Commit 02d7633f authored May 17, 2012 by Joonsoo Kim Committed by Pekka Enberg May 18, 2012

slub: fix a memory leak in get_partial_node()



In the case which is below,

1. acquire slab for cpu partial list
2. free object to it by remote cpu
3. page->freelist = t

then memory leak is occurred.

Change acquire_slab() not to zap freelist when it works for cpu partial list.
I think it is a sufficient solution for fixing a memory leak.

Below is output of 'slabinfo -r kmalloc-256'
when './perf stat -r 30 hackbench 50 process 4000 > /dev/null' is done.

***Vanilla***
Sizes (bytes)     Slabs              Debug                Memory
------------------------------------------------------------------------
Object :     256  Total  :     468   Sanity Checks : Off  Total: 3833856
SlabObj:     256  Full   :     111   Redzoning     : Off  Used : 2004992
SlabSiz:    8192  Partial:     302   Poisoning     : Off  Loss : 1828864
Loss   :       0  CpuSlab:      55   Tracking      : Off  Lalig:       0
Align  :       8  Objects:      32   Tracing       : Off  Lpadd:       0

***Patched***
Sizes (bytes)     Slabs              Debug                Memory
------------------------------------------------------------------------
Object :     256  Total  :     300   Sanity Checks : Off  Total: 2457600
SlabObj:     256  Full   :     204   Redzoning     : Off  Used : 2348800
SlabSiz:    8192  Partial:      33   Poisoning     : Off  Loss :  108800
Loss   :       0  CpuSlab:      63   Tracking      : Off  Lalig:       0
Align  :       8  Objects:      32   Tracing       : Off  Lpadd:       0

Total and loss number is the impact of this patch.

Cc: <stable@vger.kernel.org>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Joonsoo Kim <js1304@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

parent 4053497d

mm/slub.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -1514,15 +1514,19 @@ static inline void acquire_slab(struct kmem_cache s,
		freelist = page->freelist;
		counters = page->counters;
		new.counters = counters;
		if (mode)
		if (mode) {
		new.inuse = page->objects;
		new.freelist = NULL;
		} else {
		new.freelist = freelist;
		}

		VM_BUG_ON(new.frozen);
		new.frozen = 1;

		} while (!__cmpxchg_double_slab(s, page,
		freelist, counters,
		NULL, new.counters,
		new.freelist, new.counters,
		"lock and freeze"));

		remove_partial(n, page);
		@@ -1564,7 +1568,6 @@ static void get_partial_node(struct kmem_cache s,
		object = t;
		available = page->objects - page->inuse;
		} else {
		page->freelist = t;
		available = put_cpu_partial(s, page, 0);
		stat(s, CPU_PARTIAL_NODE);
		}