Re: [RFC V2] mm: Enable generic pfn_valid() to handle early sections with memmap holes
From: David Hildenbrand
Date: Thu Apr 22 2021 - 05:49:07 EST
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@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
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