On Fri, Oct 13, 2017 at 02:00:12PM +0200, Michal Hocko wrote: > From: Michal Hocko <mho...@suse.com> > > 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. Thanks.
