linux-kernel - Re: [PATCH 4/8] mm/vmalloc: Remove cond_resched() in vm_area_alloc

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Message-ID: <aKKMeUdnr/0WuQh6@MiWiFi-R3L-srv>
Date: Mon, 18 Aug 2025 10:14:17 +0800
From: Baoquan He <bhe@...hat.com>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/8] mm/vmalloc: Remove cond_resched() in
 vm_area_alloc_pages()

On 08/07/25 at 09:58am, Uladzislau Rezki (Sony) wrote:
> The vm_area_alloc_pages() function uses cond_resched() to yield the
> CPU during potentially long-running loops. However, these loops are
> not considered long-running under normal conditions. In non-blocking
> contexts, calling cond_resched() is inappropriate also.
> 
> Remove these calls to ensure correctness for blocking/non-blocking
> contexts. This also simplifies the code path. In fact, a slow path
> of page allocator already includes reschedule points to mitigate
> latency.
> 
> This patch was tested for !CONFIG_PREEMPT kernel and with large
> allocation chunks(~1GB), without triggering any "BUG: soft lockup"
> warnings.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> ---
>  mm/vmalloc.c | 2 --
>  1 file changed, 2 deletions(-)

Reviewed-by: Baoquan He <bhe@...hat.com>

> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 81b6d3bde719..b0255e0c74b3 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3633,7 +3633,6 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  							pages + nr_allocated);
>  
>  			nr_allocated += nr;
> -			cond_resched();
>  
>  			/*
>  			 * If zero or pages were obtained partly,
> @@ -3675,7 +3674,6 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  		for (i = 0; i < (1U << order); i++)
>  			pages[nr_allocated + i] = page + i;
>  
> -		cond_resched();
>  		nr_allocated += 1U << order;
>  	}
>  
> -- 
> 2.39.5
>