[RFC 10/26] SLUB: Trigger defragmentation from memory reclaim

Christoph Lameter
2007-09-01T01:46:58Z

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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
by objects being freed. 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.

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 | 27 ++++++++++++++++++++-------
4 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index 59375ef..fb58e63 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -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);
}

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a396aac..9fbb6ba 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1202,7 +1202,7 @@ int in_gate_area_no_task(unsigned long addr);
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 *zone);
void drop_pagecache(void);
void drop_slab(void);

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 848e9a7..7d8ec17 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -61,6 +61,7 @@ void kmem_cache_free(struct kmem_cache *, void *);
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
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d419e10..c6882d8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -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 scanned, gfp_t gfp_mask,
shrinker->nr += total_scan;
}
up_read(&shrinker_rwsem);
+ if (gfp_mask & __GFP_FS)
+ kmem_cache_defrag(zone ? zone_to_nid(zone) : -1);
return ret;
}

@@ -1151,7 +1161,8 @@ unsigned long try_to_free_pages(struct zone **zones, int order, gfp_t gfp_mask)
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;
@@ -1321,7 +1332,7 @@ 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->all_unreclaimable)
@@ -1559,7 +1570,7 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
/* 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;

@@ -1597,7 +1608,7 @@ unsigned long shrink_all_memory(unsigned long nr_pages)

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;
@@ -1614,7 +1625,8 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
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);
}
@@ -1774,7 +1786,8 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
* 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)
;
--
1.5.2.4

--