* [PATCH v2] tracing: Allocate mask_str buffer dynamically
@ 2017-10-25 16:20 changbin.du
2017-10-26 11:15 ` Steven Rostedt
2017-10-31 16:19 ` Steven Rostedt
0 siblings, 2 replies; 4+ messages in thread
From: changbin.du @ 2017-10-25 16:20 UTC (permalink / raw)
To: rostedt, mingo; +Cc: linux-kernel, Changbin Du
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);
-/*
- * 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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] tracing: Allocate mask_str buffer dynamically
2017-10-25 16:20 [PATCH v2] tracing: Allocate mask_str buffer dynamically changbin.du
@ 2017-10-26 11:15 ` Steven Rostedt
2017-10-31 16:19 ` Steven Rostedt
1 sibling, 0 replies; 4+ messages in thread
From: Steven Rostedt @ 2017-10-26 11:15 UTC (permalink / raw)
To: changbin.du; +Cc: mingo, linux-kernel
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>
>
Thanks for sending this. I'm currently traveling for conferences, and
may miss looking at this when I get back. Please send me a friendly
ping reply to this email next week, if you don't hear from me sooner.
-- Steve
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] tracing: Allocate mask_str buffer dynamically
2017-10-25 16:20 [PATCH v2] tracing: Allocate mask_str buffer dynamically changbin.du
2017-10-26 11:15 ` Steven Rostedt
@ 2017-10-31 16:19 ` Steven Rostedt
2017-11-01 2:56 ` Du, Changbin
1 sibling, 1 reply; 4+ messages in thread
From: Steven Rostedt @ 2017-10-31 16:19 UTC (permalink / raw)
To: changbin.du; +Cc: mingo, linux-kernel
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;
> }
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] tracing: Allocate mask_str buffer dynamically
2017-10-31 16:19 ` Steven Rostedt
@ 2017-11-01 2:56 ` Du, Changbin
0 siblings, 0 replies; 4+ messages in thread
From: Du, Changbin @ 2017-11-01 2:56 UTC (permalink / raw)
To: Steven Rostedt; +Cc: changbin.du, mingo, linux-kernel
[-- Attachment #1: Type: text/plain, Size: 2776 bytes --]
Hi Rostedt,
On Tue, Oct 31, 2017 at 12:19:58PM -0400, Steven Rostedt wrote:
> 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
>
ok, let me remove it in v3.
> >
> > - 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;
> > }
>
--
Thanks,
Changbin Du
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2017-10-25 16:20 [PATCH v2] tracing: Allocate mask_str buffer dynamically changbin.du
2017-10-26 11:15 ` Steven Rostedt
2017-10-31 16:19 ` Steven Rostedt
2017-11-01 2:56 ` Du, Changbin
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