Re: [PATCH v2 2/5] mm, page_poison: use static key more efficiently
From: Vlastimil Babka
Date: Thu Nov 12 2020 - 09:38:09 EST
On 11/11/20 4:38 PM, David Hildenbrand wrote:
On 03.11.20 16:22, Vlastimil Babka wrote:
Commit 11c9c7edae06 ("mm/page_poison.c: replace bool variable with static key")
changed page_poisoning_enabled() to a static key check. However, the function
is not inlined, so each check still involves a function call with overhead not
eliminated when page poisoning is disabled.
Analogically to how debug_pagealloc is handled, this patch converts
page_poisoning_enabled() back to boolean check, and introduces
page_poisoning_enabled_static() for fast paths. Both functions are inlined.
The function kernel_poison_pages() is also called unconditionally and does
the static key check inside. Remove it from there and put it to callers. Also
split it to two functions kernel_poison_pages() and kernel_unpoison_pages()
instead of the confusing bool parameter.
Also optimize the check that enables page poisoning instead of debug_pagealloc
for architectures without proper debug_pagealloc support. Move the check to
init_mem_debugging_and_hardening() to enable a single static key instead of
having two static branches in page_poisoning_enabled_static().
[...]
+ * For use in fast paths after init_mem_debugging() has run, or when a
+ * false negative result is not harmful when called too early.
+ */
+static inline bool page_poisoning_enabled_static(void)
+{
+ return (static_branch_unlikely(&_page_poisoning_enabled));
As already mentioned IIRC:
Yes, it was, and I thought I fixed it. Guess not.
return static_branch_unlikely(&_page_poisoning_enabled);
+}
@@ -1260,7 +1271,8 @@ static __always_inline bool free_pages_prepare(struct page *page,
if (want_init_on_free())
kernel_init_free_pages(page, 1 << order);
- kernel_poison_pages(page, 1 << order, 0);
+ if (page_poisoning_enabled_static())
+ kernel_poison_pages(page, 1 << order);
This would look much better by having kernel_poison_pages() simply be
implemented in a header, where the static check is performed.
Take a look at how it's handled in mm/shuffle.h
Ok. Fixup below.
----8<----
From 7ce26ba61296f583f0f9089e7887f07424f25d2c Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@xxxxxxx>
Date: Thu, 12 Nov 2020 15:20:58 +0100
Subject: [PATCH] mm, page_poison: use static key more efficiently-fix
Non-functional cleanups, per David Hildenbrand.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
include/linux/mm.h | 16 +++++++++++++---
mm/page_alloc.c | 7 +++----
mm/page_poison.c | 4 ++--
3 files changed, 18 insertions(+), 9 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4d6dd9f44571..861b9392b5dc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2867,8 +2867,8 @@ extern int apply_to_existing_page_range(struct mm_struct *mm,
extern void init_mem_debugging_and_hardening(void);
#ifdef CONFIG_PAGE_POISONING
-extern void kernel_poison_pages(struct page *page, int numpages);
-extern void kernel_unpoison_pages(struct page *page, int numpages);
+extern void __kernel_poison_pages(struct page *page, int numpages);
+extern void __kernel_unpoison_pages(struct page *page, int numpages);
extern bool _page_poisoning_enabled_early;
DECLARE_STATIC_KEY_FALSE(_page_poisoning_enabled);
static inline bool page_poisoning_enabled(void)
@@ -2881,7 +2881,17 @@ static inline bool page_poisoning_enabled(void)
*/
static inline bool page_poisoning_enabled_static(void)
{
- return (static_branch_unlikely(&_page_poisoning_enabled));
+ return static_branch_unlikely(&_page_poisoning_enabled);
+}
+static inline void kernel_poison_pages(struct page *page, int numpages)
+{
+ if (page_poisoning_enabled_static())
+ __kernel_poison_pages(page, numpages);
+}
+static inline void kernel_unpoison_pages(struct page *page, int numpages)
+{
+ if (page_poisoning_enabled_static())
+ __kernel_unpoison_pages(page, numpages);
}
#else
static inline bool page_poisoning_enabled(void) { return false; }
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fd7f9345adc0..1388b5939551 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1271,8 +1271,8 @@ static __always_inline bool free_pages_prepare(struct page *page,
if (want_init_on_free())
kernel_init_free_pages(page, 1 << order);
- if (page_poisoning_enabled_static())
- kernel_poison_pages(page, 1 << order);
+ kernel_poison_pages(page, 1 << order);
+
/*
* arch_free_page() can make the page's contents inaccessible. s390
* does this. So nothing which can access the page's contents should
@@ -2281,8 +2281,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
if (debug_pagealloc_enabled_static())
kernel_map_pages(page, 1 << order, 1);
kasan_alloc_pages(page, order);
- if (page_poisoning_enabled_static())
- kernel_unpoison_pages(page, 1 << order);
+ kernel_unpoison_pages(page, 1 << order);
set_page_owner(page, order, gfp_flags);
}
diff --git a/mm/page_poison.c b/mm/page_poison.c
index dd7aeada036f..4d75fc9ccc7a 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -30,7 +30,7 @@ static void poison_page(struct page *page)
kunmap_atomic(addr);
}
-void kernel_poison_pages(struct page *page, int n)
+void __kernel_poison_pages(struct page *page, int n)
{
int i;
@@ -89,7 +89,7 @@ static void unpoison_page(struct page *page)
kunmap_atomic(addr);
}
-void kernel_unpoison_pages(struct page *page, int n)
+void __kernel_unpoison_pages(struct page *page, int n)
{
int i;
--
2.29.1