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Subject[PATCH UPDATED x86/mm] x86-64, NUMA: Better explain numa_distance handling
From 615e1632e55b6b8fb52da00c5e8540ef159f759b Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Wed, 2 Mar 2011 11:32:47 +0100

Handling of out-of-bounds distances and allocation failure can use
better documentation. Add it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>
---
Sorry, sent out the wrong version. This one is a bit more detailed
and the version I put into the tree.
Thanks.

arch/x86/mm/numa_64.c | 11 ++++++++++-
arch/x86/mm/numa_emulation.c | 6 +++++-
2 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/arch/x86/mm/numa_64.c b/arch/x86/mm/numa_64.c
index 541746f..74064e8 100644
--- a/arch/x86/mm/numa_64.c
+++ b/arch/x86/mm/numa_64.c
@@ -392,11 +392,12 @@ void __init numa_reset_distance(void)
{
size_t size = numa_distance_cnt * numa_distance_cnt * sizeof(numa_distance[0]);

+ /* numa_distance could be 1LU marking allocation failure, test cnt */
if (numa_distance_cnt)
memblock_x86_free_range(__pa(numa_distance),
__pa(numa_distance) + size);
numa_distance_cnt = 0;
- numa_distance = NULL;
+ numa_distance = NULL; /* enable table creation */
}

static int __init numa_alloc_distance(void)
@@ -447,6 +448,14 @@ static int __init numa_alloc_distance(void)
* Set the distance from node @from to @to to @distance. If distance table
* doesn't exist, one which is large enough to accomodate all the currently
* known nodes will be created.
+ *
+ * If such table cannot be allocated, a warning is printed and further
+ * calls are ignored until the distance table is reset with
+ * numa_reset_distance().
+ *
+ * If @from or @to is higher than the highest known node at the time of
+ * table creation or @distance doesn't make sense, the call is ignored.
+ * This is to allow simplification of specific NUMA config implementations.
*/
void __init numa_set_distance(int from, int to, int distance)
{
diff --git a/arch/x86/mm/numa_emulation.c b/arch/x86/mm/numa_emulation.c
index 0afa25d..aeecea9 100644
--- a/arch/x86/mm/numa_emulation.c
+++ b/arch/x86/mm/numa_emulation.c
@@ -379,7 +379,11 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
if (emu_nid_to_phys[i] == NUMA_NO_NODE)
emu_nid_to_phys[i] = 0;

- /* transform distance table */
+ /*
+ * Transform distance table. numa_set_distance() ignores all
+ * out-of-bound distances. Just call it for every possible node
+ * combination.
+ */
numa_reset_distance();
for (i = 0; i < MAX_NUMNODES; i++) {
for (j = 0; j < MAX_NUMNODES; j++) {
--
1.7.1


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