linux-kernel - Re: [PATCH] mm: remove lru_add_drain_all in alloc_contig

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Date:   Tue, 9 Feb 2021 19:17:59 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm: remove lru_add_drain_all in alloc_contig_range

On 09.02.21 18:50, Minchan Kim wrote:
> __alloc_contig_migrate_range already has lru_add_drain_all call
> via migrate_prep. It's necessary to move LRU taget pages into
> LRU list to be able to isolated. However, lru_add_drain_all call
> after __alloc_contig_migrate_range is called is pointless.
> 
> This patch removes it.
> 
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>   mm/page_alloc.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6446778cbc6b..f8fbee73dd6d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8603,8 +8603,6 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>   	 * isolated thus they won't get removed from buddy.
>   	 */
>   
> -	lru_add_drain_all();
> -
>   	order = 0;
>   	outer_start = start;
>   	while (!PageBuddy(pfn_to_page(outer_start))) {
> 

I was expecting some magical reason why this is still required but I am 
not able to find a compelling one. Maybe this is really some historical 
artifact.

Let's see if other people know why this call here still exists.

-- 
Thanks,

David / dhildenb