linux-kernel - Re: [PATCH 1/5] mm/page_alloc: Fetch the correct pcp buddy during bulk free

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Date:   Wed, 16 Feb 2022 12:16:48 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Aaron Lu <aaron.lu@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 1/5] mm/page_alloc: Fetch the correct pcp buddy during
 bulk free

On 2/15/22 15:51, Mel Gorman wrote:
> free_pcppages_bulk() prefetches buddies about to be freed but the
> order must also be passed in as PCP lists store multiple orders.
> 
> Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/page_alloc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3589febc6d31..08de32cfd9bb 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1432,10 +1432,10 @@ static bool bulkfree_pcp_prepare(struct page *page)
>  }
>  #endif /* CONFIG_DEBUG_VM */
>  
> -static inline void prefetch_buddy(struct page *page)
> +static inline void prefetch_buddy(struct page *page, unsigned int order)
>  {
>  	unsigned long pfn = page_to_pfn(page);
> -	unsigned long buddy_pfn = __find_buddy_pfn(pfn, 0);
> +	unsigned long buddy_pfn = __find_buddy_pfn(pfn, order);
>  	struct page *buddy = page + (buddy_pfn - pfn);
>  
>  	prefetch(buddy);
> @@ -1512,7 +1512,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  			 * prefetch buddy for the first pcp->batch nr of pages.
>  			 */
>  			if (prefetch_nr) {
> -				prefetch_buddy(page);
> +				prefetch_buddy(page, order);
>  				prefetch_nr--;
>  			}
>  		} while (count > 0 && --batch_free && !list_empty(list));