Re: [PATCH] mm/page_alloc: call check_new_pages() while zone spinlock is not held

[Eric Dumazet <edumazet@google.com>]

On Thu, Mar 3, 2022 at 5:59 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
> From: Eric Dumazet <edumazet@google.com>
>
> For high order pages not using pcp, rmqueue() is currently calling
> the costly check_new_pages() while zone spinlock is held.
>
> This is not needed, we can release the spinlock sooner to reduce
> zone spinlock contention.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: Greg Thelen <gthelen@google.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: David Rientjes <rientjes@google.com>
> ---
>  mm/page_alloc.c | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3589febc6d31928f850ebe5a4015ddc40e0469f3..0890a65f8cc2259e82bc1f5ba95a592fb30f9fb8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3685,7 +3685,6 @@ struct page *rmqueue(struct zone *preferred_zone,
>                         gfp_t gfp_flags, unsigned int alloc_flags,
>                         int migratetype)
>  {
> -       unsigned long flags;
>         struct page *page;
>
>         if (likely(pcp_allowed_order(order))) {
> @@ -3706,10 +3705,12 @@ struct page *rmqueue(struct zone *preferred_zone,
>          * allocate greater than order-1 page units with __GFP_NOFAIL.
>          */
>         WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
> -       spin_lock_irqsave(&zone->lock, flags);
>
>         do {
> +               unsigned long flags;
> +
>                 page = NULL;
> +               spin_lock_irqsave(&zone->lock, flags);
>                 /*
>                  * order-0 request can reach here when the pcplist is skipped
>                  * due to non-CMA allocation context. HIGHATOMIC area is
> @@ -3723,13 +3724,13 @@ struct page *rmqueue(struct zone *preferred_zone,
>                 }
>                 if (!page)
>                         page = __rmqueue(zone, order, migratetype, alloc_flags);
> -       } while (page && check_new_pages(page, order));
> -       if (!page)
> -               goto failed;
> +               spin_unlock_irqrestore(&zone->lock, flags);
> +               if (!page)
> +                       return NULL;
> +       } while (check_new_pages(page, order));
>

Oh well, it seems hard irqs have to be disabled when calling the
following function.

I will send a V2.

>         __mod_zone_freepage_state(zone, -(1 << order),
>                                   get_pcppage_migratetype(page));
> -       spin_unlock_irqrestore(&zone->lock, flags);
>
>         __count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
>         zone_statistics(preferred_zone, zone, 1);
> @@ -3743,10 +3744,6 @@ struct page *rmqueue(struct zone *preferred_zone,
>
>         VM_BUG_ON_PAGE(page && bad_range(zone, page), page);
>         return page;
> -
> -failed:
> -       spin_unlock_irqrestore(&zone->lock, flags);
> -       return NULL;
>  }
>
>  #ifdef CONFIG_FAIL_PAGE_ALLOC
> --
> 2.35.1.616.g0bdcbb4464-goog
>