[PATCH 3/3] slub: fill per cpu partial only when free objects larger than one quarter

[Alex Shi <alex.shi@intel.com>]

From: Alex Shi <alexs@intel.com>

Set selection criteria when fill per cpu partial in slow allocation path,
and check the PCP left space before filling, even maybe the data from another
CPU.
The patch can bring another 1.5% performance increase on netperf loopback
testing for our 4 or 2 sockets machines, include sandbridge, core2

Signed-off-by: Alex Shi <alex.shi@intel.com>
---
 mm/slub.c |   43 +++++++++++++++++++++++++++++++------------
 1 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 65d901f..72df387 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1542,25 +1542,44 @@ static void *get_partial_node(struct kmem_cache *s,
 
 	spin_lock(&n->list_lock);
 	list_for_each_entry_safe(page, page2, &n->partial, lru) {
-		void *t = acquire_slab(s, n, page, object == NULL);
 		int available;
+		void *t;
+		struct page *oldpage;
+		int pobjects;
 
-		if (!t)
-			break;
 
 		if (!object) {
-			c->page = page;
-			c->node = page_to_nid(page);
-			stat(s, ALLOC_FROM_PARTIAL);
-			object = t;
-			available =  page->objects - page->inuse;
+			t = acquire_slab(s, n, page, object == NULL);
+			if (!t)
+				break;
+			else {
+				c->page = page;
+				c->node = page_to_nid(page);
+				stat(s, ALLOC_FROM_PARTIAL);
+				object = t;
+			}
 		} else {
-			page->freelist = t;
-			available = put_cpu_partial(s, page, 0);
+			oldpage = this_cpu_read(s->cpu_slab->partial);
+			pobjects = oldpage ? oldpage->pobjects : 0;
+
+			if (pobjects > s->cpu_partial / 2)
+				break;
+
+			available =  page->objects - page->inuse;
+			if (available >= s->cpu_partial / 4) {
+				t = acquire_slab(s, n, page, object == NULL);
+				if (!t)
+					break;
+				else {
+					page->freelist = t;
+					if (put_cpu_partial(s, page, 0) >
+							s->cpu_partial / 2)
+						break;
+				}
+			}
 		}
-		if (kmem_cache_debug(s) || available > s->cpu_partial / 2)
+		if (kmem_cache_debug(s))
 			break;
-
 	}
 	spin_unlock(&n->list_lock);
 	return object;
-- 
1.7.0.1

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