linux-kernel - Re: [RFC PATCH v3 1/3] mm: Factor out the pagetable pages account into new helper function

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Date:   Fri, 1 Jul 2022 16:00:59 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     akpm@...ux-foundation.org, willy@...radead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 1/3] mm: Factor out the pagetable pages account
 into new helper function



On 6/30/2022 10:11 PM, Mike Rapoport wrote:
> On Thu, Jun 30, 2022 at 07:11:14PM +0800, Baolin Wang wrote:
>> Factor out the pagetable pages account into new helper functions to avoid
>> duplicated code. Meanwhile these helper functions also will be used to
>> account pagetable pages which do not need split pagetale lock.
>>
>> Meanwhile convert to use mod_lruvec_page_state() in case of non-order-0
>> page table allocation.
> 
> These are *very* rare. I think only parisc may have non-order-0 pmd and pud
> tables.

s390 also has non-order-0 page table allocation, but they both do not 
use the generic page table allocation now.

> With that, I'd suggest making use of compound_nr() build time opt-in.

After more thinking, I'd prefer to change back to use 
inc_lruvec_page_state()/dec_lruvec_page_state(), since now no 
architecures will need non-order-0 page table allocation.

After this patchset, I plan to convert parisc and s390 to use generic 
pagetable allocation, then I will add non-order-0 page table allocation 
support. Like Matthew suggested, maybe I need change the API to pass the 
number of pages.

>> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> ---
>>   include/linux/mm.h | 24 ++++++++++++++++--------
>>   1 file changed, 16 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index a2270e3..3be6d2c 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2353,20 +2353,30 @@ static inline void pgtable_init(void)
>>   	pgtable_cache_init();
>>   }
>>   
>> +static inline void pgtable_page_inc(struct page *page)
>> +{
>> +	__SetPageTable(page);
>> +	mod_lruvec_page_state(page, NR_PAGETABLE, compound_nr(page));
>> +}
>> +
>> +static inline void pgtable_page_dec(struct page *page)
>> +{
>> +	__ClearPageTable(page);
>> +	mod_lruvec_page_state(page, NR_PAGETABLE, -compound_nr(page));
>> +}
>> +
>>   static inline bool pgtable_pte_page_ctor(struct page *page)
>>   {
>>   	if (!ptlock_init(page))
>>   		return false;
>> -	__SetPageTable(page);
>> -	inc_lruvec_page_state(page, NR_PAGETABLE);
>> +	pgtable_page_inc(page);
>>   	return true;
>>   }
>>   
>>   static inline void pgtable_pte_page_dtor(struct page *page)
>>   {
>>   	ptlock_free(page);
>> -	__ClearPageTable(page);
>> -	dec_lruvec_page_state(page, NR_PAGETABLE);
>> +	pgtable_page_dec(page);
>>   }
>>   
>>   #define pte_offset_map_lock(mm, pmd, address, ptlp)	\
>> @@ -2452,16 +2462,14 @@ static inline bool pgtable_pmd_page_ctor(struct page *page)
>>   {
>>   	if (!pmd_ptlock_init(page))
>>   		return false;
>> -	__SetPageTable(page);
>> -	inc_lruvec_page_state(page, NR_PAGETABLE);
>> +	pgtable_page_inc(page);
>>   	return true;
>>   }
>>   
>>   static inline void pgtable_pmd_page_dtor(struct page *page)
>>   {
>>   	pmd_ptlock_free(page);
>> -	__ClearPageTable(page);
>> -	dec_lruvec_page_state(page, NR_PAGETABLE);
>> +	pgtable_page_dec(page);
>>   }
>>   
>>   /*
>> -- 
>> 1.8.3.1
>>
>