Re: [PATCH v1 4/5] mm/page_alloc: place pages to tail in __free_pages_core()

[Pankaj Gupta]

> __free_pages_core() is used when exposing fresh memory to the buddy
> during system boot and when onlining memory in generic_online_page().
>
> generic_online_page() is used in two cases:
>
> 1. Direct memory onlining in online_pages().
> 2. Deferred memory onlining in memory-ballooning-like mechanisms (HyperV
>    balloon and virtio-mem), when parts of a section are kept
>    fake-offline to be fake-onlined later on.
>
> In 1, we already place pages to the tail of the freelist. Pages will be
> freed to MIGRATE_ISOLATE lists first and moved to the tail of the freelists
> via undo_isolate_page_range().
>
> In 2, we currently don't implement a proper rule. In case of virtio-mem,
> where we currently always online MAX_ORDER - 1 pages, the pages will be
> placed to the HEAD of the freelist - undesireable. While the hyper-v
> balloon calls generic_online_page() with single pages, usually it will
> call it on successive single pages in a larger block.
>
> The pages are fresh, so place them to the tail of the freelists and avoid
> the PCP. In __free_pages_core(), remove the now superflouos call to
> set_page_refcounted() and add a comment regarding page initialization and
> the refcount.
>
> Note: In 2. we currently don't shuffle. If ever relevant (page shuffling
> is usually of limited use in virtualized environments), we might want to
> shuffle after a sequence of generic_online_page() calls in the
> relevant callers.
>
> Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
> 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: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
> Cc: Wei Liu <wei.liu@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
>  mm/page_alloc.c | 37 ++++++++++++++++++++++++-------------
>  1 file changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d5a5f528b8ca..8a2134fe9947 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -270,7 +270,8 @@ bool pm_suspended_storage(void)
>  unsigned int pageblock_order __read_mostly;
>  #endif
>
> -static void __free_pages_ok(struct page *page, unsigned int order);
> +static void __free_pages_ok(struct page *page, unsigned int order,
> +                           fop_t fop_flags);
>
>  /*
>   * results with 256, 32 in the lowmem_reserve sysctl:
> @@ -682,7 +683,7 @@ static void bad_page(struct page *page, const char *reason)
>  void free_compound_page(struct page *page)
>  {
>         mem_cgroup_uncharge(page);
> -       __free_pages_ok(page, compound_order(page));
> +       __free_pages_ok(page, compound_order(page), FOP_NONE);
>  }
>
>  void prep_compound_page(struct page *page, unsigned int order)
> @@ -1419,17 +1420,15 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>         spin_unlock(&zone->lock);
>  }
>
> -static void free_one_page(struct zone *zone,
> -                               struct page *page, unsigned long pfn,
> -                               unsigned int order,
> -                               int migratetype)
> +static void free_one_page(struct zone *zone, struct page *page, unsigned long pfn,
> +                         unsigned int order, int migratetype, fop_t fop_flags)
>  {
>         spin_lock(&zone->lock);
>         if (unlikely(has_isolate_pageblock(zone) ||
>                 is_migrate_isolate(migratetype))) {
>                 migratetype = get_pfnblock_migratetype(page, pfn);
>         }
> -       __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
> +       __free_one_page(page, pfn, zone, order, migratetype, fop_flags);
>         spin_unlock(&zone->lock);
>  }
>
> @@ -1507,7 +1506,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
>         }
>  }
>
> -static void __free_pages_ok(struct page *page, unsigned int order)
> +static void __free_pages_ok(struct page *page, unsigned int order,
> +                           fop_t fop_flags)
>  {
>         unsigned long flags;
>         int migratetype;
> @@ -1519,7 +1519,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
>         migratetype = get_pfnblock_migratetype(page, pfn);
>         local_irq_save(flags);
>         __count_vm_events(PGFREE, 1 << order);
> -       free_one_page(page_zone(page), page, pfn, order, migratetype);
> +       free_one_page(page_zone(page), page, pfn, order, migratetype,
> +                     fop_flags);
>         local_irq_restore(flags);
>  }
>
> @@ -1529,6 +1530,11 @@ void __free_pages_core(struct page *page, unsigned int order)
>         struct page *p = page;
>         unsigned int loop;
>
> +       /*
> +        * When initializing the memmap, init_single_page() sets the refcount
> +        * of all pages to 1 ("allocated"/"not free"). We have to set the
> +        * refcount of all involved pages to 0.
> +        */
>         prefetchw(p);
>         for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
>                 prefetchw(p + 1);
> @@ -1539,8 +1545,12 @@ void __free_pages_core(struct page *page, unsigned int order)
>         set_page_count(p, 0);
>
>         atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
> -       set_page_refcounted(page);
> -       __free_pages(page, order);
> +
> +       /*
> +        * Bypass PCP and place fresh pages right to the tail, primarily
> +        * relevant for memory onlining.
> +        */
> +       __free_pages_ok(page, order, FOP_TO_TAIL);
>  }
>
>  #ifdef CONFIG_NEED_MULTIPLE_NODES
> @@ -3171,7 +3181,8 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn)
>          */
>         if (migratetype >= MIGRATE_PCPTYPES) {
>                 if (unlikely(is_migrate_isolate(migratetype))) {
> -                       free_one_page(zone, page, pfn, 0, migratetype);
> +                       free_one_page(zone, page, pfn, 0, migratetype,
> +                                     FOP_NONE);
>                         return;
>                 }
>                 migratetype = MIGRATE_MOVABLE;
> @@ -5063,7 +5074,7 @@ static inline void free_the_page(struct page *page, unsigned int order)
>         if (order == 0)         /* Via pcp? */
>                 free_unref_page(page);
>         else
> -               __free_pages_ok(page, order);
> +               __free_pages_ok(page, order, FOP_NONE);
>  }
>
>  void __free_pages(struct page *page, unsigned int order)

Acked-by: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>