linux-kernel - Re: [PATCH v4 2/3] gup: introduce unpin_user_folio_dirty

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Message-ID: <ccabb051-e645-4a6c-8357-64a2640289c1@redhat.com>
Date: Tue, 17 Jun 2025 16:04:26 +0200
From: David Hildenbrand <david@...hat.com>
To: Jason Gunthorpe <jgg@...pe.ca>, lizhe.67@...edance.com
Cc: alex.williamson@...hat.com, akpm@...ux-foundation.org, peterx@...hat.com,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 2/3] gup: introduce unpin_user_folio_dirty_locked()

On 17.06.25 15:58, David Hildenbrand wrote:
> On 17.06.25 15:45, David Hildenbrand wrote:
>> On 17.06.25 15:42, Jason Gunthorpe wrote:
>>> On Tue, Jun 17, 2025 at 12:18:20PM +0800, lizhe.67@...edance.com wrote:
>>>
>>>> @@ -360,12 +360,7 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
>>>>     
>>>>     	for (i = 0; i < npages; i += nr) {
>>>>     		folio = gup_folio_range_next(page, npages, i, &nr);
>>>> -		if (make_dirty && !folio_test_dirty(folio)) {
>>>> -			folio_lock(folio);
>>>> -			folio_mark_dirty(folio);
>>>> -			folio_unlock(folio);
>>>> -		}
>>>> -		gup_put_folio(folio, nr, FOLL_PIN);
>>>> +		unpin_user_folio_dirty_locked(folio, nr, make_dirty);
>>>>     	}
>>>
>>> I don't think we should call an exported function here - this is a
>>> fast path for rdma and iommfd, I don't want to see it degrade to save
>>> three duplicated lines :\
>>
>> Any way to quantify? In theory, the compiler could still optimize this
>> within the same file, no?
> 
> Looking at the compiler output, I think the compile is doing exactly that.
> 
> Unless my obdjump -D -S analysis skills are seriously degraded :)

FWIW, while already looking at this, even before this change, the 
compiler does not inline gup_put_folio() into this function, which is a 
bit unexpected.

-- 
Cheers,

David / dhildenb