On Tue, May 25, 2021 at 11:30:15AM +0530, Anshuman Khandual wrote: > > 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. Ah, you are right, I missed this detail myself :) With CONFIG_SPARSEMEM_VMEMMAP as the only memory model for arm64, we can simply rid of arm64::pfn_valid() without any changes to the generic version. > > 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. > > -- Sincerely yours, Mike.
