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