From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751900AbdJYQ1g (ORCPT ); Wed, 25 Oct 2017 12:27:36 -0400 Received: from mga06.intel.com ([134.134.136.31]:38467 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751775AbdJYQ1f (ORCPT ); Wed, 25 Oct 2017 12:27:35 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.43,432,1503385200"; d="scan'208";a="167500976" From: changbin.du@intel.com To: rostedt@goodmis.org, mingo@redhat.com Cc: linux-kernel@vger.kernel.org, Changbin Du Subject: [PATCH v2] tracing: Allocate mask_str buffer dynamically Date: Thu, 26 Oct 2017 00:20:28 +0800 Message-Id: <1508948428-4969-1-git-send-email-changbin.du@intel.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Changbin Du 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 --- 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