Commit 6adef3eb authored by Jack Steiner's avatar Jack Steiner Committed by Linus Torvalds
Browse files

cpusets: new round-robin rotor for SLAB allocations 



We have observed several workloads running on multi-node systems where
memory is assigned unevenly across the nodes in the system.  There are
numerous reasons for this but one is the round-robin rotor in
cpuset_mem_spread_node().

For example, a simple test that writes a multi-page file will allocate
pages on nodes 0 2 4 6 ...  Odd nodes are skipped.  (Sometimes it
allocates on odd nodes & skips even nodes).

An example is shown below.  The program "lfile" writes a file consisting
of 10 pages.  The program then mmaps the file & uses get_mempolicy(...,
MPOL_F_NODE) to determine the nodes where the file pages were allocated.
The output is shown below:

	# ./lfile
	 allocated on nodes: 2 4 6 0 1 2 6 0 2

There is a single rotor that is used for allocating both file pages & slab
pages.  Writing the file allocates both a data page & a slab page
(buffer_head).  This advances the RR rotor 2 nodes for each page
allocated.

A quick confirmation seems to confirm this is the cause of the uneven
allocation:

	# echo 0 >/dev/cpuset/memory_spread_slab
	# ./lfile
	 allocated on nodes: 6 7 8 9 0 1 2 3 4 5

This patch introduces a second rotor that is used for slab allocations.

Signed-off-by: default avatarJack Steiner <steiner@sgi.com>
Acked-by: default avatarChristoph Lameter <cl@linux-foundation.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Paul Menage <menage@google.com>
Cc: Jack Steiner <steiner@sgi.com>
Cc: Robin Holt <holt@sgi.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2c488db2

include/linux/cpuset.h

+6 −0
Original line number Diff line number Diff line
@@ -69,6 +69,7 @@ extern void cpuset_task_status_allowed(struct seq_file *m, 
					struct task_struct *task);



extern int cpuset_mem_spread_node(void);

extern int cpuset_slab_spread_node(void);



static inline int cpuset_do_page_mem_spread(void)

{
@@ -194,6 +195,11 @@ static inline int cpuset_mem_spread_node(void) 
	return 0;

}



static inline int cpuset_slab_spread_node(void)

{

	return 0;

}



static inline int cpuset_do_page_mem_spread(void)

{

	return 0;

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1423,6 +1423,7 @@ struct task_struct { 
	nodemask_t mems_allowed;	/* Protected by alloc_lock */

	int mems_allowed_change_disable;

	int cpuset_mem_spread_rotor;

	int cpuset_slab_spread_rotor;

#endif

#ifdef CONFIG_CGROUPS

	/* Control Group info protected by css_set_lock */

kernel/cpuset.c

+16 −4
Original line number Diff line number Diff line
@@ -2469,7 +2469,8 @@ void cpuset_unlock(void) 
}



/**

 * cpuset_mem_spread_node() - On which node to begin search for a page

 * cpuset_mem_spread_node() - On which node to begin search for a file page

 * cpuset_slab_spread_node() - On which node to begin search for a slab page

 *

 * If a task is marked PF_SPREAD_PAGE or PF_SPREAD_SLAB (as for

 * tasks in a cpuset with is_spread_page or is_spread_slab set),
@@ -2494,16 +2495,27 @@ void cpuset_unlock(void) 
 * See kmem_cache_alloc_node().

 */



int cpuset_mem_spread_node(void)

static int cpuset_spread_node(int *rotor)

{

	int node;



	node = next_node(current->cpuset_mem_spread_rotor, current->mems_allowed);

	node = next_node(*rotor, current->mems_allowed);

	if (node == MAX_NUMNODES)

		node = first_node(current->mems_allowed);

	current->cpuset_mem_spread_rotor = node;

	*rotor = node;

	return node;

}



int cpuset_mem_spread_node(void)

{

	return cpuset_spread_node(&current->cpuset_mem_spread_rotor);

}



int cpuset_slab_spread_node(void)

{

	return cpuset_spread_node(&current->cpuset_slab_spread_rotor);

}



EXPORT_SYMBOL_GPL(cpuset_mem_spread_node);



/**

mm/slab.c

+1 −1
Original line number Diff line number Diff line
@@ -3219,7 +3219,7 @@ static void *alternate_node_alloc(struct kmem_cache *cachep, gfp_t flags) 
	nid_alloc = nid_here = numa_node_id();

	get_mems_allowed();

	if (cpuset_do_slab_mem_spread() && (cachep->flags & SLAB_MEM_SPREAD))

		nid_alloc = cpuset_mem_spread_node();

		nid_alloc = cpuset_slab_spread_node();

	else if (current->mempolicy)

		nid_alloc = slab_node(current->mempolicy);

	put_mems_allowed();

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