On 3/4/22 02:59, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Cc: Wei Xu <weixugc@xxxxxxxxxx>
> Cc: Greg Thelen <gthelen@xxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> mm/page_alloc.c | 17 +++++++----------
> 1 file changed, 7 insertions(+), 10 deletions(-)
Just a quick reply from what AFAIK immediately see as a issue.
>
> 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));
>
> __mod_zone_freepage_state(zone, -(1 << order),
> get_pcppage_migratetype(page));
> - spin_unlock_irqrestore(&zone->lock, flags);
__mod_zone_freepage_state() outside the lock is AFAIK unsafe.
>
> __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
