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From: Michal Hocko <mhocko@kernel.org>
To: Mel Gorman <mgorman@suse.de>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>,
	David Nellans <dnellans@nvidia.com>,
	Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, vbabka@suse.cz,
	minchan@kernel.org, aneesh.kumar@linux.vnet.ibm.com,
	bsingharora@gmail.com, srikar@linux.vnet.ibm.com,
	haren@linux.vnet.ibm.com, jglisse@redhat.com,
	dave.hansen@intel.com, dan.j.williams@intel.com,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH 0/6] Enable parallel page migration
Date: Fri, 10 Mar 2017 15:45:39 +0100	[thread overview]
Message-ID: <20170310144539.GK3753@dhcp22.suse.cz> (raw)
In-Reply-To: <20170310140715.z6ostiatqx5oiu2i@suse.de>

On Fri 10-03-17 14:07:16, Mel Gorman wrote:
> On Thu, Mar 09, 2017 at 05:46:16PM -0600, Zi Yan wrote:
[...]
> > I understand your concern on CPU utilization impact. I think checking
> > CPU utilization and only using idle CPUs could potentially avoid this
> > problem.
> > 
> 
> That will be costly to detect actually. It would require poking into the
> scheduler core and incurring a number of cache misses for a race-prone
> operation that may not succeed. Even if you do it, it'll still be
> brought up that the serialised case should be optimised first.

do not forget that seeing idle cpus is not a sufficient criterion to use
it for parallel migration. There might be other policies you are not
aware of from the MM code to keep them idle (power saving and who knows
what else). Developing a reasonable strategy for spreading the load to
different CPUs is really hard, much harder than you can imaging I
suspect (just look at how hard it was and I long it took to get to a
reasonable scheduler driven frequency scaling/power governors).
-- 
Michal Hocko
SUSE Labs

WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org>
To: Mel Gorman <mgorman@suse.de>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>,
	David Nellans <dnellans@nvidia.com>,
	Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, vbabka@suse.cz,
	minchan@kernel.org, aneesh.kumar@linux.vnet.ibm.com,
	bsingharora@gmail.com, srikar@linux.vnet.ibm.com,
	haren@linux.vnet.ibm.com, jglisse@redhat.com,
	dave.hansen@intel.com, dan.j.williams@intel.com,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH 0/6] Enable parallel page migration
Date: Fri, 10 Mar 2017 15:45:39 +0100	[thread overview]
Message-ID: <20170310144539.GK3753@dhcp22.suse.cz> (raw)
In-Reply-To: <20170310140715.z6ostiatqx5oiu2i@suse.de>

On Fri 10-03-17 14:07:16, Mel Gorman wrote:
> On Thu, Mar 09, 2017 at 05:46:16PM -0600, Zi Yan wrote:
[...]
> > I understand your concern on CPU utilization impact. I think checking
> > CPU utilization and only using idle CPUs could potentially avoid this
> > problem.
> > 
> 
> That will be costly to detect actually. It would require poking into the
> scheduler core and incurring a number of cache misses for a race-prone
> operation that may not succeed. Even if you do it, it'll still be
> brought up that the serialised case should be optimised first.

do not forget that seeing idle cpus is not a sufficient criterion to use
it for parallel migration. There might be other policies you are not
aware of from the MM code to keep them idle (power saving and who knows
what else). Developing a reasonable strategy for spreading the load to
different CPUs is really hard, much harder than you can imaging I
suspect (just look at how hard it was and I long it took to get to a
reasonable scheduler driven frequency scaling/power governors).
-- 
Michal Hocko
SUSE Labs

--
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  reply	other threads:[~2017-03-10 14:45 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-17 11:24 [PATCH 0/6] Enable parallel page migration Anshuman Khandual
2017-02-17 11:24 ` Anshuman Khandual
2017-02-17 11:24 ` [PATCH 1/6] mm/migrate: Add new mode parameter to migrate_page_copy() function Anshuman Khandual
2017-02-17 11:24   ` Anshuman Khandual
2017-03-09  6:24   ` Anshuman Khandual
2017-03-09  6:24     ` Anshuman Khandual
2017-02-17 11:24 ` [PATCH 2/6] mm/migrate: Make migrate_mode types non-exclusive Anshuman Khandual
2017-02-17 11:24   ` Anshuman Khandual
2017-02-17 11:24 ` [PATCH 3/6] mm/migrate: Add copy_pages_mthread function Anshuman Khandual
2017-02-17 11:24   ` Anshuman Khandual
2017-02-17 12:27   ` kbuild test robot
2017-03-08 15:40     ` Anshuman Khandual
2017-03-08 15:40       ` Anshuman Khandual
2017-03-09  6:25   ` Anshuman Khandual
2017-03-09  6:25     ` Anshuman Khandual
2017-02-17 11:24 ` [PATCH 4/6] mm/migrate: Add new migrate mode MIGRATE_MT Anshuman Khandual
2017-02-17 11:24   ` Anshuman Khandual
2017-02-17 11:24 ` [PATCH 5/6] mm/migrate: Add new migration flag MPOL_MF_MOVE_MT for syscalls Anshuman Khandual
2017-02-17 11:24   ` Anshuman Khandual
2017-03-09  6:26   ` Anshuman Khandual
2017-03-09  6:26     ` Anshuman Khandual
2017-02-17 11:24 ` [PATCH 6/6] sysctl: Add global tunable mt_page_copy Anshuman Khandual
2017-02-17 11:24   ` Anshuman Khandual
2017-02-17 15:30   ` kbuild test robot
2017-03-08 15:37     ` Anshuman Khandual
2017-03-08 15:37       ` Anshuman Khandual
2017-03-10  1:12       ` [kbuild-all] " Ye Xiaolong
2017-03-10  1:12         ` Ye Xiaolong
2017-03-10 12:11         ` Anshuman Khandual
2017-03-10 12:11           ` Anshuman Khandual
2017-02-22  5:04 ` [PATCH 0/6] Enable parallel page migration Balbir Singh
2017-02-22  5:04   ` Balbir Singh
2017-02-22  5:55   ` Anshuman Khandual
2017-02-22  5:55     ` Anshuman Khandual
2017-02-22 10:52     ` Balbir Singh
2017-02-22 10:52       ` Balbir Singh
2017-03-08 16:04 ` Anshuman Khandual
2017-03-08 16:04   ` Anshuman Khandual
2017-03-09 15:09   ` Mel Gorman
2017-03-09 15:09     ` Mel Gorman
2017-03-09 17:38     ` David Nellans
2017-03-09 17:38       ` David Nellans
2017-03-09 22:15       ` Mel Gorman
2017-03-09 22:15         ` Mel Gorman
2017-03-09 23:46         ` Zi Yan
2017-03-09 23:46           ` Zi Yan
2017-03-10 14:07           ` Mel Gorman
2017-03-10 14:07             ` Mel Gorman
2017-03-10 14:45             ` Michal Hocko [this message]
2017-03-10 14:45               ` Michal Hocko
2017-03-10 13:05     ` Michal Hocko
2017-03-10 13:05       ` Michal Hocko

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