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

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Message-ID: <701bfbb4-6c12-4614-a322-def3ca923c78@redhat.com>
Date: Sat, 16 Aug 2025 08:56:47 +0200
From: David Hildenbrand <david@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Xiang Gao <gxxa03070307@...il.com>, 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 08:45, Andrew Morton wrote:
> On Sat, 16 Aug 2025 08:27:39 +0200 David Hildenbrand <david@...hat.com> wrote:
> 
>>> @@ -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.
> 
> If we're calling pr_debug() frequently enough for this to matter, we
> have other problems!

We call it for each and every actual CMA allocation? I really don't see 
why we want to just randomly make CMA allocation latency worse.

Is the existing pr_debug() a problem? Maybe. But who actually has debug 
messages enabled in any sane setup?

-- 
Cheers

David / dhildenb