linux-kernel - Re: [PATCH v2 1/2] mm: Cap zone movable's min wmark to small value

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Date:   Wed, 24 Aug 2022 10:10:36 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Wupeng Ma <mawupeng1@...wei.com>, akpm@...ux-foundation.org
Cc:     corbet@....net, mcgrof@...nel.org, keescook@...omium.org,
        yzaikin@...gle.com, songmuchun@...edance.com,
        mike.kravetz@...cle.com, osalvador@...e.de, rppt@...nel.org,
        surenb@...gle.com, jsavitz@...hat.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, wangkefeng.wang@...wei.com
Subject: Re: [PATCH v2 1/2] mm: Cap zone movable's min wmark to small value

On 19.08.22 11:30, Wupeng Ma wrote:
> From: Ma Wupeng <mawupeng1@...wei.com>
> 
> Since min_free_kbytes is based on gfp_zone(GFP_USER) which does not include
> zone movable. However zone movable will get its min share in
> __setup_per_zone_wmarks() which does not make any sense.
> 
> And like highmem pages, __GFP_HIGH and PF_MEMALLOC allocations usually
> don't need movable pages, so there is no need to assign min pages for zone
> movable.
> 
> Let's cap pages_min for zone movable to a small value here just link
> highmem pages.
> 
> Signed-off-by: Ma Wupeng <mawupeng1@...wei.com>
> ---
>  mm/page_alloc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e5486d47406e..ff644205370f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8638,7 +8638,7 @@ static void __setup_per_zone_wmarks(void)
>  
>  	/* Calculate total number of !ZONE_HIGHMEM pages */
>  	for_each_zone(zone) {
> -		if (!is_highmem(zone))
> +		if (!is_highmem(zone) && zone_idx(zone) != ZONE_MOVABLE)
>  			lowmem_pages += zone_managed_pages(zone);
>  	}
>  
> @@ -8648,7 +8648,7 @@ static void __setup_per_zone_wmarks(void)
>  		spin_lock_irqsave(&zone->lock, flags);
>  		tmp = (u64)pages_min * zone_managed_pages(zone);
>  		do_div(tmp, lowmem_pages);
> -		if (is_highmem(zone)) {
> +		if (is_highmem(zone) || zone_idx(zone) == ZONE_MOVABLE) {
>  			/*
>  			 * __GFP_HIGH and PF_MEMALLOC allocations usually don't
>  			 * need highmem pages, so cap pages_min to a small

This kind-off makes sense to me, but I'm not completely sure about all
implications. We most certainly should update the comment as well.

-- 
Thanks,

David / dhildenb