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. Good question, I tried to be careful of what I touch. Thoughts? -- Thanks, David / dhildenb
