linux-kernel - Re: [RFC PATCH v3 2/3] mm: Add PUD level pagetable account

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Date:   Sun, 3 Jul 2022 22:49:56 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 2/3] mm: Add PUD level pagetable account



On 7/3/2022 10:28 PM, Mike Rapoport wrote:
> On Sun, Jul 03, 2022 at 10:06:32PM +0800, Baolin Wang wrote:
>>
>>
>> On 7/3/2022 11:40 AM, Matthew Wilcox wrote:
>>> On Fri, Jul 01, 2022 at 04:04:21PM +0800, Baolin Wang wrote:
>>>>> Using pgtable_pud_page_ctor() and pgtable_pud_page_dtor() would be
>>>>> consistent with what we currently have for PTEs and PMDs.
>>>>>
>>>>> This applies to all the additions of pgtable_page_dec() and
>>>>> pgtable_page_inc().
>>>>
>>>> OK. I can add pgtable_pud_page_ctor() and pgtable_pud_page_dtor() helpers to
>>>> keep consistent, which are just wrappers of pgtable_page_inc() and
>>>> pgtable_page_dec().
>>>
>>> I think you misunderstand Mike.
>>>
>>> Don't add pgtable_page_inc() and pgtable_page_dec().  Just add
>>> pgtable_pud_page_ctor() and pgtable_pud_page_dtor().  At least, that
>>> was what I said last time you posted these patches.
>>
>> My concern is that I need another helpers for kernel page table allocation
>> helpers, if only adding pgtable_pud_page_ctor() and pgtable_pud_page_dtor()
>> like below:
>>
>> static inline void pgtable_pud_page_ctor(struct page *page)
>> {
>> 	__SetPageTable(page);
>> 	inc_lruvec_page_state(page, NR_PAGETABLE);
>> }
>>
>> static inline void pgtable_pud_page_dtor(struct page *page)
>> {
>> 	__ClearPageTable(page);
>> 	dec_lruvec_page_state(page, NR_PAGETABLE);
>> }
>>
>> So for kernel pte page table allocation, I need another similar helpers like
>> below. However they do the samething with
>> pgtable_pud_page_ctor/pgtable_pud_page_dtor, so I am not sure this is good
>> for adding these duplicate code.
>>
>> static inline void pgtable_kernel_pte_page_ctor(struct page *page)
>> {
>> 	__SetPageTable(page);
>> 	inc_lruvec_page_state(page, NR_PAGETABLE);
>> }
>>
>> static inline void pgtable_kernel_pte_page_dtor(struct page *page)
>> {
>> 	__ClearPageTable(page);
>> 	dec_lruvec_page_state(page, NR_PAGETABLE);
>> }
>>
>> Instead adding a common helpers seems more readable to me, which can also
>> simplify original pgtable_pmd_page_dtor()/pgtable_pmd_page_ctor(). Something
>> like below.
>>
>> static inline void pgtable_page_inc(struct page *page)
>> {
>> 	__SetPageTable(page);
>> 	inc_lruvec_page_state(page, NR_PAGETABLE);
>> }
>>
>> static inline void pgtable_page_dec(struct page *page)
>> {
>> 	__ClearPageTable(page);
>> 	dec_lruvec_page_state(page, NR_PAGETABLE);
>> }
>>
>> static inline void pgtable_pud_page_ctor(struct page *page)
>> {
>> 	pgtable_page_inc(page);
>> }
>>
>> static inline void pgtable_pud_page_dtor(struct page *page)
>> {
>> 	pgtable_page_dec(page);
>> }
>>
>> For kernel pte page table, we can just use
>> pgtable_page_inc/pgtable_page_dec(), or adding
>> pgtable_kernel_pte_page_ctor/pgtable_kernel_pte_page_dtor, which just
>> wrappers of pgtable_page_inc() and pgtable_page_dec().
>>
>> Matthew and Mike, how do you think? Thanks.
> 
> I actually meant to add pgtable_pud_page_ctor/dtor() as a wrapper for the
> new helper to keep pud tables allocation consistent with pmd and pte and
> as a provision for the time we'll have per-page pud locks.
> 
> For the accounting of the kernel page tables a new helper does make sense
> because there are no locks to initialize for the kernel page tables.

Thanks for clarification. That is also my thought.

> 
> I can't say that I'm happy with the pgtable_page_inc/dec names, though.
> 
> Maybe page_{set,clear}_pgtable()?

Sounds better than pgtable_page_inc/dec() for me. I will use them in 
next version if no other objections. Thanks.