Messages in this thread | | | Subject | Re: [RFC 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory | From | Anshuman Khandual <> | Date | Mon, 25 Jan 2021 11:52:32 +0530 |
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On 12/22/20 12:42 PM, Anshuman Khandual wrote: > pfn_valid() asserts that there is a memblock entry for a given pfn without > MEMBLOCK_NOMAP flag being set. The problem with ZONE_DEVICE based memory is > that they do not have memblock entries. Hence memblock_is_map_memory() will > invariably fail via memblock_search() for a ZONE_DEVICE based address. This > eventually fails pfn_valid() which is wrong. memblock_is_map_memory() needs > to be skipped for such memory ranges. As ZONE_DEVICE memory gets hotplugged > into the system via memremap_pages() called from a driver, their respective > memory sections will not have SECTION_IS_EARLY set. > > Normal hotplug memory will never have MEMBLOCK_NOMAP set in their memblock > regions. Because the flag MEMBLOCK_NOMAP was specifically designed and set > for firmware reserved memory regions. memblock_is_map_memory() can just be > skipped as its always going to be positive and that will be an optimization > for the normal hotplug memory. Like ZONE_DEVIE based memory, all hotplugged > normal memory too will not have SECTION_IS_EARLY set for their sections. > > Skipping memblock_is_map_memory() for all non early memory sections would > fix pfn_valid() problem for ZONE_DEVICE based memory and also improve its > performance for normal hotplug memory as well. > > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: Ard Biesheuvel <ardb@kernel.org> > Cc: Robin Murphy <robin.murphy@arm.com> > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support") > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Hello David/Mike,
Given that we would need to rework early sections, memblock semantics via a new config i.e EARLY_SECTION_MEMMAP_HOLES and also some possible changes to ARCH_KEEP_MEMBLOCK and HAVE_ARCH_PFN_VALID, wondering if these patches here which fixes a problem (and improves performance) can be merged first. After that, I could start working on the proposed rework. Could you please let me know your thoughts on this. Thank you.
- Anshuman
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