From dd05add7b2b6004c5fa3a1f276f56d8668f86b65 Mon Sep 17 00:00:00 2001 From: Paulo Alcantara Date: Sat, 26 Sep 2026 19:20:30 -0300 Subject: netfs: zero the tail of a short DIO/unbuffered read The buffered read collector zero-fills the tail of a short read that stops below the inode's i_size (netfs_clear_unread()), so a read that races an extending write still returns the expected number of bytes. The non-buffered collector path does no such thing: it just records how much was transferred. Add the same zero-fill for the non-buffered case, gated on NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short result from it is known to be safe to treat as a hole, as opposed to NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of the file and should be reported short as-is. Only CLEAR_TAIL should zero-fill here; a real EOF must stay a real short read. No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest, so this is inert on its own -- a following change teaches cifs to set it in the one case that needs it. Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item") Reviewed-by: David Howells Reviewed-by: Namjae Jeon Signed-off-by: Paulo Alcantara Cc: Christian Brauner Cc: Matthew Wilcox Cc: Ronnie Sahlberg Cc: Shyam Prasad N Cc: Tom Talpey Cc: Bharath SM Cc: stable@vger.kernel.org --- Documentation/admin-guide/numastat.rst | 55 ++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) create mode 100644 Documentation/admin-guide/numastat.rst (limited to 'Documentation/admin-guide/numastat.rst') diff --git a/Documentation/admin-guide/numastat.rst b/Documentation/admin-guide/numastat.rst new file mode 100644 index 000000000..08ec2c2bd --- /dev/null +++ b/Documentation/admin-guide/numastat.rst @@ -0,0 +1,55 @@ +=============================== +Numa policy hit/miss statistics +=============================== + +/sys/devices/system/node/node*/numastat + +All units are pages. Hugepages have separate counters. + +The numa_hit, numa_miss and numa_foreign counters reflect how well processes +are able to allocate memory from nodes they prefer. If they succeed, numa_hit +is incremented on the preferred node, otherwise numa_foreign is incremented on +the preferred node and numa_miss on the node where allocation succeeded. + +Usually preferred node is the one local to the CPU where the process executes, +but restrictions such as mempolicies can change that, so there are also two +counters based on CPU local node. local_node is similar to numa_hit and is +incremented on allocation from a node by CPU on the same node. other_node is +similar to numa_miss and is incremented on the node where allocation succeeds +from a CPU from a different node. Note there is no counter analogical to +numa_foreign. + +In more detail: + +=============== ============================================================ +numa_hit A process wanted to allocate memory from this node, + and succeeded. + +numa_miss A process wanted to allocate memory from another node, + but ended up with memory from this node. + +numa_foreign A process wanted to allocate on this node, + but ended up with memory from another node. + +local_node A process ran on this node's CPU, + and got memory from this node. + +other_node A process ran on a different node's CPU + and got memory from this node. + +interleave_hit Interleaving wanted to allocate from this node + and succeeded. +=============== ============================================================ + +For easier reading you can use the numastat utility from the numactl package +(http://oss.sgi.com/projects/libnuma/). Note that it only works +well right now on machines with a small number of CPUs. + +Note that on systems with memoryless nodes (where a node has CPUs but no +memory) the numa_hit, numa_miss and numa_foreign statistics can be skewed +heavily. In the current kernel implementation, if a process prefers a +memoryless node (i.e. because it is running on one of its local CPU), the +implementation actually treats one of the nearest nodes with memory as the +preferred node. As a result, such allocation will not increase the numa_foreign +counter on the memoryless node, and will skew the numa_hit, numa_miss and +numa_foreign statistics of the nearest node. -- cgit v1.3.1