Re: [PATCH v1 02/11] mm/page_alloc: split prep_compound_page into head and tail subparts

[Joao Martins <joao.m.martins@oracle.com>]

On 4/24/21 1:16 AM, Dan Williams wrote:
> On Thu, Mar 25, 2021 at 4:10 PM Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>> Split the utility function prep_compound_page() into head and tail
>> counterparts, and use them accordingly.
> 
> To make this patch stand alone better lets add another sentence:
> 
> "This is in preparation for sharing the storage for / deduplicating
> compound page metadata."
> 
Yeap, I've fixed it up.

> Other than that, looks good to me.
> 
/me nods

>>
>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>> ---
>>  mm/page_alloc.c | 32 +++++++++++++++++++++-----------
>>  1 file changed, 21 insertions(+), 11 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index c53fe4fa10bf..43dd98446b0b 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -692,24 +692,34 @@ void free_compound_page(struct page *page)
>>         __free_pages_ok(page, compound_order(page), FPI_NONE);
>>  }
>>
>> +static void prep_compound_head(struct page *page, unsigned int order)
>> +{
>> +       set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
>> +       set_compound_order(page, order);
>> +       atomic_set(compound_mapcount_ptr(page), -1);
>> +       if (hpage_pincount_available(page))
>> +               atomic_set(compound_pincount_ptr(page), 0);
>> +}
>> +
>> +static void prep_compound_tail(struct page *head, int tail_idx)
>> +{
>> +       struct page *p = head + tail_idx;
>> +
>> +       set_page_count(p, 0);
>> +       p->mapping = TAIL_MAPPING;
>> +       set_compound_head(p, head);
>> +}
>> +
>>  void prep_compound_page(struct page *page, unsigned int order)
>>  {
>>         int i;
>>         int nr_pages = 1 << order;
>>
>>         __SetPageHead(page);
>> -       for (i = 1; i < nr_pages; i++) {
>> -               struct page *p = page + i;
>> -               set_page_count(p, 0);
>> -               p->mapping = TAIL_MAPPING;
>> -               set_compound_head(p, page);
>> -       }
>> +       for (i = 1; i < nr_pages; i++)
>> +               prep_compound_tail(page, i);
>>
>> -       set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
>> -       set_compound_order(page, order);
>> -       atomic_set(compound_mapcount_ptr(page), -1);
>> -       if (hpage_pincount_available(page))
>> -               atomic_set(compound_pincount_ptr(page), 0);
>> +       prep_compound_head(page, order);
>>  }
>>
>>  #ifdef CONFIG_DEBUG_PAGEALLOC
>> --
>> 2.17.1
>>
> 
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