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

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

[Vlastimil Babka]

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@linux.intel.com>
> Reported-and-tested-by: Farrah Chen <farrah.chen@intel.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));

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

[Kirill A. Shutemov]

On Mon, Mar 10, 2025 at 12:37:25PM +0100, Vlastimil Babka wrote:
> 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?

Premature OOM on boot.

It can be triggered with certain combinations of number of vCPUs and
memory size.

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

Fixes: dcdfdd40fa82 ("mm: Add support for unaccepted memory")
Cc: stable@@vger.kernel.org # v6.5+

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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

[Vlastimil Babka]

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

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  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));

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

[Gupta, Pankaj]

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

Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>

Also, did a basic boot test of SNP guest kernel 6.14-rc6 with the patch 
applied on top.

> ---
>   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));