Re: [PATCH] cgroup: prefer [kv]zalloc over [kv]malloc+memset in memory controller code.

[Jesper Juhl <jj@chaosbits.net>]

On Mon, 1 Nov 2010, Johannes Weiner wrote:

> On Mon, Nov 01, 2010 at 08:40:56PM +0100, Jesper Juhl wrote:
> > Hi (please CC me on replies),
> > 
> > 
> > Apologies to those who receive this multiple times. I screwed up the To: 
> > field in my original mail :-(
> > 
> > 
> > In mem_cgroup_alloc() we currently do either kmalloc() or vmalloc() then 
> > followed by memset() to zero the memory. This can be more efficiently 
> > achieved by using kzalloc() and vzalloc().
> > 
> > 
> > Signed-off-by: Jesper Juhl <jj@chaosbits.net>
> 
> Looks good to me, but there is also the memset after kmalloc in
> alloc_mem_cgroup_per_zone_info(). 

Dang, I missed that one. Thanks for pointing it out.

Hmm, I'm wondering if we should perhaps add kzalloc_node()/vzalloc_node() 
just like kzalloc() and vzalloc()..


> Can you switch that over as well in
> this patch?  You can pass __GFP_ZERO to kmalloc_node() for zeroing.
> 

Sure thing.


Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
 memcontrol.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9a99cfa..bc32ffe 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4169,13 +4169,11 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
 	 */
 	if (!node_state(node, N_NORMAL_MEMORY))
 		tmp = -1;
-	pn = kmalloc_node(sizeof(*pn), GFP_KERNEL, tmp);
+	pn = kmalloc_node(sizeof(*pn), GFP_KERNEL|__GFP_ZERO, tmp);
 	if (!pn)
 		return 1;
 
 	mem->info.nodeinfo[node] = pn;
-	memset(pn, 0, sizeof(*pn));
-
 	for (zone = 0; zone < MAX_NR_ZONES; zone++) {
 		mz = &pn->zoneinfo[zone];
 		for_each_lru(l)
@@ -4199,14 +4197,13 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 
 	/* Can be very big if MAX_NUMNODES is very big */
 	if (size < PAGE_SIZE)
-		mem = kmalloc(size, GFP_KERNEL);
+		mem = kzalloc(size, GFP_KERNEL);
 	else
-		mem = vmalloc(size);
+		mem = vzalloc(size);
 
 	if (!mem)
 		return NULL;
 
-	memset(mem, 0, size);
 	mem->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
 	if (!mem->stat) {
 		if (size < PAGE_SIZE)


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Jesper Juhl <jj@chaosbits.net>             http://www.chaosbits.net/
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