linux-kernel - Re: [PATCH v2 06/10] mm: memory: use a folio in zap_pte

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Date:   Mon, 6 Nov 2023 10:30:59 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        David Hildenbrand <david@...hat.com>,
        <linux-s390@...r.kernel.org>
Subject: Re: [PATCH v2 06/10] mm: memory: use a folio in zap_pte_range()



On 2023/11/5 1:20, Matthew Wilcox wrote:
> On Sat, Nov 04, 2023 at 11:55:18AM +0800, Kefeng Wang wrote:
>> -/* Decides whether we should zap this page with the page pointer specified */
>> -static inline bool should_zap_page(struct zap_details *details, struct page *page)
>> +/* Decides whether we should zap this folio with the folio pointer specified */
>> +static inline bool should_zap_page(struct zap_details *details, struct folio *folio)
> 
> Surely we should rename this to should_zap_folio()?
Will update.
> 
>> @@ -1487,10 +1492,10 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>>   			 * see zap_install_uffd_wp_if_needed().
>>   			 */
>>   			WARN_ON_ONCE(!vma_is_anonymous(vma));
>> -			rss[mm_counter(page)]--;
>> +			rss[mm_counter(&folio->page)]--;
>>   			if (is_device_private_entry(entry))
>> -				page_remove_rmap(page, vma, false);
>> -			put_page(page);
>> +				page_remove_rmap(&folio->page, vma, false);
>> +			folio_put(folio);
> 
> This is wrong.  If we have a PTE-mapped THP, you'll remove the head page
> N times instead of removing each of N pages.

This is device private entry, I suppose that it won't be a THP and large 
folio when check migrate_vma_check_page() and migrate_vma_insert_page(),
right?

> 
> I suspect you're going to collide with Ryan's work by doing this ...
> 
Maybe not if the above is true, at least for now.

Thanks.