Re: [RFC PATCH 3/6] mm, pgtable: Add ownership for the PTE table - Chih-En Lin

From: Chih-En Lin <shiyn.lin@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Christian Brauner <brauner@kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	William Kucharski <william.kucharski@oracle.com>,
	John Hubbard <jhubbard@nvidia.com>,
	Yunsheng Lin <linyunsheng@huawei.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Suren Baghdasaryan <surenb@google.com>,
	Colin Cross <ccross@google.com>, Feng Tang <feng.tang@intel.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Mike Rapoport <rppt@kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	Daniel Axtens <dja@axtens.net>,
	Jonathan Marek <jonathan@marek.ca>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Pasha Tatashin <pasha.tatashin@soleen.com>,
	Peter Xu <peterx@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andy Lutomirski <luto@kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Fenghua Yu <fenghua.yu@intel.com>,
	David Hildenbrand <david@redhat.com>,
	linux-kernel@vger.kernel.org, Kaiyang Zhao <zhao776@purdue.edu>,
	Huichun Feng <foxhoundsk.tw@gmail.com>,
	Jim Huang <jserv.tw@gmail.com>
Subject: Re: [RFC PATCH 3/6] mm, pgtable: Add ownership for the PTE table
Date: Sat, 21 May 2022 13:01:33 +0800	[thread overview]
Message-ID: <20220521050133.GD1508515@strix-laptop> (raw)
In-Reply-To: <YohkY75ekI6vhMYC@casper.infradead.org>

On Sat, May 21, 2022 at 05:02:43AM +0100, Matthew Wilcox wrote:
> On Fri, May 20, 2022 at 02:31:24AM +0800, Chih-En Lin wrote:
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index 8834e38c06a4..5dcbd7f6c361 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -221,6 +221,7 @@ struct page {
> >  #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
> >  	int _last_cpupid;
> >  #endif
> > +	pmd_t *cow_pte_owner; /* cow pte: pmd */
> 
> This is definitely the wrong place.  I think it could replace _pt_pad_1,
> since it's a pointer to a PMD and so the bottom bit will definitely
> be clear.
>

I will figure out how to use _pt_pad_1.
It seems relative to the compound page (or folio?).

Thanks.