From 43570fd2f47ba518145e9289f54cde3dba4c8b25 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Thu, 12 Jan 2012 17:17:27 -0800 Subject: [PATCH] mm,slub,x86: decouple size of struct page from CONFIG_CMPXCHG_LOCAL While implementing cmpxchg_double() on s390 I realized that we don't set CONFIG_CMPXCHG_LOCAL despite the fact that we have support for it. However setting that option will increase the size of struct page by eight bytes on 64 bit, which we certainly do not want. Also, it doesn't make sense that a present cpu feature should increase the size of struct page. Besides that it looks like the dependency to CMPXCHG_LOCAL is wrong and that it should depend on CMPXCHG_DOUBLE instead. This patch: If an architecture supports CMPXCHG_LOCAL this shouldn't result automatically in larger struct pages if the SLUB allocator is used. Instead introduce a new config option "HAVE_ALIGNED_STRUCT_PAGE" which can be selected if a double word aligned struct page is required. Also update x86 Kconfig so that it should work as before. Signed-off-by: Heiko Carstens Acked-by: Christoph Lameter Cc: Pekka Enberg Cc: Ingo Molnar Cc: Thomas Gleixner Cc: "H. Peter Anvin" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/Kconfig | 8 ++++++++ arch/x86/Kconfig | 1 + include/linux/mm_types.h | 9 ++++----- mm/slub.c | 6 +++--- 4 files changed, 16 insertions(+), 8 deletions(-) diff --git a/arch/Kconfig b/arch/Kconfig index 2505740..a2c5c07 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -185,4 +185,12 @@ config HAVE_RCU_TABLE_FREE config ARCH_HAVE_NMI_SAFE_CMPXCHG bool +config HAVE_ALIGNED_STRUCT_PAGE + bool + help + This makes sure that struct pages are double word aligned and that + e.g. the SLUB allocator can perform double word atomic operations + on a struct page for better performance. However selecting this + might increase the size of a struct page by a word. + source "kernel/gcov/Kconfig" diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index a150f4c..5201a2c 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -60,6 +60,7 @@ config X86 select PERF_EVENTS select HAVE_PERF_EVENTS_NMI select ANON_INODES + select HAVE_ALIGNED_STRUCT_PAGE if SLUB && !M386 select HAVE_ARCH_KMEMCHECK select HAVE_USER_RETURN_NOTIFIER select ARCH_BINFMT_ELF_RANDOMIZE_PIE diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 5b42f1b..3cc3062 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -151,12 +151,11 @@ struct page { #endif } /* - * If another subsystem starts using the double word pairing for atomic - * operations on struct page then it must change the #if to ensure - * proper alignment of the page struct. + * The struct page can be forced to be double word aligned so that atomic ops + * on double words work. The SLUB allocator can make use of such a feature. */ -#if defined(CONFIG_SLUB) && defined(CONFIG_CMPXCHG_LOCAL) - __attribute__((__aligned__(2*sizeof(unsigned long)))) +#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE + __aligned(2 * sizeof(unsigned long)) #endif ; diff --git a/mm/slub.c b/mm/slub.c index 5d37b5e4..72aa841 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -366,7 +366,7 @@ static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct page *page const char *n) { VM_BUG_ON(!irqs_disabled()); -#ifdef CONFIG_CMPXCHG_DOUBLE +#if defined(CONFIG_CMPXCHG_DOUBLE) && defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) if (s->flags & __CMPXCHG_DOUBLE) { if (cmpxchg_double(&page->freelist, &page->counters, freelist_old, counters_old, @@ -400,7 +400,7 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page, void *freelist_new, unsigned long counters_new, const char *n) { -#ifdef CONFIG_CMPXCHG_DOUBLE +#if defined(CONFIG_CMPXCHG_DOUBLE) && defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) if (s->flags & __CMPXCHG_DOUBLE) { if (cmpxchg_double(&page->freelist, &page->counters, freelist_old, counters_old, @@ -3014,7 +3014,7 @@ static int kmem_cache_open(struct kmem_cache *s, } } -#ifdef CONFIG_CMPXCHG_DOUBLE +#if defined(CONFIG_CMPXCHG_DOUBLE) && defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) if (system_has_cmpxchg_double() && (s->flags & SLAB_DEBUG_FLAGS) == 0) /* Enable fast mode */ s->flags |= __CMPXCHG_DOUBLE; -- 2.7.4