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

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Date:   Sun, 3 Jul 2022 17:28:15 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.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 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.

I can't say that I'm happy with the pgtable_page_inc/dec names, though.

Maybe page_{set,clear}_pgtable()?

-- 
Sincerely yours,
Mike.