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From: Simon Jeons <simon.jeons@gmail.com>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Petr Holasek <pholasek@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Izik Eidus <izik.eidus@ravellosystems.com>,
	Rik van Riel <riel@redhat.com>,
	David Rientjes <rientjes@google.com>,
	Anton Arapov <anton@redhat.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 1/11] ksm: allow trees per NUMA node
Date: Sat, 26 Jan 2013 21:16:21 -0600	[thread overview]
Message-ID: <1359256581.4159.16.camel@kernel> (raw)
In-Reply-To: <alpine.LNX.2.00.1301261826000.7411@eggly.anvils>

On Sat, 2013-01-26 at 18:54 -0800, Hugh Dickins wrote:
> On Sat, 26 Jan 2013, Simon Jeons wrote:
> > On Fri, 2013-01-25 at 17:54 -0800, Hugh Dickins wrote:
> > > From: Petr Holasek <pholasek@redhat.com>
> > > @@ -1122,6 +1166,18 @@ struct rmap_item *unstable_tree_search_i
> > >  			return NULL;
> > >  		}
> > >  
> > > +		/*
> > > +		 * If tree_page has been migrated to another NUMA node, it
> > > +		 * will be flushed out and put into the right unstable tree
> > 
> > Then why not insert the new page to unstable tree during page migration
> > against current upstream? Because default behavior is merge across
> > nodes.
> 
> I don't understand the words "against current upstream" in your question.

I mean current upstream codes without numa awareness. :)

> 
> We cannot move a page (strictly, a node) from one tree to another during
> page migration itself, because the necessary ksm_thread_mutex is not held.
> Not would we even want to while "merge across nodes".
> 
> Ah, perhaps you are pointing out that in current upstream, the only user
> of ksm page migration is memory hotremove, which in current upstream does
> hold ksm_thread_mutex.
> 
> So you'd like us to add code for moving a node from one tree to another
> in ksm_migrate_page() (and what would it do when it collides with an

Without numa awareness, I still can't understand your explanation why
can't insert the node to the tree just after page migration instead of
inserting it at the next scan.

> existing node?), code which will then be removed a few patches later
> when ksm page migration is fully enabled?
> 
> No, I'm not going to put any more thought into that.  When Andrea pointed
> out the problem with Petr's original change to ksm_migrate_page(), I did
> indeed think that we could do something cleverer at that point; but once
> I got down to trying it, found that a dead end.  I wasn't going to be
> able to test the hotremove case properly anyway, so no good pursuing
> solutions that couldn't be generalized.
> 
> Hugh


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  reply	other threads:[~2013-01-27  3:16 UTC|newest]

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-26  1:53 [PATCH 0/11] ksm: NUMA trees and page migration Hugh Dickins
2013-01-26  1:54 ` [PATCH 1/11] ksm: allow trees per NUMA node Hugh Dickins
2013-01-27  1:14   ` Simon Jeons
2013-01-27  2:54     ` Hugh Dickins
2013-01-27  3:16       ` Simon Jeons [this message]
2013-01-27 21:55         ` Hugh Dickins
2013-01-28 23:03   ` Andrew Morton
2013-01-29  1:17     ` Hugh Dickins
2013-01-28 23:08   ` Andrew Morton
2013-01-29  1:38     ` Hugh Dickins
2013-02-05 16:41   ` Mel Gorman
2013-02-07 23:57     ` Hugh Dickins
2013-01-26  1:56 ` [PATCH 2/11] ksm: add sysfs ABI Documentation Hugh Dickins
2013-01-26  1:58 ` [PATCH 3/11] ksm: trivial tidyups Hugh Dickins
2013-01-28 23:11   ` Andrew Morton
2013-01-29  1:44     ` Hugh Dickins
2013-01-26  1:59 ` [PATCH 4/11] ksm: reorganize ksm_check_stable_tree Hugh Dickins
2013-02-05 16:48   ` Mel Gorman
2013-02-08  0:07     ` Hugh Dickins
2013-02-14 11:30       ` Mel Gorman
2013-01-26  2:00 ` [PATCH 5/11] ksm: get_ksm_page locked Hugh Dickins
2013-01-27  2:36   ` Simon Jeons
2013-01-27 22:08     ` Hugh Dickins
2013-01-28  0:36       ` Simon Jeons
2013-01-28  3:35         ` Hugh Dickins
2013-01-27  2:48   ` Simon Jeons
2013-01-27 22:10     ` Hugh Dickins
2013-02-05 17:18   ` Mel Gorman
2013-02-08  0:33     ` Hugh Dickins
2013-02-14 11:34       ` Mel Gorman
2013-01-26  2:01 ` [PATCH 6/11] ksm: remove old stable nodes more thoroughly Hugh Dickins
2013-01-27  4:55   ` Simon Jeons
2013-01-27 23:05     ` Hugh Dickins
2013-01-28  1:42       ` Simon Jeons
2013-01-28  4:14         ` Hugh Dickins
2013-01-28  2:12   ` Simon Jeons
2013-01-28  4:19     ` Hugh Dickins
2013-01-28  6:36   ` Simon Jeons
2013-01-28 23:44   ` Andrew Morton
2013-01-29  2:03     ` Hugh Dickins
2013-02-05 17:55   ` Mel Gorman
2013-02-08 19:33     ` Hugh Dickins
2013-02-14 11:58       ` Mel Gorman
2013-02-14 22:19         ` Hugh Dickins
2013-01-26  2:03 ` [PATCH 7/11] ksm: make KSM page migration possible Hugh Dickins
2013-01-27  5:47   ` Simon Jeons
2013-01-27 23:12     ` Hugh Dickins
2013-01-28  0:41       ` Simon Jeons
2013-01-28  3:44         ` Hugh Dickins
2013-02-05 19:11   ` Mel Gorman
2013-02-08 20:52     ` Hugh Dickins
2013-01-26  2:05 ` [PATCH 8/11] ksm: make !merge_across_nodes migration safe Hugh Dickins
2013-01-27  8:49   ` Simon Jeons
2013-01-27 23:25     ` Hugh Dickins
2013-01-28  3:44   ` Simon Jeons
2013-01-26  2:06 ` [PATCH 9/11] ksm: enable KSM page migration Hugh Dickins
2013-01-26  2:07 ` [PATCH 10/11] mm: remove offlining arg to migrate_pages Hugh Dickins
2013-01-26  2:10 ` [PATCH 11/11] ksm: stop hotremove lockdep warning Hugh Dickins
2013-01-27  6:23   ` Simon Jeons
2013-01-27 23:35     ` Hugh Dickins
2013-02-08 18:45   ` Gerald Schaefer
2013-02-11 22:13     ` Hugh Dickins
2013-01-28 23:54 ` [PATCH 0/11] ksm: NUMA trees and page migration Andrew Morton
2013-01-29  0:49   ` Izik Eidus
2013-01-29  2:26     ` Izik Eidus
2013-01-29 16:51       ` Andrea Arcangeli
2013-01-31  0:05         ` Ric Mason
2013-01-29  1:07   ` Hugh Dickins
2013-01-29 10:45     ` Gleb Natapov

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