On Mon, Oct 05, 2020 at 08:56:48AM +0200, Michal Hocko wrote: > On Fri 02-10-20 17:20:09, David Hildenbrand wrote: > > On 02.10.20 15:24, Michal Hocko wrote: > > > On Mon 28-09-20 20:21:08, David Hildenbrand wrote: > > >> Page isolation doesn't actually touch the pages, it simply isolates > > >> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist. > > >> > > >> We already place pages to the tail of the freelists when undoing > > >> isolation via __putback_isolated_page(), let's do it in any case > > >> (e.g., if order <= pageblock_order) and document the behavior. > > >> > > >> Add a "to_tail" parameter to move_freepages_block() but introduce a > > >> a new move_to_free_list_tail() - similar to add_to_free_list_tail(). > > >> > > >> This change results in all pages getting onlined via online_pages() to > > >> be placed to the tail of the freelist. > > > > > > Is there anything preventing to do this unconditionally? Or in other > > > words is any of the existing callers of move_freepages_block benefiting > > > from adding to the head? > > > > 1. mm/page_isolation.c:set_migratetype_isolate() > > > > We move stuff to the MIGRATE_ISOLATE list, we don't care about the order > > there. > > > > 2. steal_suitable_fallback(): > > > > I don't think we care too much about the order when already stealing > > pageblocks ... and the freelist is empty I guess? > > > > 3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock() > > > > Not sure if we really care. > > Honestly, I have no idea. I can imagine that some atomic high order > workloads (e.g. in net) might benefit from cache line hot pages but I am > not sure this is really observable. The highatomic reserve is more concerned that about the allocation succeeding than it is about cache hotness. -- Mel Gorman SUSE Labs
