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tracing: Allocate mask_str buffer dynamically

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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.

With this change, the mutext tracing_cpumask_update_lock also can be
removed now, which was used to protect mask_str.

Link: http://lkml.kernel.org/r/1512013183-19107-1-git-send-email-changbin.du@intel.com

Fixes: 36dfe9252b ("ftrace: make use of tracing_cpumask")
Cc: stable@vger.kernel.org
Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Changbin Du 2017-11-30 11:39:43 +08:00 committed by Steven Rostedt (VMware)
parent 250d0c7754
commit 90e406f96f
1 changed files with 9 additions and 20 deletions
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29
kernel/trace/trace.c
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@ -4178,37 +4178,30 @@ static const struct file_operations show_traces_fops = {
.llseek = seq_lseek,
};
/*
* The tracer itself will not take this lock, but still we want
* to provide a consistent cpumask to user-space:
*/
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;
mutex_lock(&tracing_cpumask_update_lock);
len = snprintf(NULL, 0, "%*pb\n",
cpumask_pr_args(tr->tracing_cpumask)) + 1;
mask_str = kmalloc(len, GFP_KERNEL);
if (!mask_str)
return -ENOMEM;
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;
}
@ -4228,8 +4221,6 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf,
if (err)
goto err_unlock;
mutex_lock(&tracing_cpumask_update_lock);
local_irq_disable();
arch_spin_lock(&tr->max_lock);
for_each_tracing_cpu(cpu) {
@ -4252,8 +4243,6 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf,
local_irq_enable();
cpumask_copy(tr->tracing_cpumask, tracing_cpumask_new);
mutex_unlock(&tracing_cpumask_update_lock);
free_cpumask_var(tracing_cpumask_new);
return count;