On 5/24/21 12:22 PM, Mike Rapoport wrote: > Hello Anshuman, > > On Mon, May 24, 2021 at 10:28:32AM +0530, Anshuman Khandual wrote: >> >> On 4/22/21 1:20 PM, 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@xxxxxxx> >>> Cc: Will Deacon <will@xxxxxxxxxx> >>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >>> Cc: Mike Rapoport <rppt@xxxxxxxxxx> >>> Cc: David Hildenbrand <david@xxxxxxxxxx> >>> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx >>> Cc: linux-kernel@xxxxxxxxxxxxxxx >>> Cc: linux-mm@xxxxxxxxx >>> Suggested-by: David Hildenbrand <david@xxxxxxxxxx> >>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> >>> --- >>> 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@xxxxxxxxxx/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@xxxxxxx/ >>> >>> 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 >> >> Hello David/Mike, >> >> Now that pfn_is_map_memory() usage has been decoupled from pfn_valid() and >> SPARSEMEM_VMEMMAP is only available memory model on arm64, wondering if we >> still need this HAVE_EARLY_SECTION_MEMMAP_HOLES proposal ? Please do kindly >> suggest. Thank you. > > Even now arm64 still frees parts of the memory map and pfn_valid() should > be able to tell if a part of a section is freed or not. > > For instance for the following memory configuration > > |<----section---->|<----hole---->|<----section---->| > +--------+--------+--------------+--------+--------+ > | bank 0 | unused | | bank 1 | unused | > +--------+--------+--------------+--------+--------+ > > the memory map corresponding to the "unused" areas is freed, but the generic > pfn_valid() will still return 1 there. But is not free_unused_memmap() return early when CONFIG_SPARSEMEM_VMEMMAP is enabled, which is the only option now on arm64. Then how can memmap have holes (from unused areas) anymore ? Am I missing something here. > > So we either should stop freeing unused memory map on arm64, or keep > arm64::pfn_valid() or implement something along the lines of this patch. > > I personally don't think that the memory savings from freeing the unused > memory map worth the pain of maintenance and bugs happening here and there. >
