There is 8 byte page_ext->flags field allocated per page whenever
CONFIG_PAGE_EXTENSION is enabled. However, not every user of page_ext
uses flags. Therefore, check whether flags is needed at least by one
user and if so allocate space for it.
For example when page_table_check is enabled, on a machine with 128G
of memory before the fix:
[ 2.244288] allocated 536870912 bytes of page_ext
after the fix:
[ 2.160154] allocated 268435456 bytes of page_ext
Signed-off-by: Pasha Tatashin <[email protected]>
---
include/linux/page_ext.h | 7 +++++++
mm/page_ext.c | 12 +++++++++++-
mm/page_owner.c | 1 +
mm/page_table_check.c | 1 +
4 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index 22be4582faae..29909e135052 100644
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -12,10 +12,14 @@ struct page_ext_operations {
size_t size;
bool (*need)(void);
void (*init)(void);
+ bool using_shared_ext_flags;
};
#ifdef CONFIG_PAGE_EXTENSION
+/*
+ * The page_ext_flags users must set using_shared_ext_flags to true.
+ */
enum page_ext_flags {
PAGE_EXT_OWNER,
PAGE_EXT_OWNER_ALLOCATED,
@@ -31,6 +35,9 @@ enum page_ext_flags {
* page_ext helps us add more information about the page.
* All page_ext are allocated at boot or memory hotplug event,
* then the page_ext for pfn always exists.
+ * Note: that if none of the users of page_ext is setting
+ * using_shared_ext_flags to true, the field cannot be used,
+ * as it will be overlapped with another data.
*/
struct page_ext {
unsigned long flags;
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 4ee522fd381c..7443a797b96b 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -71,6 +71,7 @@ static bool need_page_idle(void)
}
static struct page_ext_operations page_idle_ops __initdata = {
.need = need_page_idle,
+ .using_shared_ext_flags = true,
};
#endif
@@ -86,7 +87,7 @@ static struct page_ext_operations *page_ext_ops[] __initdata = {
#endif
};
-unsigned long page_ext_size = sizeof(struct page_ext);
+unsigned long page_ext_size;
static unsigned long total_usage;
static struct page_ext *lookup_page_ext(const struct page *page);
@@ -105,6 +106,15 @@ static bool __init invoke_need_callbacks(void)
int entries = ARRAY_SIZE(page_ext_ops);
bool need = false;
+ for (i = 0; i < entries; i++) {
+ if (page_ext_ops[i]->need && page_ext_ops[i]->need()) {
+ if (page_ext_ops[i]->using_shared_ext_flags) {
+ page_ext_size = sizeof(struct page_ext);
+ break;
+ }
+ }
+ }
+
for (i = 0; i < entries; i++) {
if (page_ext_ops[i]->need && page_ext_ops[i]->need()) {
page_ext_ops[i]->offset = page_ext_size;
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 2d27f532df4c..612a988373cc 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -99,6 +99,7 @@ struct page_ext_operations page_owner_ops = {
.size = sizeof(struct page_owner),
.need = need_page_owner,
.init = init_page_owner,
+ .using_shared_flags = true,
};
static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index 93e633c1d587..74cfe89d5f53 100644
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -45,6 +45,7 @@ struct page_ext_operations page_table_check_ops = {
.size = sizeof(struct page_table_check),
.need = need_page_table_check,
.init = init_page_table_check,
+ .using_shared_ext_flags = false,
};
static struct page_table_check *get_page_table_check(struct page_ext *page_ext)
--
2.39.0.314.g84b9a713c41-goog
Hi Pasha,
I love your patch! Yet something to improve:
[auto build test ERROR on akpm-mm/mm-everything]
url: https://github.com/intel-lab-lkp/linux/commits/Pasha-Tatashin/mm-page_ext-Do-not-allocate-space-for-page_ext-flags-if-not-needed/20230112-055942
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20230111215906.2645056-1-pasha.tatashin%40soleen.com
patch subject: [PATCH] mm/page_ext: Do not allocate space for page_ext->flags if not needed
config: hexagon-randconfig-r012-20230110
compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project 8d9828ef5aa9688500657d36cd2aefbe12bbd162)
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/f195fe7b408dd821eef3d052e8ebd50cccb3df51
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Pasha-Tatashin/mm-page_ext-Do-not-allocate-space-for-page_ext-flags-if-not-needed/20230112-055942
git checkout f195fe7b408dd821eef3d052e8ebd50cccb3df51
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <[email protected]>
All errors (new ones prefixed by >>):
In file included from mm/page_owner.c:6:
In file included from include/linux/memblock.h:13:
In file included from arch/hexagon/include/asm/dma.h:9:
In file included from arch/hexagon/include/asm/io.h:334:
include/asm-generic/io.h:547:31: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
val = __raw_readb(PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:560:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
val = __le16_to_cpu((__le16 __force)__raw_readw(PCI_IOBASE + addr));
~~~~~~~~~~ ^
include/uapi/linux/byteorder/little_endian.h:37:51: note: expanded from macro '__le16_to_cpu'
#define __le16_to_cpu(x) ((__force __u16)(__le16)(x))
^
In file included from mm/page_owner.c:6:
In file included from include/linux/memblock.h:13:
In file included from arch/hexagon/include/asm/dma.h:9:
In file included from arch/hexagon/include/asm/io.h:334:
include/asm-generic/io.h:573:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
~~~~~~~~~~ ^
include/uapi/linux/byteorder/little_endian.h:35:51: note: expanded from macro '__le32_to_cpu'
#define __le32_to_cpu(x) ((__force __u32)(__le32)(x))
^
In file included from mm/page_owner.c:6:
In file included from include/linux/memblock.h:13:
In file included from arch/hexagon/include/asm/dma.h:9:
In file included from arch/hexagon/include/asm/io.h:334:
include/asm-generic/io.h:584:33: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
__raw_writeb(value, PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:594:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
__raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:604:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
__raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
~~~~~~~~~~ ^
>> mm/page_owner.c:102:3: error: field designator 'using_shared_flags' does not refer to any field in type 'struct page_ext_operations'; did you mean 'using_shared_ext_flags'?
.using_shared_flags = true,
^~~~~~~~~~~~~~~~~~
using_shared_ext_flags
include/linux/page_ext.h:15:7: note: 'using_shared_ext_flags' declared here
bool using_shared_ext_flags;
^
6 warnings and 1 error generated.
vim +102 mm/page_owner.c
97
98 struct page_ext_operations page_owner_ops = {
99 .size = sizeof(struct page_owner),
100 .need = need_page_owner,
101 .init = init_page_owner,
> 102 .using_shared_flags = true,
103 };
104
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests