linux-kernel - Re: [PATCH 4/6] mm/page_alloc: Drain the requested list first during bulk free

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Date:   Thu, 17 Feb 2022 10:42:09 +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 4/6] mm/page_alloc: Drain the requested list first during
 bulk free

On 2/17/22 01:22, Mel Gorman wrote:
> Prior to the series, pindex 0 (order-0 MIGRATE_UNMOVABLE) was always
> skipped first and the precise reason is forgotten. A potential reason may
> have been to artificially preserve MIGRATE_UNMOVABLE but there is no reason
> why that would be optimal as it depends on the workload. The more likely
> reason is that it was less complicated to do a pre-increment instead of
> a post-increment in terms of overall code flow. As free_pcppages_bulk()
> now typically receives the pindex of the PCP list that exceeded high,
> always start draining that list.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

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

> ---
>  mm/page_alloc.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index dfc347a58ea6..635a4e0f70b4 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1463,6 +1463,10 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  	 * below while (list_empty(list)) loop.
>  	 */
>  	count = min(pcp->count, count);
> +
> +	/* Ensure requested pindex is drained first. */
> +	pindex = pindex - 1;
> +
>  	while (count > 0) {
>  		struct list_head *list;
>  		int nr_pages;