Messages in this thread | | | Date | Tue, 31 Oct 2017 12:19:58 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v2] tracing: Allocate mask_str buffer dynamically |
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On Thu, 26 Oct 2017 00:20:28 +0800 changbin.du@intel.com wrote:
> 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);
The above mutex was used to protect mask_str.
> > -/* > - * 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);
This patch can remove the mutex as well, since there's no sharing of the mask anymore.
-- Steve
> > - 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; > }
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