Re: [PATCH] mm/page_alloc: Fix zone reserve update serialization

[Michal Hocko <mhocko@suse.com>]

On Mon 11-05-26 20:04:09, Muchun Song wrote:
> Serialize lowmem reserve and watermark updates with the same lock so
> calculate_totalreserve_pages() cannot observe partially updated zone
> reserve state.

Could you describe the problem you are facing?

> Fixes: 9726891fe753 ("mm: page_alloc: fix missed updates of lowmem_reserve in adjust_managed_page_count")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/page_alloc.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3a56825a7fc5..0989067da588 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6384,6 +6384,8 @@ static void calculate_totalreserve_pages(void)
>  	trace_mm_calculate_totalreserve_pages(totalreserve_pages);
>  }
>  
> +static DEFINE_SPINLOCK(zone_reserve_lock);
> +
>  /*
>   * setup_per_zone_lowmem_reserve - called whenever
>   *	sysctl_lowmem_reserve_ratio changes.  Ensures that each zone
> @@ -6394,6 +6396,8 @@ static void setup_per_zone_lowmem_reserve(void)
>  {
>  	struct pglist_data *pgdat;
>  	enum zone_type i, j;
> +
> +	guard(spinlock_irqsave)(&zone_reserve_lock);
>  	/*
>  	 * For a given zone node_zones[i], lowmem_reserve[j] (j > i)
>  	 * represents how many pages in zone i must effectively be kept
> @@ -6509,11 +6513,9 @@ static void __setup_per_zone_wmarks(void)
>  void setup_per_zone_wmarks(void)
>  {
>  	struct zone *zone;
> -	static DEFINE_SPINLOCK(lock);
>  
> -	spin_lock(&lock);
> -	__setup_per_zone_wmarks();
> -	spin_unlock(&lock);
> +	scoped_guard(spinlock_irqsave, &zone_reserve_lock)
> +		__setup_per_zone_wmarks();
>  
>  	/*
>  	 * The watermark size have changed so update the pcpu batch
> 
> base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
> -- 
> 2.54.0

-- 
Michal Hocko
SUSE Labs