Re: [RT LATENCY] 249 microsecond latency caused by slub'sunfreeze_partials() code.

From: Christoph Lameter
Date: Mon Apr 01 2013 - 11:40:31 EST


Subject: slub: Fix object counts in acquire_slab V2

It seems that we were overallocating objects from the slab queues
since get_partial_node() assumed that page->inuse was undisturbed by
acquire_slab(). Save the # of objects in page->lru.next in acquire_slab()
and pass it to get_partial_node() that way.

I have a vague memory that Joonsoo also ran into this issue awhile back.

Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>

Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c 2013-03-28 12:14:26.958358688 -0500
+++ linux/mm/slub.c 2013-04-01 10:23:24.677584499 -0500
@@ -1498,6 +1498,7 @@ static inline void *acquire_slab(struct
void *freelist;
unsigned long counters;
struct page new;
+ unsigned long objects;

/*
* Zap the freelist and set the frozen bit.
@@ -1507,6 +1508,7 @@ static inline void *acquire_slab(struct
freelist = page->freelist;
counters = page->counters;
new.counters = counters;
+ objects = page->inuse;
if (mode) {
new.inuse = page->objects;
new.freelist = NULL;
@@ -1524,6 +1526,7 @@ static inline void *acquire_slab(struct
return NULL;

remove_partial(n, page);
+ page->lru.next = (void *)objects;
WARN_ON(!freelist);
return freelist;
}
@@ -1565,7 +1568,7 @@ static void *get_partial_node(struct kme
c->page = page;
stat(s, ALLOC_FROM_PARTIAL);
object = t;
- available = page->objects - page->inuse;
+ available = page->objects - (unsigned long)page->lru.next;
} else {
available = put_cpu_partial(s, page, 0);
stat(s, CPU_PARTIAL_NODE);
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