On Mon, Sep 28, 2020 at 08:21:07PM +0200, David Hildenbrand wrote: >__putback_isolated_page() already documents that pages will be placed to >the tail of the freelist - this is, however, not the case for >"order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be >the case for all existing users. > >This change affects two users: >- free page reporting >- page isolation, when undoing the isolation (including memory onlining). > >This behavior is desireable for pages that haven't really been touched >lately, so exactly the two users that don't actually read/write page >content, but rather move untouched pages. > >The new behavior is especially desirable for memory onlining, where we >allow allocation of newly onlined pages via undo_isolate_page_range() >in online_pages(). Right now, we always place them to the head of the >free list, resulting in undesireable behavior: Assume we add >individual memory chunks via add_memory() and online them right away to >the NORMAL zone. We create a dependency chain of unmovable allocations >e.g., via the memmap. The memmap of the next chunk will be placed onto >previous chunks - if the last block cannot get offlined+removed, all >dependent ones cannot get offlined+removed. While this can already be >observed with individual DIMMs, it's more of an issue for virtio-mem >(and I suspect also ppc DLPAR). > >Document that this should only be used for optimizations, and no code >should realy on this for correction (if the order of freepage lists >ever changes). > >We won't care about page shuffling: memory onlining already properly >shuffles after onlining. free page reporting doesn't care about >physically contiguous ranges, and there are already cases where page >isolation will simply move (physically close) free pages to (currently) >the head of the freelists via move_freepages_block() instead of >shuffling. If this becomes ever relevant, we should shuffle the whole >zone when undoing isolation of larger ranges, and after >free_contig_range(). > >Reviewed-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> >Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> >Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> >Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> >Cc: Michal Hocko <mhocko@xxxxxxxxxx> >Cc: Dave Hansen <dave.hansen@xxxxxxxxx> >Cc: Vlastimil Babka <vbabka@xxxxxxx> >Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> >Cc: Oscar Salvador <osalvador@xxxxxxx> >Cc: Mike Rapoport <rppt@xxxxxxxxxx> >Cc: Scott Cheloha <cheloha@xxxxxxxxxxxxx> >Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> >Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> >--- > mm/page_alloc.c | 18 ++++++++++++++++-- > 1 file changed, 16 insertions(+), 2 deletions(-) > >diff --git a/mm/page_alloc.c b/mm/page_alloc.c >index daab90e960fe..9e3ed4a6f69a 100644 >--- a/mm/page_alloc.c >+++ b/mm/page_alloc.c >@@ -89,6 +89,18 @@ typedef int __bitwise fop_t; > */ > #define FOP_SKIP_REPORT_NOTIFY ((__force fop_t)BIT(0)) > >+/* >+ * Place the (possibly merged) page to the tail of the freelist. Will ignore >+ * page shuffling (relevant code - e.g., memory onlining - is expected to >+ * shuffle the whole zone). >+ * >+ * Note: No code should rely onto this flag for correctness - it's purely >+ * to allow for optimizations when handing back either fresh pages >+ * (memory onlining) or untouched pages (page isolation, free page >+ * reporting). >+ */ >+#define FOP_TO_TAIL ((__force fop_t)BIT(1)) >+ > /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */ > static DEFINE_MUTEX(pcp_batch_high_lock); > #define MIN_PERCPU_PAGELIST_FRACTION (8) >@@ -1038,7 +1050,9 @@ static inline void __free_one_page(struct page *page, unsigned long pfn, > done_merging: > set_page_order(page, order); > >- if (is_shuffle_order(order)) >+ if (fop_flags & FOP_TO_TAIL) >+ to_tail = true; >+ else if (is_shuffle_order(order)) > to_tail = shuffle_pick_tail(); > else > to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order); >@@ -3300,7 +3314,7 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt) > > /* Return isolated page to tail of freelist. */ > __free_one_page(page, page_to_pfn(page), zone, order, mt, >- FOP_SKIP_REPORT_NOTIFY); >+ FOP_SKIP_REPORT_NOTIFY | FOP_TO_TAIL); > } > > /* >-- >2.26.2 -- Wei Yang Help you, Help me
