Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
Message-ID: <e3c275c3-e09d-4495-8132-9464133db283@huawei.com>
Date:   Mon, 6 Nov 2023 10:30:59 +0800
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v2 06/10] mm: memory: use a folio in zap_pte_range()
To:     Matthew Wilcox <willy@infradead.org>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        David Hildenbrand <david@redhat.com>,
        <linux-s390@vger.kernel.org>
References: <20231104035522.2418660-1-wangkefeng.wang@huawei.com>
 <20231104035522.2418660-7-wangkefeng.wang@huawei.com>
 <ZUZ9dg4YHZdUKDqO@casper.infradead.org>
Content-Language: en-US
From:   Kefeng Wang <wangkefeng.wang@huawei.com>
In-Reply-To: <ZUZ9dg4YHZdUKDqO@casper.infradead.org>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


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.