prep_new_page() will always zero a new page (regardless of __GFP_ZERO) when
init_on_alloc is enabled, but will also always skip zeroing if the page was
already zeroed on free by init_on_free or page poisoning.
The latter check implemented by free_pages_prezeroed() can involve two
different static keys. As prep_new_page() is really a hot path, let's introduce
a single static key free_pages_not_prezeroed for this purpose and initialize it
in init_mem_debugging().
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
mm/page_alloc.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2a1be197649d..980780f5f242 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -171,6 +171,8 @@ EXPORT_SYMBOL(init_on_alloc);
DEFINE_STATIC_KEY_FALSE_RO(init_on_free);
EXPORT_SYMBOL(init_on_free);
+static DEFINE_STATIC_KEY_TRUE_RO(free_pages_not_prezeroed);
+
static bool _init_on_alloc_enabled_early __read_mostly
= IS_ENABLED(CONFIG_INIT_ON_ALLOC_DEFAULT_ON);
static int __init early_init_on_alloc(char *buf)
@@ -777,6 +779,16 @@ void init_mem_debugging()
}
}
+ /*
+ * We have a special static key that controls whether prep_new_page will
+ * never need to zero the page. This mode is enabled when page is
+ * already zeroed by init_on_free or page_poisoning zero mode.
+ */
+ if (_init_on_free_enabled_early ||
+ (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO)
+ && page_poisoning_enabled()))
+ static_branch_disable(&free_pages_not_prezeroed);
+
#ifdef CONFIG_PAGE_POISONING
/*
* Page poisoning is debug page alloc for some arches. If
@@ -2216,12 +2228,6 @@ static inline int check_new_page(struct page *page)
return 1;
}
-static inline bool free_pages_prezeroed(void)
-{
- return (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
- page_poisoning_enabled_static()) || want_init_on_free();
-}
-
#ifdef CONFIG_DEBUG_VM
/*
* With DEBUG_VM enabled, order-0 pages are checked for expected state when
@@ -2291,7 +2297,8 @@ static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags
{
post_alloc_hook(page, order, gfp_flags);
- if (!free_pages_prezeroed() && want_init_on_alloc(gfp_flags))
+ if (static_branch_likely(&free_pages_not_prezeroed)
+ && want_init_on_alloc(gfp_flags))
kernel_init_free_pages(page, 1 << order);
if (order && (gfp_flags & __GFP_COMP))
--
2.29.0
