linux-kernel - Re: [PATCH v4] mm/page_alloc: fix min_free_kbytes calculation regarding ZONE

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Message-ID: <87leg86zkx.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Sun, 25 Jun 2023 10:33:02 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     liuq <liuq131@...natelecom.cn>
Cc:     <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] mm/page_alloc: fix min_free_kbytes calculation
 regarding ZONE_MOVABLE

liuq <liuq131@...natelecom.cn> writes:

> 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.
           ~~~~~~~~~~~~~~~~~~~~~~~

Better to add () in function name to make it easier to understand.  That
is, "__setup_per_zone_wmarks()".

Otherwise looks good to me.

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

>
> 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
>
> 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;
>   
> -- 2.27.0