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

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Date:   Tue, 13 Jun 2023 09:53:03 +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 2023/6/12 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.

> 
>> @@ -1132,30 +1137,30 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>>   			 * and it's on LRU. It can only be a THP so the order
>>   			 * is safe to read and it's 0 for tail pages.
>>   			 */
> 
> ^^^ This comment needs to be updated too.
will update
> 
>> -		mod_node_page_state(page_pgdat(page),
>> -				NR_ISOLATED_ANON + page_is_file_lru(page),
>> -				thp_nr_pages(page));
>> +		lruvec_del_folio(lruvec, folio);
>> +		mod_node_page_state(folio_pgdat(folio),
>> +				NR_ISOLATED_ANON + folio_is_file_lru(folio),
>> +				folio_nr_pages(folio));
> 
> 		node_stat_mod_folio()
> ok

Thanks


>