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

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Message-ID: <YsAaxFg7w3OpY7eE@linux.ibm.com>
Date:   Sat, 2 Jul 2022 13:15:46 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     akpm@...ux-foundation.org, willy@...radead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 1/3] mm: Factor out the pagetable pages account
 into new helper function

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.
 
> > > Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> > > ---

-- 
Sincerely yours,
Mike.