[RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes
David Hildenbrand
david at redhat.com
Thu Apr 22 10:48:58 BST 2021
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 at arm.com>
>>> Cc: Will Deacon <will at kernel.org>
>>> Cc: Andrew Morton <akpm at linux-foundation.org>
>>> Cc: Mike Rapoport <rppt at kernel.org>
>>> Cc: David Hildenbrand <david at redhat.com>
>>> Cc: linux-arm-kernel at lists.infradead.org
>>> Cc: linux-kernel at vger.kernel.org
>>> Cc: linux-mm at kvack.org
>>> Suggested-by: David Hildenbrand <david at redhat.com>
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual at 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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