From: Mike Rapoport <rppt@kernel.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
Ard Biesheuvel <ardb@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
David Hildenbrand <david@redhat.com>,
Marc Zyngier <maz@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Mike Rapoport <rppt@linux.ibm.com>, Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, James Morse <james.morse@arm.com>
Subject: Re: [RFC/RFT PATCH 0/3] arm64: drop pfn_valid_within() and simplify pfn_valid()
Date: Thu, 8 Apr 2021 09:27:53 +0300 [thread overview]
Message-ID: <YG6iaZJI/RiUwXzv@kernel.org> (raw)
In-Reply-To: <2f68ea11-7c56-1c55-f0be-3aad7188c00a@arm.com>
On Thu, Apr 08, 2021 at 10:49:02AM +0530, Anshuman Khandual wrote:
> Adding James here.
>
> + James Morse <james.morse@arm.com>
>
> On 4/7/21 10:56 PM, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> >
> > Hi,
> >
> > These patches aim to remove CONFIG_HOLES_IN_ZONE and essentially hardwire
> > pfn_valid_within() to 1.
>
> That would be really great for arm64 platform as it will save CPU cycles on
> many generic MM paths, given that our pfn_valid() has been expensive.
>
> >
> > The idea is to mark NOMAP pages as reserved in the memory map and restore
>
> Though I am not really sure, would that possibly be problematic for UEFI/EFI
> use cases as it might have just treated them as normal struct pages till now.
I don't think there should be a problem because now the struct pages for
UEFI/ACPI never got to be used by the core mm. They were (rightfully)
skipped by memblock_free_all() from one side and pfn_valid() and
pfn_valid_within() return false for them in various pfn walkers from the
other side.
> > the intended semantics of pfn_valid() to designate availability of struct
> > page for a pfn.
>
> Right, that would be better as the current semantics is not ideal.
>
> >
> > With this the core mm will be able to cope with the fact that it cannot use
> > NOMAP pages and the holes created by NOMAP ranges within MAX_ORDER blocks
> > will be treated correctly even without the need for pfn_valid_within.
> >
> > The patches are only boot tested on qemu-system-aarch64 so I'd really
> > appreciate memory stress tests on real hardware.
>
> Did some preliminary memory stress tests on a guest with portions of memory
> marked as MEMBLOCK_NOMAP and did not find any obvious problem. But this might
> require some testing on real UEFI environment with firmware using MEMBLOCK_NOMAP
> memory to make sure that changing these struct pages to PageReserved() is safe.
I surely have no access for such machines :)
> > If this actually works we'll be one step closer to drop custom pfn_valid()
> > on arm64 altogether.
>
> Right, planning to rework and respin the RFC originally sent last month.
>
> https://patchwork.kernel.org/project/linux-mm/patch/1615174073-10520-1-git-send-email-anshuman.khandual@arm.com/
--
Sincerely yours,
Mike.
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prev parent reply other threads:[~2021-04-08 6:29 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-07 17:26 [RFC/RFT PATCH 0/3] arm64: drop pfn_valid_within() and simplify pfn_valid() Mike Rapoport
2021-04-07 17:26 ` [RFC/RFT PATCH 1/3] memblock: update initialization of reserved pages Mike Rapoport
2021-04-08 5:16 ` Anshuman Khandual
2021-04-08 5:48 ` Mike Rapoport
2021-04-14 15:12 ` David Hildenbrand
2021-04-14 15:27 ` Ard Biesheuvel
2021-04-14 15:52 ` David Hildenbrand
2021-04-14 20:24 ` Mike Rapoport
2021-04-15 9:30 ` David Hildenbrand
2021-04-16 11:44 ` Mike Rapoport
2021-04-16 11:54 ` David Hildenbrand
2021-04-14 20:11 ` Mike Rapoport
2021-04-14 20:06 ` Mike Rapoport
2021-04-07 17:26 ` [RFC/RFT PATCH 2/3] arm64: decouple check whether pfn is normal memory from pfn_valid() Mike Rapoport
2021-04-08 5:14 ` Anshuman Khandual
2021-04-08 6:00 ` Mike Rapoport
2021-04-14 15:58 ` David Hildenbrand
2021-04-14 20:29 ` Mike Rapoport
2021-04-15 9:31 ` David Hildenbrand
2021-04-16 11:40 ` Mike Rapoport
2021-04-07 17:26 ` [RFC/RFT PATCH 3/3] arm64: drop pfn_valid_within() and simplify pfn_valid() Mike Rapoport
2021-04-08 5:12 ` Anshuman Khandual
2021-04-08 6:17 ` Mike Rapoport
2021-04-08 5:19 ` [RFC/RFT PATCH 0/3] " Anshuman Khandual
2021-04-08 6:27 ` Mike Rapoport [this message]
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