From: David Hildenbrand <david@xxxxxxxxxx> Subject: mm/page_alloc: tweak comments in has_unmovable_pages() Patch series "mm / virtio-mem: support ZONE_MOVABLE", v5. When introducing virtio-mem, the semantics of ZONE_MOVABLE were rather unclear, which is why we special-cased ZONE_MOVABLE such that partially plugged blocks would never end up in ZONE_MOVABLE. Now that the semantics are much clearer (and are documented in patch #6), let's support partially plugged memory blocks in ZONE_MOVABLE, allowing partially plugged memory blocks to be online to ZONE_MOVABLE and also unplugging from such memory blocks. This avoids surprises when onlining of memory blocks suddenly fails, just because they are not completely populated by virtio-mem (yet). This is especially helpful for testing, but also paves the way for virtio-mem optimizations, allowing more memory to get reliably unplugged. Cleanup has_unmovable_pages() and set_migratetype_isolate(), providing better documentation of how ZONE_MOVABLE interacts with different kind of unmovable pages (memory offlining vs. alloc_contig_range()). This patch (of 6): Let's move the split comment regarding bootmem allocations and memory holes, especially in the context of ZONE_MOVABLE, to the PageReserved() check. Link: http://lkml.kernel.org/r/20200816125333.7434-1-david@xxxxxxxxxx Link: http://lkml.kernel.org/r/20200816125333.7434-2-david@xxxxxxxxxx Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Baoquan He <bhe@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx> Cc: Jason Wang <jasowang@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxx> Cc: Qian Cai <cai@xxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_alloc.c | 22 ++++++---------------- 1 file changed, 6 insertions(+), 16 deletions(-) --- a/mm/page_alloc.c~mm-page_alloc-tweak-comments-in-has_unmovable_pages +++ a/mm/page_alloc.c @@ -8235,14 +8235,6 @@ struct page *has_unmovable_pages(struct unsigned long iter = 0; unsigned long pfn = page_to_pfn(page); - /* - * TODO we could make this much more efficient by not checking every - * page in the range if we know all of them are in MOVABLE_ZONE and - * that the movable zone guarantees that pages are migratable but - * the later is not the case right now unfortunatelly. E.g. movablecore - * can still lead to having bootmem allocations in zone_movable. - */ - if (is_migrate_cma_page(page)) { /* * CMA allocations (alloc_contig_range) really need to mark @@ -8261,6 +8253,12 @@ struct page *has_unmovable_pages(struct page = pfn_to_page(pfn + iter); + /* + * Both, bootmem allocations and memory holes are marked + * PG_reserved and are unmovable. We can even have unmovable + * allocations inside ZONE_MOVABLE, for example when + * specifying "movablecore". + */ if (PageReserved(page)) return page; @@ -8334,14 +8332,6 @@ struct page *has_unmovable_pages(struct * it. But now, memory offline itself doesn't call * shrink_node_slabs() and it still to be fixed. */ - /* - * If the page is not RAM, page_count()should be 0. - * we don't need more check. This is an _used_ not-movable page. - * - * The problematic thing here is PG_reserved pages. PG_reserved - * is set to both of a memory hole page and a _used_ kernel - * page at boot. - */ return page; } return NULL; _
