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 <[email protected]> > > --- > > 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 certainly prefer to avoid for_each_online_node() etc: maybe I'm confusing with for_each_online_something_else(), but experience tells that you can get into nasty hotplug mutex ordering issues with those things - not worth the pain if you can easily and safely avoid them. Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
