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Subject[patch 12/23] SLUB: Trigger defragmentation from memory reclaim
This patch triggers slab defragmentation from memory reclaim.
The logical point for this is after slab shrinking was performed in
vmscan.c. At that point the fragmentation ratio of a slab was increased
because objects were freed via the LRUs. So we call kmem_cache_defrag from
there.

slab_shrink() from vmscan.c is called in some contexts to do
global shrinking of slabs and in others to do shrinking for
a particular zone. Pass the zone to slab_shrink, so that slab_shrink
can call kmem_cache_defrag() and restrict the defragmentation to
the node that is under memory pressure.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
fs/drop_caches.c | 2 +-
include/linux/mm.h | 2 +-
include/linux/slab.h | 1 +
mm/vmscan.c | 26 +++++++++++++++++++-------
4 files changed, 22 insertions(+), 9 deletions(-)

Index: linux-2.6/fs/drop_caches.c
===================================================================
--- linux-2.6.orig/fs/drop_caches.c 2007-08-29 19:30:53.000000000 -0700
+++ linux-2.6/fs/drop_caches.c 2007-11-06 12:53:40.000000000 -0800
@@ -50,7 +50,7 @@ void drop_slab(void)
int nr_objects;

do {
- nr_objects = shrink_slab(1000, GFP_KERNEL, 1000);
+ nr_objects = shrink_slab(1000, GFP_KERNEL, 1000, NULL);
} while (nr_objects > 10);
}

Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h 2007-11-06 12:33:55.000000000 -0800
+++ linux-2.6/include/linux/mm.h 2007-11-06 12:54:11.000000000 -0800
@@ -1118,7 +1118,7 @@ int in_gate_area_no_task(unsigned long a
int drop_caches_sysctl_handler(struct ctl_table *, int, struct file *,
void __user *, size_t *, loff_t *);
unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
- unsigned long lru_pages);
+ unsigned long lru_pages, struct zone *z);
void drop_pagecache(void);
void drop_slab(void);

Index: linux-2.6/include/linux/slab.h
===================================================================
--- linux-2.6.orig/include/linux/slab.h 2007-11-06 12:37:51.000000000 -0800
+++ linux-2.6/include/linux/slab.h 2007-11-06 12:53:40.000000000 -0800
@@ -63,6 +63,7 @@ void kmem_cache_free(struct kmem_cache *
unsigned int kmem_cache_size(struct kmem_cache *);
const char *kmem_cache_name(struct kmem_cache *);
int kmem_ptr_validate(struct kmem_cache *cachep, const void *ptr);
+int kmem_cache_defrag(int node);

/*
* Please use this macro to create slab caches. Simply specify the
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c 2007-10-25 18:28:41.000000000 -0700
+++ linux-2.6/mm/vmscan.c 2007-11-06 12:55:25.000000000 -0800
@@ -150,10 +150,18 @@ EXPORT_SYMBOL(unregister_shrinker);
* are eligible for the caller's allocation attempt. It is used for balancing
* slab reclaim versus page reclaim.
*
+ * zone is the zone for which we are shrinking the slabs. If the intent
+ * is to do a global shrink then zone may be NULL. Specification of a
+ * zone is currently only used to limit slab defragmentation to a NUMA node.
+ * The performace of shrink_slab would be better (in particular under NUMA)
+ * if it could be targeted as a whole to the zone that is under memory
+ * pressure but the VFS infrastructure does not allow that at the present
+ * time.
+ *
* Returns the number of slab objects which we shrunk.
*/
unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
- unsigned long lru_pages)
+ unsigned long lru_pages, struct zone *zone)
{
struct shrinker *shrinker;
unsigned long ret = 0;
@@ -210,6 +218,8 @@ unsigned long shrink_slab(unsigned long
shrinker->nr += total_scan;
}
up_read(&shrinker_rwsem);
+ if (gfp_mask & __GFP_FS)
+ kmem_cache_defrag(zone ? zone_to_nid(zone) : -1);
return ret;
}

@@ -1241,7 +1251,7 @@ unsigned long try_to_free_pages(struct z
if (!priority)
disable_swap_token();
nr_reclaimed += shrink_zones(priority, zones, &sc);
- shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
+ shrink_slab(sc.nr_scanned, gfp_mask, lru_pages, NULL);
if (reclaim_state) {
nr_reclaimed += reclaim_state->reclaimed_slab;
reclaim_state->reclaimed_slab = 0;
@@ -1419,7 +1429,7 @@ loop_again:
nr_reclaimed += shrink_zone(priority, zone, &sc);
reclaim_state->reclaimed_slab = 0;
nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
- lru_pages);
+ lru_pages, zone);
nr_reclaimed += reclaim_state->reclaimed_slab;
total_scanned += sc.nr_scanned;
if (zone_is_all_unreclaimable(zone))
@@ -1658,7 +1668,7 @@ unsigned long shrink_all_memory(unsigned
/* If slab caches are huge, it's better to hit them first */
while (nr_slab >= lru_pages) {
reclaim_state.reclaimed_slab = 0;
- shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
+ shrink_slab(nr_pages, sc.gfp_mask, lru_pages, NULL);
if (!reclaim_state.reclaimed_slab)
break;

@@ -1696,7 +1706,7 @@ unsigned long shrink_all_memory(unsigned

reclaim_state.reclaimed_slab = 0;
shrink_slab(sc.nr_scanned, sc.gfp_mask,
- count_lru_pages());
+ count_lru_pages(), NULL);
ret += reclaim_state.reclaimed_slab;
if (ret >= nr_pages)
goto out;
@@ -1713,7 +1723,8 @@ unsigned long shrink_all_memory(unsigned
if (!ret) {
do {
reclaim_state.reclaimed_slab = 0;
- shrink_slab(nr_pages, sc.gfp_mask, count_lru_pages());
+ shrink_slab(nr_pages, sc.gfp_mask,
+ count_lru_pages(), NULL);
ret += reclaim_state.reclaimed_slab;
} while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
}
@@ -1875,7 +1886,8 @@ static int __zone_reclaim(struct zone *z
* Note that shrink_slab will free memory on all zones and may
* take a long time.
*/
- while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
+ while (shrink_slab(sc.nr_scanned, gfp_mask, order,
+ zone) &&
zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
slab_reclaimable - nr_pages)
;
--
-
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