linux-kernel - Re: [PATCH 1/2] mm: pgtable: add missing flag and statistics for kernel PTE page

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Date: Sun, 4 Feb 2024 13:15:24 +0100
From: Mike Rapoport <rppt@...nel.org>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: akpm@...ux-foundation.org, arnd@...db.de, muchun.song@...ux.dev,
	david@...hat.com, willy@...radead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: pgtable: add missing flag and statistics for
 kernel PTE page

On Sun, Feb 04, 2024 at 07:39:38PM +0800, Qi Zheng wrote:
> Hi Mike,
> 
> On 2024/2/4 18:58, Mike Rapoport wrote:
> > On Thu, Feb 01, 2024 at 04:05:40PM +0800, Qi Zheng wrote:
> > > For kernel PTE page, we do not need to allocate and initialize its split
> > > ptlock, but as a page table page, it's still necessary to add PG_table
> > > flag and NR_PAGETABLE statistics for it.
> > > 
> > > Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> > > ---
> > >   include/asm-generic/pgalloc.h |  7 ++++++-
> > >   include/linux/mm.h            | 21 ++++++++++++++++-----
> > >   2 files changed, 22 insertions(+), 6 deletions(-)
> > 
> > This should also update the architectures that define
> > __HAVE_ARCH_PTE_ALLOC_ONE_KERNEL, otherwise NR_PAGETABLE counts will get
> > wrong.
> 
> Yes, this patchset only focuses on the generic implementation. For those
> architectures that define __HAVE_ARCH_PTE_ALLOC_ONE_KERNEL, some reuse
> the generic __pte_alloc_one_kernel(), but some have their own customized
> implementations, which indeed need to be fixed.
> 
> I wasn't familiar with those architectures and didn't investigate why
> they couldn't reuse the generic __pte_alloc_one_kernel(), so I didn't
> fix them.

But with your patch NR_PAGETABLE will underflow e.g. on arm and it'd be a
regression for no good reason.

> It would be better if there are maintainers corresponding to
> the architecture who can help fix it. After all, they have a better
> understanding of the historical background and have a testing
> environment. ;)

-- 
Sincerely yours,
Mike.