Re: [PATCH -next v2 1/2] mm: compaction: convert to use a folio in isolate_migratepages_block()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2023/6/21 14:20, Baolin Wang wrote:
> Hi
> 
> On 6/19/2023 7:07 PM, Kefeng Wang wrote:
>> Directly use a folio instead of page_folio() when page successfully
>> isolated (hugepage and movable page) and after folio_get_nontail_page(),
>> which removes several calls to compound_head().
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>> ---
>> v2:
>> - update comments and use node_stat_mod_folio, per Matthew Wilcox
>> - add missed PageLRU conversion and rebase on next-20230619
>>
>>   mm/compaction.c | 84 ++++++++++++++++++++++++++-----------------------
>>   1 file changed, 44 insertions(+), 40 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 6149a2d324be..0334eefe4bfa 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -795,6 +795,7 @@ isolate_migratepages_block(struct compact_control 
>> *cc, unsigned long low_pfn,
>>       struct lruvec *lruvec;
>>       unsigned long flags = 0;
>>       struct lruvec *locked = NULL;
>> +    struct folio *folio = NULL;
>>       struct page *page = NULL, *valid_page = NULL;
>>       struct address_space *mapping;
>>       unsigned long start_pfn = low_pfn;
>> @@ -891,7 +892,7 @@ isolate_migratepages_block(struct compact_control 
>> *cc, unsigned long low_pfn,
>>           if (!valid_page && pageblock_aligned(low_pfn)) {
>>               if (!isolation_suitable(cc, page)) {
>>                   low_pfn = end_pfn;
>> -                page = NULL;
>> +                folio = NULL;
>>                   goto isolate_abort;
>>               }
>>               valid_page = page;
>> @@ -923,7 +924,8 @@ 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;
>>               }
>> @@ -991,8 +993,10 @@ isolate_migratepages_block(struct compact_control 
>> *cc, unsigned long low_pfn,
>>                       locked = NULL;
>>                   }
>> -                if (isolate_movable_page(page, mode))
>> +                if (isolate_movable_page(page, mode)) {
>> +                    folio = page_folio(page);
>>                       goto isolate_success;
>> +                }
>>               }
>>               goto isolate_fail;
>> @@ -1003,7 +1007,8 @@ isolate_migratepages_block(struct 
>> compact_control *cc, unsigned long low_pfn,
>>            * sure the page is not being freed elsewhere -- the
>>            * page release code relies on it.
>>            */
>> -        if (unlikely(!get_page_unless_zero(page)))
>> +        folio = folio_get_nontail_page(page);
> 
> I'm just curious, how can you make sure the 'page' is not a tail page? 
> Since the validation is lockless.

folio_get_nontail_page is added by commit "3c1ea2c729ef (mm: add
folio_get_nontail_page())", see more comments [1]

[1] https://lore.kernel.org/lkml/Y86sRiKAAOz2myNe@casper.infradead.org/

>