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SubjectRe: [PATCH] mm: Warn once when a page is freed with PG_mlocked set V2
Date
> From eee677ddea61b1331a3bd8e402a0d02437fe872a Mon Sep 17 00:00:00 2001
> From: Johannes Weiner <hannes@cmpxchg.org>
> Date: Wed, 15 Jul 2009 23:40:28 +0200
> Subject: [patch] mm: non-atomic test-clear of PG_mlocked on free
>
> By the time PG_mlocked is cleared in the page freeing path, nobody
> else is looking at our page->flags anymore.
>
> It is thus safe to make the test-and-clear non-atomic and thereby
> removing an unnecessary and expensive operation from a hotpath.

I like this patch. but can you please separate two following patches?
- introduce __TESTCLEARFLAG()
- non-atomic test-clear of PG_mlocked on free



>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
> include/linux/page-flags.h | 12 +++++++++---
> mm/page_alloc.c | 4 ++--
> 2 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index e2e5ce5..10e6011 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -158,6 +158,9 @@ static inline int TestSetPage##uname(struct page *page) \
> static inline int TestClearPage##uname(struct page *page) \
> { return test_and_clear_bit(PG_##lname, &page->flags); }
>
> +#define __TESTCLEARFLAG(uname, lname) \
> +static inline int __TestClearPage##uname(struct page *page) \
> + { return __test_and_clear_bit(PG_##lname, &page->flags); }
>
> #define PAGEFLAG(uname, lname) TESTPAGEFLAG(uname, lname) \
> SETPAGEFLAG(uname, lname) CLEARPAGEFLAG(uname, lname)
> @@ -184,6 +187,9 @@ static inline void __ClearPage##uname(struct page *page) { }
> #define TESTCLEARFLAG_FALSE(uname) \
> static inline int TestClearPage##uname(struct page *page) { return 0; }
>
> +#define __TESTCLEARFLAG_FALSE(uname) \
> +static inline int __TestClearPage##uname(struct page *page) { return 0; }
> +
> struct page; /* forward declaration */
>
> TESTPAGEFLAG(Locked, locked) TESTSETFLAG(Locked, locked)
> @@ -250,11 +256,11 @@ PAGEFLAG(Unevictable, unevictable) __CLEARPAGEFLAG(Unevictable, unevictable)
> #ifdef CONFIG_HAVE_MLOCKED_PAGE_BIT
> #define MLOCK_PAGES 1
> PAGEFLAG(Mlocked, mlocked) __CLEARPAGEFLAG(Mlocked, mlocked)
> - TESTSCFLAG(Mlocked, mlocked)
> + TESTSCFLAG(Mlocked, mlocked) __TESTCLEARFLAG(Mlocked, mlocked)
> #else
> #define MLOCK_PAGES 0
> -PAGEFLAG_FALSE(Mlocked)
> - SETPAGEFLAG_NOOP(Mlocked) TESTCLEARFLAG_FALSE(Mlocked)
> +PAGEFLAG_FALSE(Mlocked) SETPAGEFLAG_NOOP(Mlocked)
> + TESTCLEARFLAG_FALSE(Mlocked) __TESTCLEARFLAG_FALSE(Mlocked)
> #endif
>
> #ifdef CONFIG_IA64_UNCACHED_ALLOCATOR
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index caa9268..b0c8758 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -557,7 +557,7 @@ static void __free_pages_ok(struct page *page, unsigned int order)
> unsigned long flags;
> int i;
> int bad = 0;
> - int wasMlocked = TestClearPageMlocked(page);
> + int wasMlocked = __TestClearPageMlocked(page);
>
> kmemcheck_free_shadow(page, order);
>
> @@ -1021,7 +1021,7 @@ static void free_hot_cold_page(struct page *page, int cold)
> struct zone *zone = page_zone(page);
> struct per_cpu_pages *pcp;
> unsigned long flags;
> - int wasMlocked = TestClearPageMlocked(page);
> + int wasMlocked = __TestClearPageMlocked(page);
>
> kmemcheck_free_shadow(page, 0);
>
> --
> 1.6.3
>
> --
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