Commit 43570fd2 authored by Heiko Carstens's avatar Heiko Carstens Committed by Linus Torvalds
Browse files

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: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: default avatarChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0d259cf8

arch/Kconfig

+8 −0
Original line number Diff line number Diff line
@@ -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"

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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

include/linux/mm_types.h

+4 −5
Original line number Diff line number Diff line
@@ -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

;

mm/slub.c

+3 −3
Original line number Diff line number Diff line
@@ -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;

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