On Wed, Oct 25, 2017 at 07:24:36PM +0800, changbin...@intel.com wrote:
> From: Changbin Du <changbin...@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.
>
> Signed-off-by: Changbin Du <changbin...@intel.com>
> ---
> kernel/trace/trace.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 752e5da..d1b3f11 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4184,19 +4184,18 @@ 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;
> + static char *mask_str;
ah, need remove 'static'.> int len; > > + mask_str = kmalloc(nr_cpu_ids + 1, GFP_KERNEL); > + if (!mask_str) > + return -ENOMEM; > + > mutex_lock(&tracing_cpumask_update_lock); > > len = snprintf(mask_str, count, "%*pb\n", > @@ -4205,10 +4204,12 @@ tracing_cpumask_read(struct file *filp, char __user > *ubuf, > 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, nr_cpu_ids+1); > > out_err: > mutex_unlock(&tracing_cpumask_update_lock); > + kfree(mask_str); > > return count; > } > -- > 2.7.4 > -- Thanks, Changbin Du
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