Re: [PATCH 2/2] mm/thp: Rename pmd_mknotpresent() as pmd_mknotvalid()

From: Will Deacon <will@kernel.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: linux-mm@kvack.org, Vineet Gupta <vgupta@synopsys.com>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	nouveau@lists.freedesktop.org,
	linux-snps-arc@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] mm/thp: Rename pmd_mknotpresent() as pmd_mknotvalid()
Date: Tue, 21 Apr 2020 08:07:05 +0100	[thread overview]
Message-ID: <20200421070703.GC14448@willie-the-truck> (raw)
In-Reply-To: <78fee884-78fc-6102-1a37-12106dc21336@arm.com>

On Tue, Apr 21, 2020 at 04:57:26AM +0530, Anshuman Khandual wrote:
> 
> 
> On 04/21/2020 02:33 AM, Will Deacon wrote:
> > On Fri, Mar 20, 2020 at 10:24:17AM +0530, Anshuman Khandual wrote:
> >> pmd_present() is expected to test positive after pmdp_mknotpresent() as the
> >> PMD entry still points to a valid huge page in memory. pmdp_mknotpresent()
> >> implies that given PMD entry is just invalidated from MMU perspective while
> >> still holding on to pmd_page() referred valid huge page thus also clearing
> >> pmd_present() test. This creates the following situation which is counter
> >> intuitive.
> >>
> >> [pmd_present(pmd_mknotpresent(pmd)) = true]
> >>
> >> This renames pmd_mknotpresent() as pmd_mknotvalid() reflecting the helper's
> >> functionality more accurately while changing the above mentioned situation
> >> as follows. This does not create any functional change.
> >>
> >> [pmd_present(pmd_mknotvalid(pmd)) = true]
> >>
> >> This is not applicable for platforms that define own pmdp_invalidate() via
> >> __HAVE_ARCH_PMDP_INVALIDATE. Suggestion for renaming came during a previous
> >> discussion here.
> > 
> > Bikeshed alert: maybe pmd_mkinvalid() would be better, given that this is
> > a one-trick pony for pmdp_invalidate()?
> 
> I had thought about making it pmd_mkinvalid() earlier. But as we were replacing
> pmd_mknotpresent(), hence went with similar pattern pmd_mknotvalid() which was
> originally suggested by Catalin. There is an existing pte_mknotpresent() in arc
> platform as well. I dont have a very strong opinion either way, will be happy
> to rename. But then still wondering if we really need to.

I just think that having pmdp_invalidate() call pmd_mkinvalid() makes a lot
of sense and, since this is a pure renaming patch, then that's worth taking
into consideration.

If you go with pmd_mkinvalid(), then:

Acked-by: Will Deacon <will@kernel.org>

Will