linux-kernel - Re: [PATCH v3] mm/min_free_kbytes: modify min_free

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Date:   Wed, 21 Jun 2023 18:00:25 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     liuq <liuq131@...natelecom.cn>, <akpm@...ux-foundation.org>
CC:     <ying.huang@...el.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        mawupeng 00564683 <mawupeng1@...wei.com>,
        Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH v3] mm/min_free_kbytes: modify min_free_kbytes calculation
 rules

Hi Liuq,

On 2023/6/21 17:20, liuq wrote:
> The current calculation of min_free_kbytes only uses ZONE_DMA and
> ZONE_NORMAL pages,but the ZONE_MOVABLE zone->_watermark[WMARK_MIN]
> will also divide part of min_free_kbytes.This will cause the min
> watermark of ZONE_NORMAL to be too small in the presence of ZONE_MOVEABLE.
> 
> __GFP_HIGH and PF_MEMALLOC allocations usually don't need movable
> zone pages, so just like ZONE_HIGHMEM, cap pages_min to a small
> value in __setup_per_zone_wmarks.
> 
> On my testing machine with 16GB of memory (transparent hugepage is
> turned off by default, and movablecore=12G is configured)
> The following is a comparative test data of watermark_min
> 
> 		no patch	add patch
> ZONE_DMA	1		8
> ZONE_DMA32	151		709
> ZONE_NORMAL	233		1113
> ZONE_MOVABLE	1434		128
> min_free_kbytes	7288		7326
> 

We see this issue and do the same change[1], and we add a per zone 
watermark configuration too, but both of them is not accepted,
let's add Mel and wupeng to see more comments.

[1]https://lore.kernel.org/linux-mm/20220905032858.1462927-1-mawupeng1@huawei.com/

> Signed-off-by: liuq <liuq131@...natelecom.cn>
> ---
>   mm/page_alloc.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 47421bedc12b..590ed8725e09 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6362,9 +6362,9 @@ static void __setup_per_zone_wmarks(void)
>   	struct zone *zone;
>   	unsigned long flags;
>   
> -	/* Calculate total number of !ZONE_HIGHMEM pages */
> +	/* Calculate total number of !ZONE_HIGHMEM and !ZONE_MOVABLE pages */
>   	for_each_zone(zone) {
> -		if (!is_highmem(zone))
> +		if (!is_highmem(zone) && zone_idx(zone) != ZONE_MOVABLE)
>   			lowmem_pages += zone_managed_pages(zone);
>   	}
>   
> @@ -6374,15 +6374,15 @@ 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
> -			 * value here.
> +			 * need highmem and movable zones pages, so cap pages_min
> +			 * to a small  value here.
>   			 *
>   			 * The WMARK_HIGH-WMARK_LOW and (WMARK_LOW-WMARK_MIN)
>   			 * deltas control async page reclaim, and so should
> -			 * not be capped for highmem.
> +			 * not be capped for highmem and movable zones.
>   			 */
>   			unsigned long min_pages;
>