linux-kernel - Re: [PATCH -next 1/2] mm: compaction: convert to use a folio in isolate_migratepages

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Message-ID: <6acaf695-1c77-c0c6-a1d4-4cc946310997@huawei.com>
Date:   Wed, 14 Jun 2023 19:21:02 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <jgowans@...zon.com>,
        <yuzhao@...gle.com>
Subject: Re: [PATCH -next 1/2] mm: compaction: convert to use a folio in
 isolate_migratepages_block()



On 2023/6/13 9:53, Kefeng Wang wrote:
> 
> 
> On 2023/6/12 22:41, Matthew Wilcox wrote:
>> On Mon, Jun 12, 2023 at 10:34:13PM +0800, Kefeng Wang wrote:
>>> @@ -959,7 +960,8 @@ isolate_migratepages_block(struct compact_control 
>>> *cc, unsigned long low_pfn,
>>>                    * Hugepage was successfully isolated and placed
>>>                    * on the cc->migratepages list.
>>>                    */
>>> -                low_pfn += compound_nr(page) - 1;
>>> +                folio = page_folio(page);
>>> +                low_pfn += folio_nr_pages(folio) - 1;
>>>                   goto isolate_success_no_list;
>>
>> Why is this safe?  That is, how do we know that the folio can't be
>> dissolved under us at this point, then reallocated and hit the
>> VM_BUG_ON_PGFLAGS(PageTail(page), page) in folio_flags() when we
>> test folio_test_large()?
> 
> This is successfully isolated path, after isolate_hugetlb(),  the folio
> reference is incremented, so I think the folio can't be dissolved here,
> correct me if I am wrong.

Hi Matthew，is it enough for the above conversion from page to folio with 
reference?