Re: [PATCH 2/3] mm: pgtable: add missing pt_index to struct ptdesc

Qi Zheng
2024-03-27T02:06:17Z

On 2024/3/27 03:25, Vishal Moola wrote:
> On Mon, Mar 04, 2024 at 07:07:19PM +0800, Qi Zheng wrote:
>> In s390, the page->index field is used for gmap (see gmap_shadow_pgt()),
>> so add the corresponding pt_index to struct ptdesc and add a comment to
>> clarify this.
>
> Yes s390 gmap 'uses' page->index, but not for the purpose page->index is
> supposed to hold. It's alright to have a variable here, but I'd rather
> see it named something more appropriate to the purporse it serves.

Make sense.

>
> You can take look at this patch from v5 of my ptdesc conversion series
> for more info:
> https://lore.kernel.org/linux-mm/20230622205745.79707-3-vishal.moola@gmail.com/

Oh, but it seems that this patch has not been merged?

>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>> include/linux/mm_types.h | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
>> index 5ea77969daae..5240bd7bca33 100644
>> --- a/include/linux/mm_types.h
>> +++ b/include/linux/mm_types.h
>> @@ -425,6 +425,7 @@ FOLIO_MATCH(compound_head, _head_2a);
>> * @_pt_pad_1: Padding that aliases with page's compound head.
>> * @pmd_huge_pte: Protected by ptdesc->ptl, used for THPs.
>> * @__page_mapping: Aliases with page->mapping. Unused for page tables.
>> + * @pt_index: Used for s390 gmap.
>> * @pt_mm: Used for x86 pgds.
>> * @pt_frag_refcount: For fragmented page table tracking. Powerpc only.
>> * @_pt_pad_2: Padding to ensure proper alignment.
>> @@ -450,6 +451,7 @@ struct ptdesc {
>> unsigned long __page_mapping;
>>
>> union {
>> + pgoff_t pt_index;
>> struct mm_struct *pt_mm;
>> atomic_t pt_frag_refcount;
>> };
>> @@ -475,6 +477,7 @@ TABLE_MATCH(flags, __page_flags);
>> TABLE_MATCH(compound_head, pt_list);
>> TABLE_MATCH(compound_head, _pt_pad_1);
>> TABLE_MATCH(mapping, __page_mapping);
>> +TABLE_MATCH(index, pt_index);
>> TABLE_MATCH(rcu_head, pt_rcu_head);
>> TABLE_MATCH(page_type, __page_type);
>> TABLE_MATCH(_refcount, __page_refcount);
>> --
>> 2.30.2
>>