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

[Baolin Wang]

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.