Lee Schermerhorn
2009-08-28T16:03:32Z

[PATCH 3/6] hugetlb: derive huge pages nodes allowed from task mempolicy

Against: 2.6.31-rc7-mmotm-090827-0057

V2:
+ cleaned up comments, removed some deemed unnecessary,
add some suggested by review
+ removed check for !current in huge_mpol_nodes_allowed().
+ added 'current->comm' to warning message in huge_mpol_nodes_allowed().
+ added VM_BUG_ON() assertion in hugetlb.c next_node_allowed() to
catch out of range node id.
+ add examples to patch description

V3: Factored this patch from V2 patch 2/3

V4: added back missing "kfree(nodes_allowed)" in set_max_nr_hugepages()

V5: remove internal '\n' from printk in huge_mpol_nodes_allowed()

This patch derives a "nodes_allowed" node mask from the numa
mempolicy of the task modifying the number of persistent huge
pages to control the allocation, freeing and adjusting of surplus
huge pages. This mask is derived as follows:

* For "default" [NULL] task mempolicy, a NULL nodemask_t pointer
is produced. This will cause the hugetlb subsystem to use
node_online_map as the "nodes_allowed". This preserves the
behavior before this patch.
* For "preferred" mempolicy, including explicit local allocation,
a nodemask with the single preferred node will be produced.
"local" policy will NOT track any internode migrations of the
task adjusting nr_hugepages.
* For "bind" and "interleave" policy, the mempolicy's nodemask
will be used.
* Other than to inform the construction of the nodes_allowed node
mask, the actual mempolicy mode is ignored. That is, all modes
behave like interleave over the resulting nodes_allowed mask
with no "fallback".

Notes:

1) This patch introduces a subtle change in behavior: huge page
allocation and freeing will be constrained by any mempolicy
that the task adjusting the huge page pool inherits from its
parent. This policy could come from a distant ancestor. The
adminstrator adjusting the huge page pool without explicitly
specifying a mempolicy via numactl might be surprised by this.
Additionaly, any mempolicy specified by numactl will be
constrained by the cpuset in which numactl is invoked.
Using sysfs per node hugepages attributes to adjust the per
node persistent huge pages count [subsequent patch] ignores
mempolicy and cpuset constraints.

2) Hugepages allocated at boot time use the node_online_map.
An additional patch could implement a temporary boot time
huge pages nodes_allowed command line parameter.

3) Using mempolicy to control persistent huge page allocation
and freeing requires no change to hugeadm when invoking
it via numactl, as shown in the examples below. However,
hugeadm could be enhanced to take the allowed nodes as an
argument and set its task mempolicy itself. This would allow
it to detect and warn about any non-default mempolicy that it
inherited from its parent, thus alleviating the issue described
in Note 1 above.

See the updated documentation [next patch] for more information
about the implications of this patch.

Examples:

Starting with:

Node 0 HugePages_Total: 0
Node 1 HugePages_Total: 0
Node 2 HugePages_Total: 0
Node 3 HugePages_Total: 0

Default behavior [with or without this patch] balances persistent
hugepage allocation across nodes [with sufficient contiguous memory]:

hugeadm --pool-pages-min=2048Kb:32

yields:

Node 0 HugePages_Total: 8
Node 1 HugePages_Total: 8
Node 2 HugePages_Total: 8
Node 3 HugePages_Total: 8

Applying mempolicy--e.g., with numactl [using '-m' a.k.a.
'--membind' because it allows multiple nodes to be specified
and it's easy to type]--we can allocate huge pages on
individual nodes or sets of nodes. So, starting from the
condition above, with 8 huge pages per node:

numactl -m 2 hugeadm --pool-pages-min=2048Kb:+8

yields:

Node 0 HugePages_Total: 8
Node 1 HugePages_Total: 8
Node 2 HugePages_Total: 16
Node 3 HugePages_Total: 8

The incremental 8 huge pages were restricted to node 2 by the
specified mempolicy.

Similarly, we can use mempolicy to free persistent huge pages
from specified nodes:

numactl -m 0,1 hugeadm --pool-pages-min=2048Kb:-8

yields:

Node 0 HugePages_Total: 4
Node 1 HugePages_Total: 4
Node 2 HugePages_Total: 16
Node 3 HugePages_Total: 8

The 8 huge pages freed were balanced over nodes 0 and 1.

Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

include/linux/mempolicy.h | 3 ++
mm/hugetlb.c | 14 ++++++----
mm/mempolicy.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 73 insertions(+), 5 deletions(-)

Index: linux-2.6.31-rc7-mmotm-090827-0057/mm/mempolicy.c
===================================================================
--- linux-2.6.31-rc7-mmotm-090827-0057.orig/mm/mempolicy.c 2009-08-28 09:21:20.000000000 -0400
+++ linux-2.6.31-rc7-mmotm-090827-0057/mm/mempolicy.c 2009-08-28 09:21:28.000000000 -0400
@@ -1564,6 +1564,67 @@ struct zonelist *huge_zonelist(struct vm
}
return zl;
}
+
+/*
+ * huge_mpol_nodes_allowed -- mempolicy extension for huge pages.
+ *
+ * Returns a [pointer to a] nodelist based on the current task's mempolicy
+ * to constraing the allocation and freeing of persistent huge pages
+ * 'Preferred', 'local' and 'interleave' mempolicy will behave more like
+ * 'bind' policy in this context. An attempt to allocate a persistent huge
+ * page will never "fallback" to another node inside the buddy system
+ * allocator.
+ *
+ * If the task's mempolicy is "default" [NULL], just return NULL for
+ * default behavior. Otherwise, extract the policy nodemask for 'bind'
+ * or 'interleave' policy or construct a nodemask for 'preferred' or
+ * 'local' policy and return a pointer to a kmalloc()ed nodemask_t.
+ *
+ * N.B., it is the caller's responsibility to free a returned nodemask.
+ */
+nodemask_t *huge_mpol_nodes_allowed(void)
+{
+ nodemask_t *nodes_allowed = NULL;
+ struct mempolicy *mempolicy;
+ int nid;
+
+ if (!current->mempolicy)
+ return NULL;
+
+ mpol_get(current->mempolicy);
+ nodes_allowed = kmalloc(sizeof(*nodes_allowed), GFP_KERNEL);
+ if (!nodes_allowed) {
+ printk(KERN_WARNING "%s unable to allocate nodes allowed mask "
+ "for huge page allocation. Falling back to default.\n",
+ current->comm);
+ goto out;
+ }
+ nodes_clear(*nodes_allowed);
+
+ mempolicy = current->mempolicy;
+ switch (mempolicy->mode) {
+ case MPOL_PREFERRED:
+ if (mempolicy->flags & MPOL_F_LOCAL)
+ nid = numa_node_id();
+ else
+ nid = mempolicy->v.preferred_node;
+ node_set(nid, *nodes_allowed);
+ break;
+
+ case MPOL_BIND:
+ /* Fall through */
+ case MPOL_INTERLEAVE:
+ *nodes_allowed = mempolicy->v.nodes;
+ break;
+
+ default:
+ BUG();
+ }
+
+out:
+ mpol_put(current->mempolicy);
+ return nodes_allowed;
+}
#endif

/* Allocate a page in interleaved policy.
Index: linux-2.6.31-rc7-mmotm-090827-0057/include/linux/mempolicy.h
===================================================================
--- linux-2.6.31-rc7-mmotm-090827-0057.orig/include/linux/mempolicy.h 2009-08-28 09:21:20.000000000 -0400
+++ linux-2.6.31-rc7-mmotm-090827-0057/include/linux/mempolicy.h 2009-08-28 09:21:28.000000000 -0400
@@ -201,6 +201,7 @@ extern void mpol_fix_fork_child_flag(str
extern struct zonelist *huge_zonelist(struct vm_area_struct *vma,
unsigned long addr, gfp_t gfp_flags,
struct mempolicy **mpol, nodemask_t **nodemask);
+extern nodemask_t *huge_mpol_nodes_allowed(void);
extern unsigned slab_node(struct mempolicy *policy);

extern enum zone_type policy_zone;
@@ -328,6 +329,8 @@ static inline struct zonelist *huge_zone
return node_zonelist(0, gfp_flags);
}

+static inline nodemask_t *huge_mpol_nodes_allowed(void) { return NULL; }
+
static inline int do_migrate_pages(struct mm_struct *mm,
const nodemask_t *from_nodes,
const nodemask_t *to_nodes, int flags)
Index: linux-2.6.31-rc7-mmotm-090827-0057/mm/hugetlb.c
===================================================================
--- linux-2.6.31-rc7-mmotm-090827-0057.orig/mm/hugetlb.c 2009-08-28 09:21:26.000000000 -0400
+++ linux-2.6.31-rc7-mmotm-090827-0057/mm/hugetlb.c 2009-08-28 09:21:28.000000000 -0400
@@ -1248,10 +1248,13 @@ static int adjust_pool_surplus(struct hs
static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count)
{
unsigned long min_count, ret;
+ nodemask_t *nodes_allowed;

if (h->order >= MAX_ORDER)
return h->max_huge_pages;

+ nodes_allowed = huge_mpol_nodes_allowed();
+
/*
* Increase the pool size
* First take pages out of surplus state. Then make up the
@@ -1265,7 +1268,7 @@ static unsigned long set_max_huge_pages(
*/
spin_lock(&hugetlb_lock);
while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
- if (!adjust_pool_surplus(h, NULL, -1))
+ if (!adjust_pool_surplus(h, nodes_allowed, -1))
break;
}

@@ -1276,7 +1279,7 @@ static unsigned long set_max_huge_pages(
* and reducing the surplus.
*/
spin_unlock(&hugetlb_lock);
- ret = alloc_fresh_huge_page(h, NULL);
+ ret = alloc_fresh_huge_page(h, nodes_allowed);
spin_lock(&hugetlb_lock);
if (!ret)
goto out;
@@ -1300,18 +1303,19 @@ static unsigned long set_max_huge_pages(
*/
min_count = h->resv_huge_pages + h->nr_huge_pages - h->free_huge_pages;
min_count = max(count, min_count);
- try_to_free_low(h, min_count, NULL);
+ try_to_free_low(h, min_count, nodes_allowed);
while (min_count < persistent_huge_pages(h)) {
- if (!free_pool_huge_page(h, NULL, 0))
+ if (!free_pool_huge_page(h, nodes_allowed, 0))
break;
}
while (count < persistent_huge_pages(h)) {
- if (!adjust_pool_surplus(h, NULL, 1))
+ if (!adjust_pool_surplus(h, nodes_allowed, 1))
break;
}
out:
ret = persistent_huge_pages(h);
spin_unlock(&hugetlb_lock);
+ kfree(nodes_allowed);
return ret;
}