linux-kernel - Re: [PATCH] mm/page_alloc: Fix memory accept before watermarks gets initialized

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Message-ID: <03b53f18-8c16-4716-8ed4-1902d7247354@suse.cz>
Date: Mon, 10 Mar 2025 12:37:25 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Mike Rapoport <rppt@...nel.org>, David Hildenbrand <david@...hat.com>,
 Mel Gorman <mgorman@...hsingularity.net>,
 Tom Lendacky <thomas.lendacky@....com>, "Kalra, Ashish"
 <ashish.kalra@....com>, Rick Edgecombe <rick.p.edgecombe@...el.com>,
 linux-mm@...ck.org, linux-coco@...ts.linux.dev,
 linux-kernel@...r.kernel.org, Farrah Chen <farrah.chen@...el.com>
Subject: Re: [PATCH] mm/page_alloc: Fix memory accept before watermarks gets
 initialized

On 3/10/25 09:28, Kirill A. Shutemov wrote:
> Watermarks are initialized during the postcore initcall. Until then, all
> watermarks are set to zero. This causes cond_accept_memory() to
> incorrectly skip memory acceptance because a watermark of 0 is always
> met.

What are the user-visible consequences of that?

> To ensure progress, accept one MAX_ORDER page if the watermark is zero.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reported-and-tested-by: Farrah Chen <farrah.chen@...el.com>

Fixes:, Cc: stable etc?

> ---
>  mm/page_alloc.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 579789600a3c..4fe93029bcb6 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7004,7 +7004,7 @@ static inline bool has_unaccepted_memory(void)
>  
>  static bool cond_accept_memory(struct zone *zone, unsigned int order)
>  {
> -	long to_accept;
> +	long to_accept, wmark;
>  	bool ret = false;
>  
>  	if (!has_unaccepted_memory())
> @@ -7013,8 +7013,18 @@ static bool cond_accept_memory(struct zone *zone, unsigned int order)
>  	if (list_empty(&zone->unaccepted_pages))
>  		return false;
>  
> +	wmark = promo_wmark_pages(zone);
> +
> +	/*
> +	 * Watermarks have not been initialized yet.
> +	 *
> +	 * Accepting one MAX_ORDER page to ensure progress.
> +	 */
> +	if (!wmark)
> +		return try_to_accept_memory_one(zone);
> +
>  	/* How much to accept to get to promo watermark? */
> -	to_accept = promo_wmark_pages(zone) -
> +	to_accept = wmark -
>  		    (zone_page_state(zone, NR_FREE_PAGES) -
>  		    __zone_watermark_unusable_free(zone, order, 0) -
>  		    zone_page_state(zone, NR_UNACCEPTED));