From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753446AbdK3Dra (ORCPT ); Wed, 29 Nov 2017 22:47:30 -0500 Received: from mga09.intel.com ([134.134.136.24]:42400 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751959AbdK3Dr3 (ORCPT ); Wed, 29 Nov 2017 22:47:29 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.45,339,1508828400"; d="scan'208";a="182230401" From: changbin.du@intel.com To: rostedt@goodmis.org Cc: mingo@redhat.com, linux-kernel@vger.kernel.org, Changbin Du Subject: [PATCH v4] tracing: Allocate mask_str buffer dynamically Date: Thu, 30 Nov 2017 11:39:43 +0800 Message-Id: <1512013183-19107-1-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. With this change, the mutext tracing_cpumask_update_lock also can be removed now, which was used to protect mask_str. Signed-off-by: Changbin Du Cc: Steven Rostedt --- v4: - calculate the buffer size using snprintf. (Rostedt) v3: - remove tracing_cpumask_update_lock which was used to protect mask_str. (Rostedt) v2: - remove 'static' declaration. - fix buffer size. --- kernel/trace/trace.c | 29 +++++++++-------------------- 1 file changed, 9 insertions(+), 20 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 73e67b6..53d29c7 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -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; -- 2.7.4