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mm,slub,x86: decouple size of struct page from CONFIG_CMPXCHG_LOCAL

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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 <heiko.carstens@de.ibm.com>
Acked-by: Christoph 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Heiko Carstens 2012-01-12 17:17:27 -08:00 committed by Linus Torvalds
parent 0d259cf819
commit 43570fd2f4
4 changed files with 16 additions and 8 deletions
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8
arch/Kconfig
View File

@ -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"

1
arch/x86/Kconfig
View File

@ -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

9
include/linux/mm_types.h
View File

@ -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
;

6
mm/slub.c
View File

@ -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;