From: Mel Gorman <mgorman@suse.de>
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>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 4/11] ksm: reorganize ksm_check_stable_tree
Date: Thu, 14 Feb 2013 11:30:05 +0000 [thread overview]
Message-ID: <20130214113005.GA7367@suse.de> (raw)
In-Reply-To: <alpine.LNX.2.00.1302071558100.2133@eggly.anvils>
On Thu, Feb 07, 2013 at 04:07:17PM -0800, Hugh Dickins wrote:
> On Tue, 5 Feb 2013, Mel Gorman wrote:
> > On Fri, Jan 25, 2013 at 05:59:35PM -0800, Hugh Dickins wrote:
> > > Memory hotremove's ksm_check_stable_tree() is pitifully inefficient
> > > (restarting whenever it finds a stale node to remove), but rearrange
> > > so that at least it does not needlessly restart from nid 0 each time.
> > > And add a couple of comments: here is why we keep pfn instead of page.
> > >
> > > Signed-off-by: Hugh Dickins <hughd@google.com>
> > > ---
> > > mm/ksm.c | 38 ++++++++++++++++++++++----------------
> > > 1 file changed, 22 insertions(+), 16 deletions(-)
> > >
> > > --- mmotm.orig/mm/ksm.c 2013-01-25 14:36:52.152205940 -0800
> > > +++ mmotm/mm/ksm.c 2013-01-25 14:36:53.244205966 -0800
> > > @@ -1830,31 +1830,36 @@ void ksm_migrate_page(struct page *newpa
> > > #endif /* CONFIG_MIGRATION */
> > >
> > > #ifdef CONFIG_MEMORY_HOTREMOVE
> > > -static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
> > > - unsigned long end_pfn)
> > > +static void ksm_check_stable_tree(unsigned long start_pfn,
> > > + unsigned long end_pfn)
> > > {
> > > + struct stable_node *stable_node;
> > > struct rb_node *node;
> > > int nid;
> > >
> > > - for (nid = 0; nid < nr_node_ids; nid++)
> > > - for (node = rb_first(&root_stable_tree[nid]); node;
> > > - node = rb_next(node)) {
> > > - struct stable_node *stable_node;
> > > -
> > > + for (nid = 0; nid < nr_node_ids; nid++) {
> > > + node = rb_first(&root_stable_tree[nid]);
> > > + while (node) {
> >
> > This is not your fault, the old code is wrong too. It is assuming that all
> > nodes are populated in numeric orders with no holes. It won't work if just
> > two nodes 0 and 4 are online. It should be using for_each_online_node().
>
> If the old code is wrong, it probably would be my fault! But I believe
> this is okay: these rb_roots we're looking at, they are in memory which
> is not being offlined, and the trees for offline nodes will simply be
> empty, won't they? Something's badly wrong if otherwise.
>
I would expect them to be empty but that was not the problem I had in
mind. Unfortunately I mixed up nr_online_ids and nr_node_ids and read
the loop incorrectly. What you have is fine.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2013-02-14 11:30 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
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 [this message]
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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