>> cache_reap() is initially scheduled in start_cpu_timer() via
>> schedule_delayed_work_on(). But then the next iterations are scheduled via
>> schedule_delayed_work(), thus using WORK_CPU_UNBOUND.
> 
> That is a bug.. cache_reap must run on the same cpu since it deals with
> the per cpu queues of the current cpu. Scheduled_delayed_work() used to
> guarantee running on teh same cpu.

Did it? When did it stop? (which stable kernels should we backport to?)
So is my assumption correct that without specifying a CPU, the next work
might be processed on a different cpu than the current one, *and also*
be executed with a kthread/u* that can migrate to another cpu *in the
middle of the work*? Tejun?

>> This patch makes sure schedule_delayed_work_on() is used with the proper cpu
>> when scheduling the next iteration. The cpu is stored with delayed_work on a
>> new slab_reap_work_struct super-structure.
> 
> The current cpu is readily available via smp_processor_id(). Why a
> super structure?

Mostly for the WARN_ON_ONCE, and general paranoia.

>> @@ -4074,7 +4086,8 @@ static void cache_reap(struct work_struct *w)
>>  	next_reap_node();
>>  out:
>>  	/* Set up the next iteration */
>> -	schedule_delayed_work(work, round_jiffies_relative(REAPTIMEOUT_AC));
>> +	schedule_delayed_work_on(reap_work->cpu, work,
>> +					round_jiffies_relative(REAPTIMEOUT_AC));
> 
> schedule_delayed_work_on(smp_processor_id(), work, round_jiffies_relative(REAPTIMEOUT_AC));
> 
> instead all of the other changes?

If we can rely on that 100%, sure.

  parent reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-10  8:15 Vlastimil Babka
2018-04-10 14:12 ` Christopher Lameter
2018-04-10 14:17   ` Tejun Heo
2018-04-10 19:40   ` Vlastimil Babka [this message]
2018-04-10 19:53     ` Tejun Heo
2018-04-10 20:13       ` Vlastimil Babka
2018-04-10 20:23         ` Tejun Heo
2018-04-11  7:00 ` [PATCH] " Vlastimil Babka
2018-04-11 10:53   ` Pekka Enberg
2018-04-11 13:41     ` Christopher Lameter
2018-04-12  0:47   ` Minchan Kim
2018-04-13  8:44     ` Vlastimil Babka

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=983c61d1-1444-db1f-65c1-3b519ac4d57b@suse.cz \
    --to=vbabka@suse.cz \
    --cc=cl@linux.com \
    --cc=iamjoonsoo.kim@lge.com \
    --cc=jiangshanlai@gmail.com \
    --cc=john.stultz@linaro.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=penberg@kernel.org \
    --cc=rientjes@google.com \
    --cc=sboyd@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=tj@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org
	public-inbox-index linux-mm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git