linux-kernel - Re: [PATCH 2/2] mm/thp: Rename pmd_mknotpresent() as pmd

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Date:   Tue, 21 Apr 2020 08:07:05 +0100
From:   Will Deacon <will@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, Vineet Gupta <vgupta@...opsys.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        nouveau@...ts.freedesktop.org, linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm/thp: Rename pmd_mknotpresent() as pmd_mknotvalid()

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@...nel.org>

Will