From: Michael Ellerman <mpe@ellerman.id.au>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
Andrew Morton <akpm@linux-foundation.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Will Deacon <will.deacon@arm.com>,
Michal Hocko <mhocko@kernel.org>,
linux-mm@kvack.org, Ingo Molnar <mingo@redhat.com>,
linux-arm-kernel@lists.infradead.org,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
linuxppc-dev@lists.ozlabs.org,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH V2] mm/ioremap: Probe platform for p4d huge map support
Date: Fri, 12 Jul 2019 17:07:48 +1000 [thread overview]
Message-ID: <87tvbrennf.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <fbc147c7-bec2-daed-b828-c4ae170010a9@arm.com>
Anshuman Khandual <anshuman.khandual@arm.com> writes:
> On 07/03/2019 04:36 AM, Andrew Morton wrote:
>> On Fri, 28 Jun 2019 10:50:31 +0530 Anshuman Khandual <anshuman.khandual@arm.com> wrote:
>>
>>> Finishing up what the commit c2febafc67734a ("mm: convert generic code to
>>> 5-level paging") started out while levelling up P4D huge mapping support
>>> at par with PUD and PMD. A new arch call back arch_ioremap_p4d_supported()
>>> is being added which just maintains status quo (P4D huge map not supported)
>>> on x86, arm64 and powerpc.
>>
>> Does this have any runtime effects? If so, what are they and why? If
>> not, what's the actual point?
>
> It just finishes up what the previous commit c2febafc67734a ("mm: convert
> generic code to 5-level paging") left off with respect p4d based huge page
> enablement for ioremap. When HAVE_ARCH_HUGE_VMAP is enabled its just a simple
> check from the arch about the support, hence runtime effects are minimal.
The return value of arch_ioremap_p4d_supported() is stored in the
variable ioremap_p4d_capable which is then returned by
ioremap_p4d_enabled().
That is used by ioremap_try_huge_p4d() called from ioremap_p4d_range()
from ioremap_page_range().
The runtime effect is that it prevents ioremap_page_range() from trying
to create huge mappings at the p4d level on arches that don't support
it.
cheers
next prev parent reply other threads:[~2019-07-12 7:17 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-28 5:20 [PATCH V2] mm/ioremap: Probe platform for p4d huge map support Anshuman Khandual
2019-07-02 23:06 ` Andrew Morton
2019-07-04 15:26 ` Anshuman Khandual
2019-07-12 7:07 ` Michael Ellerman [this message]
2019-07-12 8:40 ` Stephen Rothwell
2019-07-12 9:58 ` Anshuman Khandual
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