linux-kernel - Re: [PATCH] mm/cma: print total and used pages in cma

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Message-ID: <ee29262a-911b-4a97-b619-0dea3b657252@redhat.com>
Date: Sat, 16 Aug 2025 08:27:39 +0200
From: David Hildenbrand <david@...hat.com>
To: Xiang Gao <gxxa03070307@...il.com>, akpm@...ux-foundation.org
Cc: lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, vbabka@...e.cz,
 rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, gaoxiang17 <gaoxiang17@...omi.com>
Subject: Re: [PATCH] mm/cma: print total and used pages in cma_alloc()

On 16.08.25 06:28, Xiang Gao wrote:
> From: gaoxiang17 <gaoxiang17@...omi.com>
> 
> This makes cma info more intuitive during debugging.
> 
> before:
> [   24.407814] cma: cma_alloc(cma (____ptrval____), name: reserved, count 1, align 0)
> [   24.413397] cma: cma_alloc(cma (____ptrval____), name: reserved, count 1, align 0)
> [   24.415886] cma: cma_alloc(cma (____ptrval____), name: reserved, count 1, align 0)
> 
> after:
> [   24.069738] cma: cma_alloc(cma (____ptrval____), name: reserved, total pages: 16384, used pages: 64, request pages: 1, align 0)
> [   24.075317] cma: cma_alloc(cma (____ptrval____), name: reserved, total pages: 16384, used pages: 65, request pages: 1, align 0)
> [   24.078455] cma: cma_alloc(cma (____ptrval____), name: reserved, total pages: 16384, used pages: 66, request pages: 1, align 0)
> 
> Signed-off-by: gaoxiang17 <gaoxiang17@...omi.com>
> ---
>   mm/cma.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/cma.c b/mm/cma.c
> index 2ffa4befb99a..46cc98e7f587 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -776,6 +776,17 @@ static void cma_debug_show_areas(struct cma *cma)
>   	spin_unlock_irq(&cma->lock);
>   }
>   
> +static unsigned long cma_get_used_pages(struct cma *cma)
> +{
> +	unsigned long used;
> +
> +	spin_lock_irq(&cma->lock);
> +	used = bitmap_weight(cma->bitmap, (int)cma_bitmap_maxno(cma));
> +	spin_unlock_irq(&cma->lock);
> +
> +	return used << cma->order_per_bit;
> +}
> +
>   static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr,
>   				unsigned long count, unsigned int align,
>   				struct page **pagep, gfp_t gfp)
> @@ -858,8 +869,8 @@ static struct page *__cma_alloc(struct cma *cma, unsigned long count,
>   	if (!cma || !cma->count)
>   		return page;
>   
> -	pr_debug("%s(cma %p, name: %s, count %lu, align %d)\n", __func__,
> -		(void *)cma, cma->name, count, align);
> +	pr_debug("%s(cma %p, name: %s, total pages: %lu, used pages: %lu, request pages: %lu, align %d)\n",
> +		__func__, (void *)cma, cma->name, cma->count, cma_get_used_pages(cma), count, align);

		^ one space missing for proper indentation.

But doing another spinlock cycle just for debugging purposes? That does 
not feel right, sorry.

-- 
Cheers

David / dhildenb