Messages in this thread | | | Subject | Re: [PATCH v2 2/5] mm, page_poison: use static key more efficiently | From | David Hildenbrand <> | Date | Thu, 12 Nov 2020 17:06:38 +0100 |
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On 12.11.20 15:37, Vlastimil Babka wrote: > 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@suse.cz> > 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@suse.cz> > --- > 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; > >
LGTM.
-- Thanks,
David / dhildenb
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