Re: [PATCH linux-next] mm/page_alloc: avoid overcounting bulk alloc in watermark check

[Vlastimil Babka <vbabka@suse.cz>]

On 1/29/26 15:38, shengminghu512 wrote:
> From: Shengming Hu <hu.shengming@zte.com.cn>
> 
> alloc_pages_bulk_noprof() only fills NULL slots and already tracks how many
> entries are pre-populated via nr_populated.
> 
> The fast watermark check was adding nr_pages unconditionally, which can
> overestimate the demand. Use (nr_pages - nr_populated) instead, as an 
> upper bound on the remaining pages this call can still allocate without
> scanning the whole array.
> 
> Signed-off-by: Shengming Hu <hu.shengming@zte.com.cn>

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

> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5fd9e4a03..90b978802 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5130,7 +5130,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
>  
>  		cond_accept_memory(zone, 0, alloc_flags);
>  retry_this_zone:
> -		mark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK) + nr_pages;
> +		mark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK) + nr_pages - nr_populated;
>  		if (zone_watermark_fast(zone, 0,  mark,
>  				zonelist_zone_idx(ac.preferred_zoneref),
>  				alloc_flags, gfp)) {