On 4/21/21 5:54 PM, Mike Rapoport wrote:

On Wed, Apr 21, 2021 at 04:36:46PM +0530, Anshuman Khandual wrote:

quoted

On 4/21/21 12:21 PM, Mike Rapoport wrote:

quoted

From: Mike Rapoport <redacted>

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.

quoted

pfn_valid() can be slightly simplified by replacing
memblock_is_map_memory() with memblock_is_memory().

Signed-off-by: Mike Rapoport <redacted>
---
 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.

quoted

 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.

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