Messages in this thread Patch in this message | | | From | changbin.du@intel ... | Subject | [PATCH v2] tracing: Allocate mask_str buffer dynamically | Date | Thu, 26 Oct 2017 00:20:28 +0800 |
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From: Changbin Du <changbin.du@intel.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@intel.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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