linux-kernel - Re: [PATCH v2 1/2] mm: clear pte for folios that are zero filled

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Date: Tue, 4 Jun 2024 13:42:25 +0100
From: Usama Arif <usamaarif642@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, yosryahmed@...gle.com,
 nphamcs@...il.com, chengming.zhou@...ux.dev, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v2 1/2] mm: clear pte for folios that are zero filled


On 04/06/2024 13:18, Matthew Wilcox wrote:
> On Tue, Jun 04, 2024 at 11:58:24AM +0100, Usama Arif wrote:
>> +++ b/mm/rmap.c
>> @@ -1819,96 +1819,101 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>   			 */
>>   			dec_mm_counter(mm, mm_counter(folio));
>>   		} else if (folio_test_anon(folio)) {
>> -			swp_entry_t entry = page_swap_entry(subpage);
>> -			pte_t swp_pte;
>> -			/*
>> -			 * Store the swap location in the pte.
>> -			 * See handle_pte_fault() ...
>> -			 */
>> -			if (unlikely(folio_test_swapbacked(folio) !=
>> -					folio_test_swapcache(folio))) {
>> +			if (flags & TTU_ZERO_FOLIO) {
>> +				pte_clear(mm, address, pvmw.pte);
>> +				dec_mm_counter(mm, MM_ANONPAGES);
>> +			} else {
> This is very hard to review.  Is what you've done the same as:
>
> 			if (flags & TTU_ZERO_FOLIO) {
> 				pte_clear(mm, address, pvmw.pte);
> 				dec_mm_counter(mm, MM_ANONPAGES);
> 				goto discard;
> 			}
>
> ?  I genuinely can't tell.
>
Yes, thats what I am doing, will switch to above in next revision, Thanks!