Re: [PATCH v10 2/8] mm/huge_memory: add two new (not yet used) functions for folio_split()

[Zi Yan]

On 10 Mar 2025, at 12:14, Zi Yan wrote:

> On 7 Mar 2025, at 12:39, Zi Yan wrote:
>
>> This is a preparation patch, both added functions are not used yet.
>>
>> The added __split_unmapped_folio() is able to split a folio with its
>> mapping removed in two manners: 1) uniform split (the existing way), and
>> 2) buddy allocator like (or non-uniform) split.
>>
>> The added __split_folio_to_order() can split a folio into any lower order.
>> For uniform split, __split_unmapped_folio() calls it once to split the
>> given folio to the new order. For buddy allocator like (non-uniform)
>> split, __split_unmapped_folio() calls it (folio_order - new_order) times
>> and each time splits the folio containing the given page to one lower
>> order.
>>
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>> Cc: David Hildenbrand <david@xxxxxxxxxx>
>> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
>> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
>> Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
>> Cc: Kirill A. Shuemov <kirill.shutemov@xxxxxxxxxxxxxxx>
>> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
>> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>> Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
>> Cc: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
>> Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
>> Cc: Kairui Song <kasong@xxxxxxxxxxx>
>> ---
>>  mm/huge_memory.c | 348 ++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 347 insertions(+), 1 deletion(-)
>
> Hi Andrew,
>
> The patch below should fix the issues discovered by Hugh. Please fold
> it into this patch. Thank you for all the help.
>

Hi Andrew,

This is the updated version including:
1. Hugh’s fix on unfreezing head folio correctly,
2. Hugh’s fix on drop the right number of refs on tail folio,
3. Matthew’s suggestion on using new_folio instead of new_head and
using i instead of index.