This is a note to let you know that I've just added the patch titled
tracing: Have saved_cmdlines arrays all in one allocation
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracing-have-saved_cmdlines-arrays-all-in-one-alloca.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 6efaa60f01e9509b14692fe3c53902eb8e410880
Author: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Date: Tue Feb 20 09:06:14 2024 -0500
tracing: Have saved_cmdlines arrays all in one allocation
[ Upstream commit 0b18c852cc6fb8284ac0ab97e3e840974a6a8a64 ]
The saved_cmdlines have three arrays for mapping PIDs to COMMs:
- map_pid_to_cmdline[]
- map_cmdline_to_pid[]
- saved_cmdlines
The map_pid_to_cmdline[] is PID_MAX_DEFAULT in size and holds the index
into the other arrays. The map_cmdline_to_pid[] is a mapping back to the
full pid as it can be larger than PID_MAX_DEFAULT. And the
saved_cmdlines[] just holds the COMMs associated to the pids.
Currently the map_pid_to_cmdline[] and saved_cmdlines[] are allocated
together (in reality the saved_cmdlines is just in the memory of the
rounding of the allocation of the structure as it is always allocated in
powers of two). The map_cmdline_to_pid[] array is allocated separately.
Since the rounding to a power of two is rather large (it allows for 8000
elements in saved_cmdlines), also include the map_cmdline_to_pid[] array.
(This drops it to 6000 by default, which is still plenty for most use
cases). This saves even more memory as the map_cmdline_to_pid[] array
doesn't need to be allocated.
Link: https://lore.kernel.org/linux-trace-kernel/20240212174011.068211d9@xxxxxxxxxxxxxxxxxx/
Link: https://lore.kernel.org/linux-trace-kernel/20240220140703.182330529@xxxxxxxxxxx
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Vincent Donnefort <vdonnefort@xxxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
Cc: Mete Durlu <meted@xxxxxxxxxxxxx>
Fixes: 44dc5c41b5b1 ("tracing: Fix wasted memory in saved_cmdlines logic")
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b16291f4c5731..9f5b9036f001d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2244,6 +2244,10 @@ struct saved_cmdlines_buffer {
};
static struct saved_cmdlines_buffer *savedcmd;
+/* Holds the size of a cmdline and pid element */
+#define SAVED_CMDLINE_MAP_ELEMENT_SIZE(s) \
+ (TASK_COMM_LEN + sizeof((s)->map_cmdline_to_pid[0]))
+
static inline char *get_saved_cmdlines(int idx)
{
return &savedcmd->saved_cmdlines[idx * TASK_COMM_LEN];
@@ -2258,7 +2262,6 @@ static void free_saved_cmdlines_buffer(struct saved_cmdlines_buffer *s)
{
int order = get_order(sizeof(*s) + s->cmdline_num * TASK_COMM_LEN);
- kfree(s->map_cmdline_to_pid);
kmemleak_free(s);
free_pages((unsigned long)s, order);
}
@@ -2271,7 +2274,7 @@ static struct saved_cmdlines_buffer *allocate_cmdlines_buffer(unsigned int val)
int order;
/* Figure out how much is needed to hold the given number of cmdlines */
- orig_size = sizeof(*s) + val * TASK_COMM_LEN;
+ orig_size = sizeof(*s) + val * SAVED_CMDLINE_MAP_ELEMENT_SIZE(s);
order = get_order(orig_size);
size = 1 << (order + PAGE_SHIFT);
page = alloc_pages(GFP_KERNEL, order);
@@ -2283,16 +2286,11 @@ static struct saved_cmdlines_buffer *allocate_cmdlines_buffer(unsigned int val)
memset(s, 0, sizeof(*s));
/* Round up to actual allocation */
- val = (size - sizeof(*s)) / TASK_COMM_LEN;
+ val = (size - sizeof(*s)) / SAVED_CMDLINE_MAP_ELEMENT_SIZE(s);
s->cmdline_num = val;
- s->map_cmdline_to_pid = kmalloc_array(val,
- sizeof(*s->map_cmdline_to_pid),
- GFP_KERNEL);
- if (!s->map_cmdline_to_pid) {
- free_saved_cmdlines_buffer(s);
- return NULL;
- }
+ /* Place map_cmdline_to_pid array right after saved_cmdlines */
+ s->map_cmdline_to_pid = (unsigned *)&s->saved_cmdlines[val * TASK_COMM_LEN];
s->cmdline_idx = 0;
memset(&s->map_pid_to_cmdline, NO_CMDLINE_MAP,
