linux-kernel - Re: [PATCH 2/3] mm: pgtable: add missing pt

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Message-ID: <d650b969-ebd7-4821-8d5a-7938ee1b7154@bytedance.com>
Date: Wed, 27 Mar 2024 10:06:06 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Vishal Moola <vishal.moola@...il.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, david@...hat.com,
 rppt@...nel.org, willy@...radead.org, muchun.song@...ux.dev,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm: pgtable: add missing pt_index to struct ptdesc



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@...edance.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
>>