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Message-ID: <20240220140703.182330529@goodmis.org>
Date: Tue, 20 Feb 2024 09:06:14 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Vincent Donnefort <vdonnefort@...gle.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Mete Durlu <meted@...ux.ibm.com>
Subject: [PATCH v4 1/3] tracing: Have saved_cmdlines arrays all in one allocation
From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
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@gandalf.local.home/
Fixes: 44dc5c41b5b1 ("tracing: Fix wasted memory in saved_cmdlines logic")
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
Changes since v4: https://lore.kernel.org/linux-trace-kernel/20240216210150.379809261@goodmis.org
- Do not kfree() map_cmdline_to_pid now that it is included in the
page allocations.
kernel/trace/trace.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8198bfc54b58..52faa30e64ed 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2325,6 +2325,10 @@ 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];
@@ -2339,7 +2343,6 @@ 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);
}
@@ -2352,7 +2355,7 @@ 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);
@@ -2364,16 +2367,11 @@ 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,
--
2.43.0
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