Messages in this thread | | | From | Anshuman Khandual <> | Subject | Re: [RFC/RFT PATCH 0/3] arm64: drop pfn_valid_within() and simplify pfn_valid() | Date | Thu, 8 Apr 2021 10:49:02 +0530 |
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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.
> 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.
> > 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/
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