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

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Message-Id: <20260129141057.b577100c834c726f01a602b9@linux-foundation.org>
Date: Thu, 29 Jan 2026 14:10:57 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: "shengminghu512" <shengminghu512@...com>
Cc: "vbabka" <vbabka@...e.cz>, "surenb" <surenb@...gle.com>, "mhocko"
 <mhocko@...e.com>, "jackmanb" <jackmanb@...gle.com>, "hannes"
 <hannes@...xchg.org>, "ziy" <ziy@...dia.com>, "inux-mm"
 <inux-mm@...ck.org>, "linux-kernel" <linux-kernel@...r.kernel.org>,
 "hu.shengming" <hu.shengming@....com.cn>, "zhang.run"
 <zhang.run@....com.cn>
Subject: Re: [PATCH linux-next] mm/page_alloc: avoid overcounting bulk alloc
 in watermark check

On Thu, 29 Jan 2026 22:38:14 +0800 "shengminghu512" <shengminghu512@...com> wrote:

> From: Shengming Hu <hu.shengming@....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.

Thanks.

> --- 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)) {

So that little optimization hasn't been working for four years?