[Xen-devel] [PATCH] page-alloc: Clamp get_free_buddy() to online nodes

Andrew Cooper posted 1 patch 17 weeks ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/xen tags/patchew/20190624180128.5328-1-andrew.cooper3@citrix.com
xen/common/page_alloc.c    | 7 ++++++-
xen/include/xen/nodemask.h | 6 ++++++
2 files changed, 12 insertions(+), 1 deletion(-)

[Xen-devel] [PATCH] page-alloc: Clamp get_free_buddy() to online nodes

Posted by Andrew Cooper 17 weeks ago
d->node_affinity defaults to NODE_MASK_ALL which has bits set outside of
node_online_map.  This in turn causes the loop in get_free_buddy() to waste
effort iterating over offline nodes.

Always clamp d->node_affinity to node_online_map when in use.

This in turn involves implementing nodes_copy() which was previously missing.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien.grall@arm.com>
CC: George Dunlap <george.dunlap@eu.citrix.com>

This patch hides the issue identified in the "UBSAN report in find_next_bit()"
so probably doesn't want applying until that is resolved.

A lower overhead option would be to do:

nodes_and(nodemask, node_online_map, d ? d->node_affinity : node_online_map);

however this doesn't work because the nodeset_t API has a hidden &(param)
throughout the API.  I've got half a mind to undo this nonsense and have
nodemask_t work in exactly the same way as cpumask_t.
---
 xen/common/page_alloc.c    | 7 ++++++-
 xen/include/xen/nodemask.h | 6 ++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 7825fd8c42..cec1b15d5b 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -811,11 +811,16 @@ static struct page_info *get_free_buddy(unsigned int zone_lo,
                                         const struct domain *d)
 {
     nodeid_t first_node, node = MEMF_get_node(memflags), req_node = node;
-    nodemask_t nodemask = d ? d->node_affinity : node_online_map;
+    nodemask_t nodemask;
     unsigned int j, zone, nodemask_retry = 0;
     struct page_info *pg;
     bool use_unscrubbed = (memflags & MEMF_no_scrub);
 
+    /* Clamp nodemask to node_online_map and optionally d->node_affinity. */
+    nodes_copy(nodemask, node_online_map);
+    if ( d )
+        nodes_and(nodemask, nodemask, d->node_affinity);
+
     if ( node == NUMA_NO_NODE )
     {
         if ( d != NULL )
diff --git a/xen/include/xen/nodemask.h b/xen/include/xen/nodemask.h
index e287399352..e83cfe2439 100644
--- a/xen/include/xen/nodemask.h
+++ b/xen/include/xen/nodemask.h
@@ -189,6 +189,12 @@ static inline int __nodes_weight(const nodemask_t *srcp, int nbits)
 	return bitmap_weight(srcp->bits, nbits);
 }
 
+#define nodes_copy(dst, src) __nodes_copy(&(dst), &(src))
+static inline void __nodes_copy(nodemask_t *dst, nodemask_t *src)
+{
+	return bitmap_copy(dst->bits, src->bits, MAX_NUMNODES);
+}
+
 #define nodes_shift_right(dst, src, n) \
 			__nodes_shift_right(&(dst), &(src), (n), MAX_NUMNODES)
 static inline void __nodes_shift_right(nodemask_t *dstp,
-- 
2.11.0


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Re: [Xen-devel] [PATCH] page-alloc: Clamp get_free_buddy() to online nodes

Posted by Jan Beulich 17 weeks ago
>>> On 24.06.19 at 20:01, <andrew.cooper3@citrix.com> wrote:
> This patch hides the issue identified in the "UBSAN report in find_next_bit()"
> so probably doesn't want applying until that is resolved.

It does so on systems with less than 64 nodes, afaict.

> A lower overhead option would be to do:
> 
> nodes_and(nodemask, node_online_map, d ? d->node_affinity : node_online_map);
> 
> however this doesn't work because the nodeset_t API has a hidden &(param)
> throughout the API.  I've got half a mind to undo this nonsense and have
> nodemask_t work in exactly the same way as cpumask_t.

Right, we should do such a transformation eventually.

> --- a/xen/include/xen/nodemask.h
> +++ b/xen/include/xen/nodemask.h
> @@ -189,6 +189,12 @@ static inline int __nodes_weight(const nodemask_t *srcp, int nbits)
>  	return bitmap_weight(srcp->bits, nbits);
>  }
>  
> +#define nodes_copy(dst, src) __nodes_copy(&(dst), &(src))
> +static inline void __nodes_copy(nodemask_t *dst, nodemask_t *src)
> +{
> +	return bitmap_copy(dst->bits, src->bits, MAX_NUMNODES);
> +}

Rather than introducing this, I think structure assignment is meant
to be used (as was the case prior to your change). But if you really
feel like introducing this, then please constify "src". With either
adjustment made,
Reviewed-by: Jan Beulich <jbeulich@suse.com>

Jan



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