Messages in this thread | | | Subject | Re: [RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes | From | David Hildenbrand <> | Date | Thu, 22 Apr 2021 11:48:58 +0200 |
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On 22.04.21 11:42, Mike Rapoport wrote: > On Thu, Apr 22, 2021 at 11:03:50AM +0200, David Hildenbrand wrote: >> On 22.04.21 09:50, Anshuman Khandual wrote: >>> Platforms like arm and arm64 have redefined pfn_valid() because their early >>> memory sections might have contained memmap holes after freeing parts of it >>> during boot, which should be skipped while validating a pfn for struct page >>> backing. This scenario on certain platforms where memmap is not continuous, >>> could be captured with a new option CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES. >>> Then the generic pfn_valid() can be improved to accommodate such platforms. >>> This reduces overall code footprint and also improves maintainability. >>> >>> free_unused_memmap() and pfn_to_online_page() have been updated to include >>> such cases. This also exports memblock_is_memory() for all drivers that use >>> pfn_valid() but lack required visibility. After the new config is in place, >>> drop CONFIG_HAVE_ARCH_PFN_VALID from arm64 platforms. >>> >>> Cc: Catalin Marinas <catalin.marinas@arm.com> >>> Cc: Will Deacon <will@kernel.org> >>> Cc: Andrew Morton <akpm@linux-foundation.org> >>> Cc: Mike Rapoport <rppt@kernel.org> >>> Cc: David Hildenbrand <david@redhat.com> >>> Cc: linux-arm-kernel@lists.infradead.org >>> Cc: linux-kernel@vger.kernel.org >>> Cc: linux-mm@kvack.org >>> Suggested-by: David Hildenbrand <david@redhat.com> >>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >>> --- >>> This patch applies on the latest mainline kernel after Mike's series >>> regarding arm64 based pfn_valid(). >>> >>> https://lore.kernel.org/linux-mm/20210422061902.21614-1-rppt@kernel.org/T/#t >>> >>> Changes in RFC V2: >>> >>> - Dropped support for arm (32 bit) >>> - Replaced memblock_is_map_memory() check with memblock_is_memory() >>> - MEMBLOCK_NOMAP memory are no longer skipped for pfn_valid() >>> - Updated pfn_to_online_page() per David >>> - Updated free_unused_memmap() to preserve existing semantics per Mike >>> - Exported memblock_is_memory() instead of memblock_is_map_memory() >>> >>> Changes in RFC V1: >>> >>> - https://patchwork.kernel.org/project/linux-mm/patch/1615174073-10520-1-git-send-email-anshuman.khandual@arm.com/ >>> >>> arch/arm64/Kconfig | 2 +- >>> arch/arm64/include/asm/page.h | 1 - >>> arch/arm64/mm/init.c | 41 ----------------------------------- >>> include/linux/mmzone.h | 18 ++++++++++++++- >>> mm/Kconfig | 9 ++++++++ >>> mm/memblock.c | 8 +++++-- >>> mm/memory_hotplug.c | 5 +++++ >>> 7 files changed, 38 insertions(+), 46 deletions(-) >>> >>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >>> index b4a9b493ce72..4cdc3570ffa9 100644 >>> --- a/arch/arm64/Kconfig >>> +++ b/arch/arm64/Kconfig >>> @@ -144,7 +144,6 @@ config ARM64 >>> select HAVE_ARCH_KGDB >>> select HAVE_ARCH_MMAP_RND_BITS >>> select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT >>> - select HAVE_ARCH_PFN_VALID >>> select HAVE_ARCH_PREL32_RELOCATIONS >>> select HAVE_ARCH_SECCOMP_FILTER >>> select HAVE_ARCH_STACKLEAK >>> @@ -167,6 +166,7 @@ config ARM64 >>> if $(cc-option,-fpatchable-function-entry=2) >>> select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \ >>> if DYNAMIC_FTRACE_WITH_REGS >>> + select HAVE_EARLY_SECTION_MEMMAP_HOLES >>> select HAVE_EFFICIENT_UNALIGNED_ACCESS >>> select HAVE_FAST_GUP >>> select HAVE_FTRACE_MCOUNT_RECORD >>> diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h >>> index 75ddfe671393..fcbef3eec4b2 100644 >>> --- a/arch/arm64/include/asm/page.h >>> +++ b/arch/arm64/include/asm/page.h >>> @@ -37,7 +37,6 @@ void copy_highpage(struct page *to, struct page *from); >>> typedef struct page *pgtable_t; >>> -int pfn_valid(unsigned long pfn); >>> int pfn_is_map_memory(unsigned long pfn); >>> #include <asm/memory.h> >>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c >>> index f431b38d0837..5731a11550d8 100644 >>> --- a/arch/arm64/mm/init.c >>> +++ b/arch/arm64/mm/init.c >>> @@ -217,47 +217,6 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max) >>> free_area_init(max_zone_pfns); >>> } >>> -int pfn_valid(unsigned long pfn) >>> -{ >>> - phys_addr_t addr = PFN_PHYS(pfn); >>> - >>> - /* >>> - * Ensure the upper PAGE_SHIFT bits are clear in the >>> - * pfn. Else it might lead to false positives when >>> - * some of the upper bits are set, but the lower bits >>> - * match a valid pfn. >>> - */ >>> - if (PHYS_PFN(addr) != pfn) >>> - return 0; >>> - >>> -#ifdef CONFIG_SPARSEMEM >>> -{ >>> - struct mem_section *ms; >>> - >>> - if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS) >>> - return 0; >>> - >>> - ms = __pfn_to_section(pfn); >>> - if (!valid_section(ms)) >>> - return 0; >>> - >>> - /* >>> - * ZONE_DEVICE memory does not have the memblock entries. >>> - * memblock_is_memory() check for ZONE_DEVICE based >>> - * addresses will always fail. Even the normal hotplugged >>> - * memory will never have MEMBLOCK_NOMAP flag set in their >>> - * memblock entries. Skip memblock search for all non early >>> - * memory sections covering all of hotplug memory including >>> - * both normal and ZONE_DEVICE based. >>> - */ >>> - if (!early_section(ms)) >>> - return pfn_section_valid(ms, pfn); >>> -} >>> -#endif >>> - return memblock_is_memory(addr); >>> -} >>> -EXPORT_SYMBOL(pfn_valid); >>> - >>> int pfn_is_map_memory(unsigned long pfn) >>> { >>> phys_addr_t addr = PFN_PHYS(pfn); >>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >>> index 961f0eeefb62..18bf71665211 100644 >>> --- a/include/linux/mmzone.h >>> +++ b/include/linux/mmzone.h >>> @@ -1421,10 +1421,22 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) >>> * >>> * Return: 1 for PFNs that have memory map entries and 0 otherwise >>> */ >>> +bool memblock_is_memory(phys_addr_t addr); >>> + >>> static inline int pfn_valid(unsigned long pfn) >>> { >>> + phys_addr_t addr = PFN_PHYS(pfn); >>> struct mem_section *ms; >>> + /* >>> + * Ensure the upper PAGE_SHIFT bits are clear in the >>> + * pfn. Else it might lead to false positives when >>> + * some of the upper bits are set, but the lower bits >>> + * match a valid pfn. >>> + */ >>> + if (PHYS_PFN(addr) != pfn) >>> + return 0; >>> + >>> if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS) >>> return 0; >>> ms = __nr_to_section(pfn_to_section_nr(pfn)); >>> @@ -1434,7 +1446,11 @@ static inline int pfn_valid(unsigned long pfn) >>> * Traditionally early sections always returned pfn_valid() for >>> * the entire section-sized span. >>> */ >>> - return early_section(ms) || pfn_section_valid(ms, pfn); >>> + if (early_section(ms)) >>> + return IS_ENABLED(CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES) ? >>> + memblock_is_memory(pfn << PAGE_SHIFT) : 1; >>> + >>> + return pfn_section_valid(ms, pfn); >>> } >>> #endif >>> diff --git a/mm/Kconfig b/mm/Kconfig >>> index 24c045b24b95..db7128111874 100644 >>> --- a/mm/Kconfig >>> +++ b/mm/Kconfig >>> @@ -135,6 +135,15 @@ config HAVE_FAST_GUP >>> config ARCH_KEEP_MEMBLOCK >>> bool >>> +config HAVE_EARLY_SECTION_MEMMAP_HOLES >>> + depends on ARCH_KEEP_MEMBLOCK && SPARSEMEM_VMEMMAP >>> + def_bool n >>> + help >>> + Early sections on certain platforms might have some memory ranges that >>> + are not backed with struct page mappings. When subscribed, this option >>> + enables special handling for those memory ranges in certain situations >>> + such as pfn_valid(). >>> + >>> # Keep arch NUMA mapping infrastructure post-init. >>> config NUMA_KEEP_MEMINFO >>> bool >>> diff --git a/mm/memblock.c b/mm/memblock.c >>> index 3abf2c3fea7f..93f8a9c8428d 100644 >>> --- a/mm/memblock.c >>> +++ b/mm/memblock.c >>> @@ -1740,6 +1740,7 @@ bool __init_memblock memblock_is_memory(phys_addr_t addr) >>> { >>> return memblock_search(&memblock.memory, addr) != -1; >>> } >>> +EXPORT_SYMBOL(memblock_is_memory); >>> bool __init_memblock memblock_is_map_memory(phys_addr_t addr) >>> { >>> @@ -1931,8 +1932,11 @@ static void __init free_unused_memmap(void) >>> unsigned long start, end, prev_end = 0; >>> int i; >>> - if (!IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID) || >>> - IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP)) >>> + if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP)) >>> + return; >>> + >>> + if (!IS_ENABLED(CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES) && >>> + !IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID)) >>> return; >>> /* >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index 0cdbbfbc5757..8c78b6a3d888 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -309,6 +309,11 @@ struct page *pfn_to_online_page(unsigned long pfn) >>> * Save some code text when online_section() + >>> * pfn_section_valid() are sufficient. >>> */ >>> + if (IS_ENABLED(CONFIG_HAVE_EARLY_SECTION_MEMMAP_HOLES)) { >>> + if (early_section(ms) && !memblock_is_memory(PFN_PHYS(pfn))) >>> + return NULL; >>> + } >>> + >>> if (IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID) && !pfn_valid(pfn)) >>> return NULL; >>> >> >> What about doing one step at a time and switching only over to generic >> pfn_valid() in case of CONFIG_SPARSEMEM? (meaning: freeing the memmap only >> with !CONFIG_SPARSEMEM) > > The "generic" pfn_valid() is only available with CONFIG_SPARSEMEM. > With FLATMEM it's wild west: > > $ git grep -w "define pfn_valid" arch/*/include/asm/ | wc -l > 22 > > This would actually mean that we still need arm64::pfn_valid() for the > FLATMEM case.
Right, which is the case on x86 etc. as well. (I was assuming that this patch was missing something)
> >> IOW, avoiding having to adjust generic pfn_valid()/pfn_to_online_page() at >> all. Am i missing something or should that be possible? > > We are back again to the question "should arm64 free its memmap". > If the answer is no, we don't need arm64::pfn_valid() for SPARSEMEM at all. > If the answer is yes, Anshuman's patch is way better than a custom > pfn_valid().
Well, I propose something in between: stop freeing with SPARSEMEM, continue freeing with FLATMEM.
-- Thanks,
David / dhildenb
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