On Thu, Oct 19, 2017 at 09:15:03AM +0200, Michal Hocko wrote: > On Thu 19-10-17 11:51:11, Joonsoo Kim wrote: > > On Fri, Oct 13, 2017 at 02:00:12PM +0200, Michal Hocko wrote: > > > From: Michal Hocko <mhocko@xxxxxxxx> > > > > > > Michael has noticed that the memory offline tries to migrate kernel code > > > pages when doing > > > echo 0 > /sys/devices/system/memory/memory0/online > > > > > > The current implementation will fail the operation after several failed > > > page migration attempts but we shouldn't even attempt to migrate > > > that memory and fail right away because this memory is clearly not > > > migrateable. This will become a real problem when we drop the retry loop > > > counter resp. timeout. > > > > > > The real problem is in has_unmovable_pages in fact. We should fail if > > > there are any non migrateable pages in the area. In orther to guarantee > > > that remove the migrate type checks because MIGRATE_MOVABLE is not > > > guaranteed to contain only migrateable pages. It is merely a heuristic. > > > Similarly MIGRATE_CMA does guarantee that the page allocator doesn't > > > allocate any non-migrateable pages from the block but CMA allocations > > > themselves are unlikely to migrateable. Therefore remove both checks. > > > > Hello, > > > > This patch will break the CMA user. As you mentioned, CMA allocation > > itself isn't migrateable. So, after a single page is allocated through > > CMA allocation, has_unmovable_pages() will return true for this > > pageblock. Then, futher CMA allocation request to this pageblock will > > fail because it requires isolating the pageblock. > > Hmm, does this mean that the CMA allocation path depends on > has_unmovable_pages to return false here even though the memory is not > movable? This sounds really strange to me and kind of abuse of this Your understanding is correct. Perhaps, abuse or wrong function name. > function. Which path is that? Can we do the migrate type test theres? alloc_contig_range() -> start_isolate_page_range() -> set_migratetype_isolate() -> has_unmovable_pages() We can add one argument, 'XXX' to set_migratetype_isolate() and change it to check migrate type rather than has_unmovable_pages() if 'XXX' is specified. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
