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From: Michal Hocko <mhocko@kernel.org>
To: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Reza Arbab <arbab@linux.vnet.ibm.com>,
	Yasuaki Ishimatsu <yasu.isimatu@gmail.com>,
	qiuxishi@huawei.com, Igor Mammedov <imammedo@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early
Date: Tue, 5 Sep 2017 09:13:07 +0200
Message-ID: <20170905071307.7aggprk66r3cem4p@dhcp22.suse.cz> (raw)
In-Reply-To: <b8e8ffdf-4f7b-2a02-5869-53b23da645d0@linux.vnet.ibm.com>

On Tue 05-09-17 11:59:36, Anshuman Khandual wrote:
[...]
> > @@ -1634,43 +1634,25 @@ static int __ref __offline_pages(unsigned long start_pfn,
> >  
> >  	pfn = start_pfn;
> >  	expire = jiffies + timeout;
> > -	drain = 0;
> > -	retry_max = 5;
> >  repeat:
> >  	/* start memory hot removal */
> > -	ret = -EAGAIN;
> > +	ret = -EBUSY;
> >  	if (time_after(jiffies, expire))
> >  		goto failed_removal;
> >  	ret = -EINTR;
> >  	if (signal_pending(current))
> >  		goto failed_removal;
> > -	ret = 0;
> > -	if (drain) {
> > -		lru_add_drain_all_cpuslocked();
> > -		cond_resched();
> > -		drain_all_pages(zone);
> > -	}
> 
> Why we had this condition before that only when we fail in migration
> later in do_migrate_range function, drain the lru lists in the next
> attempt. Why not from the first attempt itself ? Just being curious.
 
I can only guess but draining used to invoke IPIs and that is really
costly so an optimistic attempt could try without draining and do that
only if the migration fails. Now that we have it all done in WQ context
there shouldn't be any reason to optimize for draining.
-- 
Michal Hocko
SUSE Labs

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Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-04  8:21 [PATCH 0/2] mm, memory_hotplug: redefine memory offline retry logic Michal Hocko
2017-09-04  8:21 ` [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early Michal Hocko
2017-09-05  6:29   ` Anshuman Khandual
2017-09-05  7:13     ` Michal Hocko [this message]
2017-09-08 17:26   ` Vlastimil Babka
2017-09-11  8:17     ` Michal Hocko
2017-09-13 11:41       ` Vlastimil Babka
2017-09-13 12:10         ` Michal Hocko
2017-09-13 12:14           ` Michal Hocko
2017-09-13 12:19             ` Vlastimil Babka
2017-09-13 12:32               ` Michal Hocko
2017-09-04  8:21 ` [PATCH 2/2] mm, memory_hotplug: remove timeout from __offline_memory Michal Hocko
2017-09-04  8:58   ` Xishi Qiu
2017-09-04  9:01     ` Michal Hocko
2017-09-04  9:05       ` Xishi Qiu
2017-09-04  9:15         ` Michal Hocko
2017-09-05  5:46           ` Anshuman Khandual
2017-09-05  7:23             ` Michal Hocko
2017-09-05  8:54               ` Anshuman Khandual
2017-09-08 17:27   ` Vlastimil Babka
2017-09-18  7:08 [PATCH v2 0/2] mm, memory_hotplug: redefine memory offline retry logic Michal Hocko
2017-09-18  7:08 ` [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early Michal Hocko
2017-10-10 12:05   ` Michael Ellerman
2017-10-10 12:27     ` Michal Hocko
2017-10-11  2:37       ` Michael Ellerman
2017-10-11  5:19         ` Michael Ellerman
2017-10-11 14:05           ` Anshuman Khandual
2017-10-11 14:16             ` Michal Hocko
2017-10-11  6:51         ` Michal Hocko
2017-10-11  8:04           ` Vlastimil Babka
2017-10-11  8:13             ` Michal Hocko
2017-10-11 11:17               ` Vlastimil Babka
2017-10-11 11:24                 ` Michal Hocko
2017-10-13 11:42             ` Michael Ellerman
2017-10-13 11:58               ` Michal Hocko

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