Re: [RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes

From: Mike Rapoport
Date: Thu Apr 22 2021 - 04:27:32 EST

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On Thu, Apr 22, 2021 at 01:20:23PM +0530, 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;

Nit: we already did

addr = PFN_PHYS(pfn);

a few lines above :)

> +
> + 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);

Please make it inside #ifdef CONFIG_ARCH_MEMBLOCK

> 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;

Can you please add a comment that says that architecture should provide a
way to detect holes in the memory map to be able to free its part?

> /*
> 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;
>
> --
> 2.20.1
>

--
Sincerely yours,
Mike.

Next message: HORIGUCHI NAOYA(堀口　直也): "Re: [PATCH] mm: hugetlb: fix a race between memory-failure/soft_offline and gather_surplus_pages"
Previous message: Greg KH: "Re: [PATCH] SUNRPC: Add a check for gss_release_msg"
In reply to: Anshuman Khandual: "[RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes"
Next in thread: Anshuman Khandual: "Re: [RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes"
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