[PATCH] pipe: Prefer mempolicy node for metadata allocations

[PATCH] pipe: Prefer mempolicy node for metadata allocations

[Andrea Righi]

Generic slab allocations can reuse partial slabs from another NUMA node,
even when a pipe workload is bound to one node. Pipe metadata is shared
between senders and receivers and accessed throughout the pipe lifetime.
Reusing remote metadata can therefore make an IPC workload pay remote
access and coherence costs on every exchange.

The target use case is a workload that binds its workers and memory to
one NUMA node with numactl. The policy node is then a useful placement
hint for shared pipe metadata.

Allocate pipe_inode_info and its descriptor array on the node selected
by the caller's memory policy. Apply the same preference when replacing
slab-sized descriptor arrays during ring resizing. An explicit node lets
SLUB try local allocations before reusing remote partial slabs.

For descriptor arrays larger than KMALLOC_MAX_CACHE_SIZE, pass
NUMA_NO_NODE to keep the policy-aware page allocation path. An explicit
node would otherwise lose the MPOL_BIND nodemask on fallback. Select the
policy node only for slab-sized arrays, avoiding an extra advance of an
interleave policy for large allocations.

Moving a pipe's users to another node doesn't migrate its existing
metadata, so migration can still result in remote accesses regardless of
this change. Generic allocations may reuse remote partial slabs, making
initial placement dependent on allocator state. In contrast, preferring
the policy node leverages the workload's placement hint to improve
locality when users remain on the intended node.

Testing has been performed on a dual-socket NVIDIA Vera system, covering
hackbench, pipe transfers, pipe creation and resizing, pipe_bench, and
targeted stress tests.

The primary hackbench reproducer is:

  $ numactl --physcpubind=0-87 --membind=0 \
      hackbench -P -p -g 10 -f 20 -s 100 -l 100000

Results (over 10 measured runs per case):

              avg       stdev
   before     9.811s    0.130s
   after      5.770s    0.058s

Before this change, allocations could reuse remote pipe metadata. With
this change, both pipe objects and descriptor arrays are allocated on
the requested node, improving locality and reducing hackbench runtime by
approximately 41%.

Reported-by: Quan Liu <qualiu@nvidia.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
 fs/pipe.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 4fa69192e6fba..2a8f9e9f70f84 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -24,6 +24,7 @@
 #include <linux/syscalls.h>
 #include <linux/fcntl.h>
 #include <linux/memcontrol.h>
+#include <linux/mempolicy.h>
 #include <linux/watch_queue.h>
 #include <linux/sysctl.h>
 #include <linux/sort.h>
@@ -874,6 +875,16 @@ bool pipe_is_unprivileged_user(void)
 	return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
 }
 
+/* Prefer the policy node over remote partial slabs, retaining fallback. */
+static int pipe_slab_node(void)
+{
+#ifdef CONFIG_NUMA
+	return mempolicy_slab_node();
+#else
+	return NUMA_NO_NODE;
+#endif
+}
+
 struct pipe_inode_info *alloc_pipe_info(void)
 {
 	struct pipe_inode_info *pipe;
@@ -881,8 +892,9 @@ struct pipe_inode_info *alloc_pipe_info(void)
 	struct user_struct *user = get_current_user();
 	unsigned long user_bufs;
 	unsigned int max_size = READ_ONCE(pipe_max_size);
+	int node = pipe_slab_node();
 
-	pipe = kzalloc_obj(struct pipe_inode_info, GFP_KERNEL_ACCOUNT);
+	pipe = kzalloc_node(sizeof(*pipe), GFP_KERNEL_ACCOUNT, node);
 	if (pipe == NULL)
 		goto out_free_uid;
 
@@ -899,8 +911,8 @@ struct pipe_inode_info *alloc_pipe_info(void)
 	if (too_many_pipe_buffers_hard(user_bufs) && pipe_is_unprivileged_user())
 		goto out_revert_acct;
 
-	pipe->bufs = kzalloc_objs(struct pipe_buffer, pipe_bufs,
-				  GFP_KERNEL_ACCOUNT);
+	pipe->bufs = kcalloc_node(pipe_bufs, sizeof(*pipe->bufs),
+				  GFP_KERNEL_ACCOUNT, node);
 
 	if (pipe->bufs) {
 		init_waitqueue_head(&pipe->rd_wait);
@@ -1375,12 +1387,18 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
 {
 	struct pipe_buffer *bufs;
 	unsigned int head, tail, mask, n;
+	int node = NUMA_NO_NODE;
 
 	/* nr_slots larger than limits of pipe->{head,tail} */
 	if (unlikely(nr_slots > (pipe_index_t)-1u))
 		return -EINVAL;
 
-	bufs = kzalloc_objs(*bufs, nr_slots, GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
+	/* Keep the policy nodemask for allocations that bypass slab caches. */
+	if (nr_slots <= KMALLOC_MAX_CACHE_SIZE / sizeof(*bufs))
+		node = pipe_slab_node();
+
+	bufs = kcalloc_node(nr_slots, sizeof(*bufs),
+			    GFP_KERNEL_ACCOUNT | __GFP_NOWARN, node);
 	if (unlikely(!bufs))
 		return -ENOMEM;
 
-- 
2.56.0