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

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Message-ID: <17df0d3c-caaf-ee34-f702-1d4e7674887f@linux.alibaba.com>
Date:   Sun, 3 Jul 2022 22:06:32 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Mike Rapoport <rppt@...ux.ibm.com>, 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 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 yo uposted 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.