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

[Baolin Wang]

On 7/2/2022 6:15 PM, Mike Rapoport wrote:
> On Fri, Jul 01, 2022 at 04:00:59PM +0800, Baolin Wang wrote:
> > 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.
>
> I think it would be simpler to add proper accounting to s390 and parisc
> versions than make them use the generic allocation functions. Moreover, API
> change to support these cases feels like unnecessary churn to me.

Got it. Thanks.