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Message-Id: <1508948428-4969-1-git-send-email-changbin.du@intel.com>
Date: Thu, 26 Oct 2017 00:20:28 +0800
From: changbin.du@...el.com
To: rostedt@...dmis.org, mingo@...hat.com
Cc: linux-kernel@...r.kernel.org, Changbin Du <changbin.du@...el.com>
Subject: [PATCH v2] tracing: Allocate mask_str buffer dynamically
From: Changbin Du <changbin.du@...el.com>
The default NR_CPUS can be very large, but actual possible nr_cpu_ids
usually is very small. For my x86 distribution, the NR_CPUS is 8192 and
nr_cpu_ids is 4. About 2 pages are wasted.
Most machines don't have so many CPUs, so define a array with NR_CPUS
just wastes memory. So let's allocate the buffer dynamically when need.
The exact buffer size should be:
DIV_ROUND_UP(nr_cpu_ids, 4) + nr_cpu_ids/32 + 2;
Example output:
ff,ffffffff
Signed-off-by: Changbin Du <changbin.du@...el.com>
---
v2:
- remove 'static' declaration.
- fix buffer size.
---
kernel/trace/trace.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 752e5da..6b70648 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4184,31 +4184,33 @@ static const struct file_operations show_traces_fops = {
*/
static DEFINE_MUTEX(tracing_cpumask_update_lock);
-/*
- * Temporary storage for the character representation of the
- * CPU bitmask (and one more byte for the newline):
- */
-static char mask_str[NR_CPUS + 1];
-
static ssize_t
tracing_cpumask_read(struct file *filp, char __user *ubuf,
size_t count, loff_t *ppos)
{
struct trace_array *tr = file_inode(filp)->i_private;
+ char *mask_str;
int len;
+ /* Bitmap, ',' and two more bytes for the newline and '\0'. */
+ len = DIV_ROUND_UP(nr_cpu_ids, 4) + nr_cpu_ids/32 + 2;
+ mask_str = kmalloc(len, GFP_KERNEL);
+ if (!mask_str)
+ return -ENOMEM;
+
mutex_lock(&tracing_cpumask_update_lock);
- len = snprintf(mask_str, count, "%*pb\n",
+ len = snprintf(mask_str, len, "%*pb\n",
cpumask_pr_args(tr->tracing_cpumask));
if (len >= count) {
count = -EINVAL;
goto out_err;
}
- count = simple_read_from_buffer(ubuf, count, ppos, mask_str, NR_CPUS+1);
+ count = simple_read_from_buffer(ubuf, count, ppos, mask_str, len);
out_err:
mutex_unlock(&tracing_cpumask_update_lock);
+ kfree(mask_str);
return count;
}
--
2.7.4
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