On 4/21/21 5:54 PM, Mike Rapoport wrote: > On Wed, Apr 21, 2021 at 04:36:46PM +0530, Anshuman Khandual wrote: >> >> On 4/21/21 12:21 PM, Mike Rapoport wrote: >>> From: Mike Rapoport <rppt@xxxxxxxxxxxxx> >>> >>> The arm64's version of pfn_valid() differs from the generic because of two >>> reasons: >>> >>> * Parts of the memory map are freed during boot. This makes it necessary to >>> verify that there is actual physical memory that corresponds to a pfn >>> which is done by querying memblock. >>> >>> * There are NOMAP memory regions. These regions are not mapped in the >>> linear map and until the previous commit the struct pages representing >>> these areas had default values. >>> >>> As the consequence of absence of the special treatment of NOMAP regions in >>> the memory map it was necessary to use memblock_is_map_memory() in >>> pfn_valid() and to have pfn_valid_within() aliased to pfn_valid() so that >>> generic mm functionality would not treat a NOMAP page as a normal page. >>> >>> Since the NOMAP regions are now marked as PageReserved(), pfn walkers and >>> the rest of core mm will treat them as unusable memory and thus >>> pfn_valid_within() is no longer required at all and can be disabled by >>> removing CONFIG_HOLES_IN_ZONE on arm64. >> >> This makes sense. >> >>> >>> pfn_valid() can be slightly simplified by replacing >>> memblock_is_map_memory() with memblock_is_memory(). >>> >>> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> >>> --- >>> arch/arm64/Kconfig | 3 --- >>> arch/arm64/mm/init.c | 4 ++-- >>> 2 files changed, 2 insertions(+), 5 deletions(-) >>> >>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >>> index e4e1b6550115..58e439046d05 100644 >>> --- a/arch/arm64/Kconfig >>> +++ b/arch/arm64/Kconfig >>> @@ -1040,9 +1040,6 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK >>> def_bool y >>> depends on NUMA >>> >>> -config HOLES_IN_ZONE >>> - def_bool y >>> - >> >> Right. >> >>> source "kernel/Kconfig.hz" >>> >>> config ARCH_SPARSEMEM_ENABLE >>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c >>> index dc03bdc12c0f..eb3f56fb8c7c 100644 >>> --- a/arch/arm64/mm/init.c >>> +++ b/arch/arm64/mm/init.c >>> @@ -243,7 +243,7 @@ int pfn_valid(unsigned long pfn) >>> >>> /* >>> * ZONE_DEVICE memory does not have the memblock entries. >>> - * memblock_is_map_memory() check for ZONE_DEVICE based >>> + * 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 >>> @@ -254,7 +254,7 @@ int pfn_valid(unsigned long pfn) >>> return pfn_section_valid(ms, pfn); >>> } >>> #endif >>> - return memblock_is_map_memory(addr); >>> + return memblock_is_memory(addr); >> >> Wondering if MEMBLOCK_NOMAP is now being treated similarly to other >> memory pfns for page table walking purpose but with PageReserved(), >> why memblock_is_memory() is still required ? At this point, should >> not we just return valid for early_section() memory. As pfn_valid() >> now just implies that pfn has a struct page backing which has been >> already verified with valid_section() etc. > > memblock_is_memory() is required because arm64 frees unused parts of the > memory map. So, for instance, if we have 64M out of 128M populated in a > section the section based calculation would return 1 for a pfn in the > second half of the section, but there would be no memory map there. Understood.
