On Wed, 15 Dec 2010 10:25:51 +0100 Ingo Korb <ingo@xxxxxxxx> wrote: > On 15.12.2010 01:21, KAMEZAWA Hiroyuki wrote: > > > It's designed for offline memory section> MAX_ORDER. pageblock_nr_pages > > is tend to be smaller than that. > > > > Do you see the problem with _exsisting_ user interface of memory hotplug ? > > I think we have no control other than memory section. > > The existing, exported interface (remove_memory() - the check itself is > in offline_pages()) only checks if both start and end of the > to-be-removed block are aligned to pageblock_nr_pages. As you noted the > actual size and alignment requirements in __offline_isolated_pages can > be larger that that, so I think the checks in offline_pages() should be > changed (if 1<<MAX_ORDER is always >= pageblock_nr_pages) or extended > (if there can be any relation between the two). > Ok, maybe my mistake. This is a fix. Thank you for reporting. == offline_pages()'s sanity check of given range is wrong. It should be aligned to MAX_ORDER. Current exsiting caller uses SECTION_SIZE alignment, so this change has no influence to exsisting callers. Reported-by: Ingo Korb <ingo@xxxxxxxx> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> --- mm/memory_hotplug.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) Index: linux-2.6.37-rc5/mm/memory_hotplug.c =================================================================== --- linux-2.6.37-rc5.orig/mm/memory_hotplug.c +++ linux-2.6.37-rc5/mm/memory_hotplug.c @@ -798,10 +798,14 @@ static int offline_pages(unsigned long s struct memory_notify arg; BUG_ON(start_pfn >= end_pfn); - /* at least, alignment against pageblock is necessary */ - if (!IS_ALIGNED(start_pfn, pageblock_nr_pages)) + /* + * Considering buddy allocator which joins nearby pages, the range + * in offline should be aligned to MAX_ORDER. If not, isolated + * page will be joined to other (not isolated) pages. + */ + if (!IS_ALIGNED(start_pfn, MAX_ORDER_NR_PAGES)) return -EINVAL; - if (!IS_ALIGNED(end_pfn, pageblock_nr_pages)) + if (!IS_ALIGNED(end_pfn, MAX_ORDER_NR_PAGES)) return -EINVAL; /* This makes hotplug much easier...and readable. we assume this for now. .*/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>