Hi, On Mon 23-08-10 11:22:46, Michal Hocko wrote: > On Sun 22-08-10 08:42:32, Wu Fengguang wrote: > > Hi Michal, > > Hi, > > > > > It helps to explain in changelog/code > > > > - in what situation a ZONE_MOVABLE will contain !MIGRATE_MOVABLE > > pages? > > page can be MIGRATE_RESERVE IIUC. > > > And why the MIGRATE_MOVABLE test is still necessary given the > > ZONE_MOVABLE check? > > I would assume that the MIGRATE_MOVABLE test is not necessary (given that > the whole zone is set as movable) but this test is used also in the > offlining path (in set_migratetype_isolate) and the primary reason for > this patch is to sync those two checks. > > I am not familiar with all the possible cases for migrate flags so the > test reduction should be better done by someone more familiar with the > code (the zone flag test is much more easier than the whole > get_pageblock_migratetype so this could be a win in the end). > > > > > - why do you think free pages are not removeable? Simply to cater for > > the set_migratetype_isolate() logic, or there are more fundamental > > reasons? > > Free pages can be from non movable zone, right? I know that having a > zone with the free page blocks in non-movable zone is extremely > improbable but what is the point of this check anyway? So yes, this is > more to be in sync than anything more fundamental. Are there any other comments on this? Is the patch reasonable at all? > > > > > Thanks, > > Fengguang > > > > On Fri, Aug 20, 2010 at 04:14:00PM +0200, Michal Hocko wrote: > > > Hi, > > > what do you think about the patch below? > > > > > > >From b983695b92b5be58f31c719fada1d3245f7b6768 Mon Sep 17 00:00:00 2001 > > > From: Michal Hocko <mhocko@xxxxxxx> > > > Date: Fri, 20 Aug 2010 15:39:16 +0200 > > > Subject: [PATCH] Make is_mem_section_removable more conformable with offlining code > > > > > > Currently is_mem_section_removable checks whether each pageblock from > > > the given pfn range is of MIGRATE_MOVABLE type or if it is free. If both > > > are false then the range is considered non removable. > > > > > > On the other hand, offlining code (more specifically > > > set_migratetype_isolate) doesn't care whether a page is free and instead > > > it just checks the migrate type of the page and whether the page's zone > > > is movable. > > > > > > This can lead into a situation when a node is marked as removable even > > > though all pages are neither MIGRATE_MOVABLE nor the zone is > > > ZONE_MOVABLE. > > > > > > Also we can mark a node as not removable just because a pageblock is > > > MIGRATE_RESERVE and not free (and this situation is much more probable). > > > --- > > > mm/memory_hotplug.c | 6 +++--- > > > 1 files changed, 3 insertions(+), 3 deletions(-) > > > > > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > > > index a4cfcdc..da20568 100644 > > > --- a/mm/memory_hotplug.c > > > +++ b/mm/memory_hotplug.c > > > @@ -611,10 +611,10 @@ int is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages) > > > type = get_pageblock_migratetype(page); > > > > > > /* > > > - * A pageblock containing MOVABLE or free pages is considered > > > - * removable > > > + * A pageblock containing MOVABLE or page from movable > > > + * zone are considered removable > > > */ > > > - if (type != MIGRATE_MOVABLE && !pageblock_free(page)) > > > + if (type != MIGRATE_MOVABLE && zone_idx(page) != ZONE_MOVABLE) > > > return 0; > > > > > > /* -- Michal Hocko L3 team SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>