One easy way to shrink struct page is to simply remove the feature. The
patchset looked a bit complicated and does many other things.
Subject: slub: Remove struct page alignment restriction by dropping
cmpxchg_double on struct page fields
Remove the logic that will do cmpxchg_doubles on struct page fields with
the requirement of double word alignment. This allows struct page
to shrink by 8 bytes.
Signed-off-by: Christoph Lameter <c...@linux.com>
Index: linux/include/linux/mm_types.h
===================================================================
--- linux.orig/include/linux/mm_types.h 2014-01-14 13:55:00.611838185 -0600
+++ linux/include/linux/mm_types.h 2014-01-14 13:55:00.601838496 -0600
@@ -73,18 +73,12 @@ struct page {
};
union {
-#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
- defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
- /* Used for cmpxchg_double in slub */
- unsigned long counters;
-#else
/*
* Keep _count separate from slub cmpxchg_double data.
* As the rest of the double word is protected by
* slab_lock but _count is not.
*/
unsigned counters;
-#endif
struct {
@@ -195,15 +189,7 @@ struct page {
#ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
int _last_cpupid;
#endif
-}
-/*
- * 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.
- */
-#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE
- __aligned(2 * sizeof(unsigned long))
-#endif
-;
+};
struct page_frag {
struct page *page;
Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c 2014-01-14 13:55:00.611838185 -0600
+++ linux/mm/slub.c 2014-01-14 14:03:31.025903976 -0600
@@ -185,7 +185,6 @@ static inline bool kmem_cache_has_cpu_pa
/* Internal SLUB flags */
#define __OBJECT_POISON 0x80000000UL /* Poison object */
-#define __CMPXCHG_DOUBLE 0x40000000UL /* Use cmpxchg_double */
#ifdef CONFIG_SMP
static struct notifier_block slab_notifier;
@@ -362,34 +361,19 @@ static inline bool __cmpxchg_double_slab
const char *n)
{
VM_BUG_ON(!irqs_disabled());
-#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
- defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
- if (s->flags & __CMPXCHG_DOUBLE) {
- if (cmpxchg_double(&page->freelist, &page->counters,
- freelist_old, counters_old,
- freelist_new, counters_new))
- return 1;
- } else
-#endif
- {
- slab_lock(page);
- if (page->freelist == freelist_old &&
- page->counters == counters_old) {
- page->freelist = freelist_new;
- page->counters = counters_new;
- slab_unlock(page);
- return 1;
- }
+
+ slab_lock(page);
+ if (page->freelist == freelist_old &&
+ page->counters == counters_old) {
+ page->freelist = freelist_new;
+ page->counters = counters_new;
slab_unlock(page);
+ return 1;
}
-
- cpu_relax();
stat(s, CMPXCHG_DOUBLE_FAIL);
-
#ifdef SLUB_DEBUG_CMPXCHG
printk(KERN_INFO "%s %s: cmpxchg double redo ", n, s->name);
#endif
-
return 0;
}
@@ -398,40 +382,14 @@ static inline bool cmpxchg_double_slab(s
void *freelist_new, unsigned long counters_new,
const char *n)
{
-#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
- defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
- if (s->flags & __CMPXCHG_DOUBLE) {
- if (cmpxchg_double(&page->freelist, &page->counters,
- freelist_old, counters_old,
- freelist_new, counters_new))
- return 1;
- } else
-#endif
- {
- unsigned long flags;
-
- local_irq_save(flags);
- slab_lock(page);
- if (page->freelist == freelist_old &&
- page->counters == counters_old) {
- page->freelist = freelist_new;
- page->counters = counters_new;
- slab_unlock(page);
- local_irq_restore(flags);
- return 1;
- }
- slab_unlock(page);
- local_irq_restore(flags);
- }
-
- cpu_relax();
- stat(s, CMPXCHG_DOUBLE_FAIL);
-
-#ifdef SLUB_DEBUG_CMPXCHG
- printk(KERN_INFO "%s %s: cmpxchg double redo ", n, s->name);
-#endif
+ unsigned long flags;
+ int r;
- return 0;
+ local_irq_save(flags);
+ r = __cmpxchg_double_slab(s, page, freelist_old, counters_old,
+ freelist_new, counters_new, n);
+ local_irq_restore(flags);
+ return r;
}
#ifdef CONFIG_SLUB_DEBUG
@@ -3078,13 +3036,6 @@ static int kmem_cache_open(struct kmem_c
}
}
-#if defined(CONFIG_HAVE_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;
-#endif
-
/*
* The larger the object size is, the more pages we want on the partial
* list to avoid pounding the page allocator excessively.
@@ -4608,10 +4559,8 @@ static ssize_t sanity_checks_store(struc
const char *buf, size_t length)
{
s->flags &= ~SLAB_DEBUG_FREE;
- if (buf[0] == '1') {
- s->flags &= ~__CMPXCHG_DOUBLE;
+ if (buf[0] == '1')
s->flags |= SLAB_DEBUG_FREE;
- }
return length;
}
SLAB_ATTR(sanity_checks);
@@ -4625,10 +4574,8 @@ static ssize_t trace_store(struct kmem_c
size_t length)
{
s->flags &= ~SLAB_TRACE;
- if (buf[0] == '1') {
- s->flags &= ~__CMPXCHG_DOUBLE;
+ if (buf[0] == '1')
s->flags |= SLAB_TRACE;
- }
return length;
}
SLAB_ATTR(trace);
@@ -4645,10 +4592,8 @@ static ssize_t red_zone_store(struct kme
return -EBUSY;
s->flags &= ~SLAB_RED_ZONE;
- if (buf[0] == '1') {
- s->flags &= ~__CMPXCHG_DOUBLE;
+ if (buf[0] == '1')
s->flags |= SLAB_RED_ZONE;
- }
calculate_sizes(s, -1);
return length;
}
@@ -4666,10 +4611,8 @@ static ssize_t poison_store(struct kmem_
return -EBUSY;
s->flags &= ~SLAB_POISON;
- if (buf[0] == '1') {
- s->flags &= ~__CMPXCHG_DOUBLE;
+ if (buf[0] == '1')
s->flags |= SLAB_POISON;
- }
calculate_sizes(s, -1);
return length;
}
@@ -4687,10 +4630,9 @@ static ssize_t store_user_store(struct k
return -EBUSY;
s->flags &= ~SLAB_STORE_USER;
- if (buf[0] == '1') {
- s->flags &= ~__CMPXCHG_DOUBLE;
+ if (buf[0] == '1')
s->flags |= SLAB_STORE_USER;
- }
+
calculate_sizes(s, -1);
return length;
}
Index: linux/arch/Kconfig
===================================================================
--- linux.orig/arch/Kconfig 2014-01-14 13:55:00.611838185 -0600
+++ linux/arch/Kconfig 2014-01-14 13:55:00.601838496 -0600
@@ -289,14 +289,6 @@ 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.
-
config HAVE_CMPXCHG_LOCAL
bool
Index: linux/arch/s390/Kconfig
===================================================================
--- linux.orig/arch/s390/Kconfig 2014-01-14 13:55:00.611838185 -0600
+++ linux/arch/s390/Kconfig 2014-01-14 13:55:00.601838496 -0600
@@ -102,7 +102,6 @@ config S390
select GENERIC_FIND_FIRST_BIT
select GENERIC_SMP_IDLE_THREAD
select GENERIC_TIME_VSYSCALL
- select HAVE_ALIGNED_STRUCT_PAGE if SLUB
select HAVE_ARCH_JUMP_LABEL if !MARCH_G5
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK
Index: linux/arch/x86/Kconfig
===================================================================
--- linux.orig/arch/x86/Kconfig 2014-01-14 13:55:00.611838185 -0600
+++ linux/arch/x86/Kconfig 2014-01-14 13:55:00.601838496 -0600
@@ -77,7 +77,6 @@ config X86
select HAVE_PERF_USER_STACK_DUMP
select HAVE_DEBUG_KMEMLEAK
select ANON_INODES
- select HAVE_ALIGNED_STRUCT_PAGE if SLUB
select HAVE_CMPXCHG_LOCAL
select HAVE_CMPXCHG_DOUBLE
select HAVE_ARCH_KMEMCHECK
--
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