The patch titled
Subject: mm/page_ext: do not allocate space for page_ext->flags if not needed
has been added to the -mm mm-unstable branch. Its filename is
mm-page_ext-do-not-allocate-space-for-page_ext-flags-if-not-needed.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_ext-do-not-allocate-space-for-page_ext-flags-if-not-needed.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Subject: mm/page_ext: do not allocate space for page_ext->flags if not needed
Date: Fri, 13 Jan 2023 15:42:53 +0000
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
Also, add a comment before page_ext_operations that describes the
field, and remove check if need() is set, as that is now a required
field.
Link: https://lkml.kernel.org/r/20230113154253.92480-1-pasha.tatashin@xxxxxxxxxx
Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Li Zhe <lizhe.67@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/include/linux/page_ext.h~mm-page_ext-do-not-allocate-space-for-page_ext-flags-if-not-needed
+++ a/include/linux/page_ext.h
@@ -7,15 +7,31 @@
#include <linux/stackdepot.h>
struct pglist_data;
+
+/*
+ * Each Page Extension client must define page_ext_operations in
+ * page_ext_ops array.
+ * offset offset to the client's data within page_ext. Offset is returned to
+ * the client by page_ext_init.
+ * size the size of the client data within page_ext.
+ * need() function that returns true if client requires page_ext
+ * init() (optional) called to initialize client once page_exts are allocated.
+ * using_shared_ext_flags true when client is using shared page_ext->flags
+ * field.
+ */
struct page_ext_operations {
size_t offset;
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 +47,9 @@ 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;
--- a/mm/page_ext.c~mm-page_ext-do-not-allocate-space-for-page_ext-flags-if-not-needed
+++ a/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_
#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);
@@ -106,7 +107,16 @@ static bool __init invoke_need_callbacks
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]->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]->offset = page_ext_size;
page_ext_size += page_ext_ops[i]->size;
need = true;
--- a/mm/page_owner.c~mm-page_ext-do-not-allocate-space-for-page_ext-flags-if-not-needed
+++ a/mm/page_owner.c
@@ -99,6 +99,7 @@ struct page_ext_operations page_owner_op
.size = sizeof(struct page_owner),
.need = need_page_owner,
.init = init_page_owner,
+ .using_shared_ext_flags = true,
};
static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
--- a/mm/page_table_check.c~mm-page_ext-do-not-allocate-space-for-page_ext-flags-if-not-needed
+++ a/mm/page_table_check.c
@@ -45,6 +45,7 @@ struct page_ext_operations page_table_ch
.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)
_
Patches currently in -mm which might be from pasha.tatashin@xxxxxxxxxx are
mm-page_ext-do-not-allocate-space-for-page_ext-flags-if-not-needed.patch
