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. 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.
