linux-kernel - Re: [PATCH v2 1/5] mm,hugetlb: Change mechanism to detect a COW on private mapping

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Message-ID: <ab9efb5b-66ce-46f3-b0be-544f202d9190@redhat.com>
Date: Wed, 25 Jun 2025 12:13:12 +0200
From: David Hildenbrand <david@...hat.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Muchun Song <muchun.song@...ux.dev>, Peter Xu <peterx@...hat.com>,
 Gavin Guo <gavinguo@...lia.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] mm,hugetlb: Change mechanism to detect a COW on
 private mapping

On 25.06.25 09:49, Oscar Salvador wrote:
> On Mon, Jun 23, 2025 at 04:09:51PM +0200, David Hildenbrand wrote:
>>
>>> -	/*
>>> -	 * hugetlb_wp() requires page locks of pte_page(vmf.orig_pte) and
>>> -	 * pagecache_folio, so here we need take the former one
>>> -	 * when folio != pagecache_folio or !pagecache_folio.
>>> -	 */
>>> +	/* hugetlb_wp() requires page locks of pte_page(vmf.orig_pte) */
>>>    	folio = page_folio(pte_page(vmf.orig_pte));
>>> -	if (folio != pagecache_folio)
>>> -		if (!folio_trylock(folio)) {
>>> -			need_wait_lock = 1;
>>> -			goto out_ptl;
>>> -		}
>>> -
>>> +	folio_lock(folio);
>>>    	folio_get(folio);
>>
>> Just realized that this won't work for this patch here, as we are holding
>> the PTL.
>>
>> In patch #2 you do the right thing.
> 
> Yap, missed that.
> I might have to do the lock-unlock-dance here, and then in patch#2 move
> it to hugetlb_wp.
> Sounds reasonable?

Yes

-- 
Cheers,

David / dhildenb