In preparation for enabling defragmentation of slab pages.
"defrag_used_ratio" is used to set the threshold at which
defragmentation should be attempted on a slab page.
"defrag_used_ratio" is a percentage in the range of 0 - 100 (inclusive).
If less than that percentage of slots in a slab page are in use then the
slab page will become subject to defragmentation.
Add a defrag ratio field and set it to 30% by default. A limit of 30%
specifies that more than 3 out of 10 available slots for objects need to
be in use otherwise slab defragmentation will be attempted on the
remaining objects.
Co-developed-by: Christoph Lameter <c...@linux.com>
Signed-off-by: Tobin C. Harding <to...@kernel.org>
---
Documentation/ABI/testing/sysfs-kernel-slab | 14 ++++++++++++
include/linux/slub_def.h | 7 ++++++
mm/slub.c | 24 +++++++++++++++++++++
3 files changed, 45 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-kernel-slab
b/Documentation/ABI/testing/sysfs-kernel-slab
index 29601d93a1c2..7770c03be6b4 100644
--- a/Documentation/ABI/testing/sysfs-kernel-slab
+++ b/Documentation/ABI/testing/sysfs-kernel-slab
@@ -180,6 +180,20 @@ Description:
list. It can be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
+What: /sys/kernel/slab/cache/defrag_used_ratio
+Date: February 2019
+KernelVersion: 5.0
+Contact: Christoph Lameter <c...@linux-foundation.org>
+ Pekka Enberg <penb...@cs.helsinki.fi>,
+Description:
+ The defrag_used_ratio file allows the control of how aggressive
+ slab fragmentation reduction works at reclaiming objects from
+ sparsely populated slabs. This is a percentage. If a slab has
+ less than this percentage of objects allocated then reclaim will
+ attempt to reclaim objects so that the whole slab page can be
+ freed. 0% specifies no reclaim attempt (defrag disabled), 100%
+ specifies attempt to reclaim all pages. The default is 30%.
+
What: /sys/kernel/slab/cache/deactivate_to_tail
Date: February 2008
KernelVersion: 2.6.25
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index a7340a1ed5dc..6da6197ca973 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -107,6 +107,13 @@ struct kmem_cache {
unsigned int red_left_pad; /* Left redzone padding size */
const char *name; /* Name (only for display!) */
struct list_head list; /* List of slab caches */
+ int defrag_used_ratio; /*
+ * Ratio used to check against the
+ * percentage of objects allocated in a
+ * slab page. If less than this ratio
+ * is allocated then reclaim attempts
+ * are made.
+ */
#ifdef CONFIG_SYSFS
struct kobject kobj; /* For sysfs */
struct work_struct kobj_remove_work;
diff --git a/mm/slub.c b/mm/slub.c
index f37103e22d3f..515db0f36c55 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3642,6 +3642,7 @@ static int kmem_cache_open(struct kmem_cache *s,
slab_flags_t flags)
set_cpu_partial(s);
+ s->defrag_used_ratio = 30;
#ifdef CONFIG_NUMA
s->remote_node_defrag_ratio = 1000;
#endif
@@ -5261,6 +5262,28 @@ static ssize_t destroy_by_rcu_show(struct kmem_cache *s,
char *buf)
}
SLAB_ATTR_RO(destroy_by_rcu);
+static ssize_t defrag_used_ratio_show(struct kmem_cache *s, char *buf)
+{
+ return sprintf(buf, "%d\n", s->defrag_used_ratio);
+}
+
+static ssize_t defrag_used_ratio_store(struct kmem_cache *s,
+ const char *buf, size_t length)
+{
+ unsigned long ratio;
+ int err;
+
+ err = kstrtoul(buf, 10, &ratio);
+ if (err)
+ return err;
+
+ if (ratio <= 100)
+ s->defrag_used_ratio = ratio;
+
+ return length;
+}
+SLAB_ATTR(defrag_used_ratio);
+
#ifdef CONFIG_SLUB_DEBUG
static ssize_t slabs_show(struct kmem_cache *s, char *buf)
{
@@ -5585,6 +5608,7 @@ static struct attribute *slab_attrs[] = {
&validate_attr.attr,
&alloc_calls_attr.attr,
&free_calls_attr.attr,
+ &defrag_used_ratio_attr.attr,
#endif
#ifdef CONFIG_ZONE_DMA
&cache_dma_attr.attr,
--
2.21.0
