Re: [RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes
From: David Hildenbrand
Date: Tue May 25 2021 - 06:04:50 EST
On 25.05.21 12:03, Mike Rapoport wrote:
On Tue, May 25, 2021 at 03:22:53PM +0530, Anshuman Khandual wrote:
On 5/25/21 12:02 PM, Mike Rapoport wrote:
On Tue, May 25, 2021 at 11:30:15AM +0530, Anshuman Khandual wrote:
On 5/24/21 12:22 PM, Mike Rapoport wrote:
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.
But is not free_unused_memmap() return early when CONFIG_SPARSEMEM_VMEMMAP
is enabled, which is the only option now on arm64. Then how can memmap have
holes (from unused areas) anymore ? Am I missing something here.
Ah, you are right, I missed this detail myself :)
With CONFIG_SPARSEMEM_VMEMMAP as the only memory model for arm64, we can
simply rid of arm64::pfn_valid() without any changes to the generic
version.
Though just moved the pfn bits sanity check into generic pfn_valid().
I hope this looks okay.
From 7a63f460bcb6ae171c2081bfad81edd9e8f3b7a0 Mon Sep 17 00:00:00 2001
From: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Date: Tue, 25 May 2021 10:27:09 +0100
Subject: [PATCH] arm64/mm: Drop HAVE_ARCH_PFN_VALID
CONFIG_SPARSEMEM_VMEMMAP is now the only available memory model on arm64
platforms and free_unused_memmap() would just return without creating any
holes in the memmap mapping. There is no need for any special handling in
pfn_valid() and HAVE_ARCH_PFN_VALID can just be dropped. This also moves
the pfn upper bits sanity check into generic pfn_valid().
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Indeed, looks good
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
---
arch/arm64/Kconfig | 1 -
arch/arm64/include/asm/page.h | 1 -
arch/arm64/mm/init.c | 37 -----------------------------------
include/linux/mmzone.h | 9 +++++++++
4 files changed, 9 insertions(+), 39 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index d7dc8698cf8e..7904728befcc 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -154,7 +154,6 @@ 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_RANDOMIZE_KSTACK_OFFSET
select HAVE_ARCH_SECCOMP_FILTER
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 725aa84f2faa..49019ea0c8a8 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -219,43 +219,6 @@ 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);
- 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 = __pfn_to_section(pfn);
- if (!valid_section(ms))
- return 0;
-
- /*
- * ZONE_DEVICE memory does not have the memblock entries.
- * memblock_is_map_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);
-
- 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 a9b263d4cf9d..d0c4fc506fa3 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1443,6 +1443,15 @@ static inline int pfn_valid(unsigned long 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(PFN_PHYS(pfn)) != pfn)
+ return 0;
+
if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
return 0;
ms = __nr_to_section(pfn_to_section_nr(pfn));
--
2.20.1
--
Thanks,
David / dhildenb