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SubjectRe: [slubllv6 06/17] slub: Add cmpxchg_double_slab()
On Thu, 26 May 2011, David Rientjes wrote:

> > +static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
> > + void *freelist_old, unsigned long counters_old,
> > + void *freelist_new, unsigned long counters_new,
> > + const char *n)
>
> This is defined only under CONFIG_SLUB_DEBUG, which is surely a mistake:
>
> mm/slub.c: In function ‘acquire_slab’:
> mm/slub.c:1460: error: implicit declaration of function ‘cmpxchg_double_slab’

Ok.

> > +#ifdef CONFIG_CMPXCHG_DOUBLE
> > + if (system_has_cmpxchg_double() && (s->flags & SLAB_DEBUG_FLAGS) == 0)
> > + /* Enable fast mode */
> > + s->flags |= __CMPXCHG_DOUBLE;
> > +#endif
> > +
>
> Not sure why this is excluded for SLAB_DEBUG_FLAGS? If it really should
> be, then we should clear __CMPXCHG_DOUBLE if debugging features are
> enabled through sysfs as well.

Right. Fixed up patch follows:



Subject: slub: Add cmpxchg_double_slab()

Add a function that operates on the second doubleword in the page struct
and manipulates the object counters, the freelist and the frozen attribute.

Signed-off-by: Christoph Lameter <cl@linux.com>

---
include/linux/slub_def.h | 1
mm/slub.c | 65 +++++++++++++++++++++++++++++++++++++++++++----
2 files changed, 61 insertions(+), 5 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2011-05-31 11:57:59.622937422 -0500
+++ linux-2.6/mm/slub.c 2011-05-31 12:03:16.652935392 -0500
@@ -131,6 +131,9 @@ static inline int kmem_cache_debug(struc
/* Enable to test recovery from slab corruption on boot */
#undef SLUB_RESILIENCY_TEST

+/* Enable to log cmpxchg failures */
+#undef SLUB_DEBUG_CMPXCHG
+
/*
* Mininum number of partial slabs. These will be left on the partial
* lists even if they are empty. kmem_cache_shrink may reclaim them.
@@ -170,6 +173,7 @@ static inline int kmem_cache_debug(struc

/* Internal SLUB flags */
#define __OBJECT_POISON 0x80000000UL /* Poison object */
+#define __CMPXCHG_DOUBLE 0x40000000UL /* Use cmpxchg_double */

static int kmem_size = sizeof(struct kmem_cache);

@@ -338,6 +342,37 @@ static inline int oo_objects(struct kmem
return x.x & OO_MASK;
}

+static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
+ void *freelist_old, unsigned long counters_old,
+ void *freelist_new, unsigned long counters_new,
+ const char *n)
+{
+#ifdef CONFIG_CMPXCHG_DOUBLE
+ if (s->flags & __CMPXCHG_DOUBLE) {
+ if (cmpxchg_double(&page->freelist,
+ freelist_old, counters_old,
+ freelist_new, counters_new))
+ return 1;
+ } else
+#endif
+ {
+ if (page->freelist == freelist_old && page->counters == counters_old) {
+ page->freelist = freelist_new;
+ page->counters = counters_new;
+ 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;
+}
+
#ifdef CONFIG_SLUB_DEBUG
/*
* Determine a map of object in use on a page.
@@ -2600,6 +2635,12 @@ static int kmem_cache_open(struct kmem_c
}
}

+#ifdef CONFIG_CMPXCHG_DOUBLE
+ 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.
@@ -4252,8 +4293,10 @@ static ssize_t sanity_checks_store(struc
const char *buf, size_t length)
{
s->flags &= ~SLAB_DEBUG_FREE;
- if (buf[0] == '1')
+ if (buf[0] == '1') {
+ s->flags &= ~__CMPXCHG_DOUBLE;
s->flags |= SLAB_DEBUG_FREE;
+ }
return length;
}
SLAB_ATTR(sanity_checks);
@@ -4267,8 +4310,10 @@ static ssize_t trace_store(struct kmem_c
size_t length)
{
s->flags &= ~SLAB_TRACE;
- if (buf[0] == '1')
+ if (buf[0] == '1') {
+ s->flags &= ~__CMPXCHG_DOUBLE;
s->flags |= SLAB_TRACE;
+ }
return length;
}
SLAB_ATTR(trace);
@@ -4285,8 +4330,10 @@ static ssize_t red_zone_store(struct kme
return -EBUSY;

s->flags &= ~SLAB_RED_ZONE;
- if (buf[0] == '1')
+ if (buf[0] == '1') {
+ s->flags &= ~__CMPXCHG_DOUBLE;
s->flags |= SLAB_RED_ZONE;
+ }
calculate_sizes(s, -1);
return length;
}
@@ -4304,8 +4351,10 @@ static ssize_t poison_store(struct kmem_
return -EBUSY;

s->flags &= ~SLAB_POISON;
- if (buf[0] == '1')
+ if (buf[0] == '1') {
+ s->flags &= ~__CMPXCHG_DOUBLE;
s->flags |= SLAB_POISON;
+ }
calculate_sizes(s, -1);
return length;
}
@@ -4323,8 +4372,10 @@ static ssize_t store_user_store(struct k
return -EBUSY;

s->flags &= ~SLAB_STORE_USER;
- if (buf[0] == '1')
+ if (buf[0] == '1') {
+ s->flags &= ~__CMPXCHG_DOUBLE;
s->flags |= SLAB_STORE_USER;
+ }
calculate_sizes(s, -1);
return length;
}
@@ -4497,6 +4548,8 @@ STAT_ATTR(DEACTIVATE_TO_HEAD, deactivate
STAT_ATTR(DEACTIVATE_TO_TAIL, deactivate_to_tail);
STAT_ATTR(DEACTIVATE_REMOTE_FREES, deactivate_remote_frees);
STAT_ATTR(ORDER_FALLBACK, order_fallback);
+STAT_ATTR(CMPXCHG_DOUBLE_CPU_FAIL, cmpxchg_double_cpu_fail);
+STAT_ATTR(CMPXCHG_DOUBLE_FAIL, cmpxchg_double_fail);
#endif

static struct attribute *slab_attrs[] = {
@@ -4554,6 +4607,8 @@ static struct attribute *slab_attrs[] =
&deactivate_to_tail_attr.attr,
&deactivate_remote_frees_attr.attr,
&order_fallback_attr.attr,
+ &cmpxchg_double_fail_attr.attr,
+ &cmpxchg_double_cpu_fail_attr.attr,
#endif
#ifdef CONFIG_FAILSLAB
&failslab_attr.attr,
Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h 2011-05-31 11:50:01.762940481 -0500
+++ linux-2.6/include/linux/slub_def.h 2011-05-31 11:58:01.742937411 -0500
@@ -33,6 +33,7 @@ enum stat_item {
DEACTIVATE_REMOTE_FREES,/* Slab contained remotely freed objects */
ORDER_FALLBACK, /* Number of times fallback was necessary */
CMPXCHG_DOUBLE_CPU_FAIL,/* Failure of this_cpu_cmpxchg_double */
+ CMPXCHG_DOUBLE_FAIL, /* Number of times that cmpxchg double did not match */
NR_SLUB_STAT_ITEMS };

struct kmem_cache_cpu {
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