linux-kernel - Re: [PATCH v3 2/4] mm/huge_memory: replace can_split

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Message-ID: <992DA160-BF2B-4D38-B76C-481F49155652@nvidia.com>
Date: Wed, 26 Nov 2025 11:59:34 -0500
From: Zi Yan <ziy@...dia.com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>,
 Miaohe Lin <linmiaohe@...wei.com>, Naoya Horiguchi <nao.horiguchi@...il.com>,
 Wei Yang <richard.weiyang@...il.com>, Balbir Singh <balbirs@...dia.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/4] mm/huge_memory: replace can_split_folio() with
 direct refcount calculation

On 26 Nov 2025, at 4:56, David Hildenbrand (Red Hat) wrote:

>>   static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int new_order,
>>   					     struct page *split_at, struct xa_state *xas,
>>   					     struct address_space *mapping, bool do_lru,
>>   					     struct list_head *list, enum split_type split_type,
>> -					     pgoff_t end, int *nr_shmem_dropped, int extra_pins)
>> +					     pgoff_t end, int *nr_shmem_dropped)
>>   {
>>   	struct folio *end_folio = folio_next(folio);
>>   	struct folio *new_folio, *next;
>> @@ -3782,7 +3773,7 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
>>   	VM_WARN_ON_ONCE(!mapping && end);
>>   	/* Prevent deferred_split_scan() touching ->_refcount */
>>   	ds_queue = folio_split_queue_lock(folio);
>> -	if (folio_ref_freeze(folio, 1 + extra_pins)) {
>> +	if (folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) {
>>   		struct swap_cluster_info *ci = NULL;
>>   		struct lruvec *lruvec;
>>   		int expected_refs;
>> @@ -3853,7 +3844,7 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
>>    			zone_device_private_split_cb(folio, new_folio);
>>  -			expected_refs = folio_expected_ref_count(new_folio) + 1;
>> +			expected_refs = folio_cache_ref_count(new_folio) + 1;
>>   			folio_ref_unfreeze(new_folio, expected_refs);
>>    			if (do_lru)
>> @@ -3897,7 +3888,7 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
>>   		 * Otherwise, a parallel folio_try_get() can grab @folio
>>   		 * and its caller can see stale page cache entries.
>>   		 */
>> -		expected_refs = folio_expected_ref_count(folio) + 1;
>> +		expected_refs = folio_cache_ref_count(folio) + 1;
>>   		folio_ref_unfreeze(folio, expected_refs);
>
> Can we just get rid of the expected_refs variable as well?

OK. Will update it.

>
> Apart from that LGTM, thanks!
>
> Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>

Thanks.

Best Regards,
Yan, Zi