diff mbox series

[v2] mm/page_ext: Do not allocate space for page_ext->flags if not needed

Message ID 20230112153348.3202173-1-pasha.tatashin@soleen.com
State New
Headers
Series [v2] mm/page_ext: Do not allocate space for page_ext->flags if not needed |

Commit Message

Pasha Tatashin Jan. 12, 2023, 3:33 p.m. UTC 
  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 <pasha.tatashin@soleen.com>
---
 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(-)

Changelog:
v2: Fixed field name in page_owner.c that caused build error.

Comments

Andrew Morton Jan. 12, 2023, 9:29 p.m. UTC | #1 
On Thu, 12 Jan 2023 15:33:48 +0000 Pasha Tatashin <pasha.tatashin@soleen.com> wrote:

> 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
> 

Looks nice.

Does it work correctly with early_page_ext=1?

> --- 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;
>  };

Seems overly complicated.  Can we change the three early-init
functions such as setup_early_page_ext() to simply set some global bool
flag?

>  #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()) {

I don't think this (or the below) need to check for ->need==NULL?

> +			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;
Pasha Tatashin Jan. 13, 2023, 2:44 p.m. UTC | #2 
On Thu, Jan 12, 2023 at 4:29 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 12 Jan 2023 15:33:48 +0000 Pasha Tatashin <pasha.tatashin@soleen.com> wrote:
>
> > 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
> >
>
> Looks nice.

Hi Andrew,

Thanks for looking at this patch.

>
> Does it work correctly with early_page_ext=1?

Yes, early_page_ext=1 moves page_ext_init() earlier, and disables
deferred page initialization, but that is not an issue for the changes
in this patch.

>
> > --- 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;
> >  };
>
> Seems overly complicated.  Can we change the three early-init
> functions such as setup_early_page_ext() to simply set some global bool
> flag?

We can't because , in the following loop:

       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;

page_ext_size must already either include or not the space for the
shared flag field.

>
> >  #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()) {
>
> I don't think this (or the below) need to check for ->need==NULL?

Good point, I will remove the check, and also update the comment that
the "need" function must be defined for every item in the page_ext_ops
array.

Thanks,
Pasha
diff mbox series

Patch

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..1a62ab3fc00e 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_ext_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)