Re: [PATCH] mm/zsmalloc: add trace events for zs_compact

Minchan Kim
2016-06-13T04:42:41Z

On Wed, Jun 08, 2016 at 02:39:19PM +0800, Ganesh Mahendran wrote:

<snip>

> zsmalloc is not only used by zram, but also zswap. Maybe
> others in the future.
>
> I tried to use function_graph. It seems there are too much log
> printed:
> ------
> root@leo-test:/sys/kernel/debug/tracing# cat trace
> # tracer: function_graph
> #
> # CPU DURATION FUNCTION CALLS
> # | | | | | | |
> 2) | zs_compact [zsmalloc]() {
> 2) | /* zsmalloc_compact_start: pool zram0 */
> 2) 0.889 us | _raw_spin_lock();
> 2) 0.896 us | isolate_zspage [zsmalloc]();
> 2) 0.938 us | _raw_spin_lock();
> 2) 0.875 us | isolate_zspage [zsmalloc]();
> 2) 0.942 us | _raw_spin_lock();
> 2) 0.962 us | isolate_zspage [zsmalloc]();
> ...
> 2) 0.879 us | insert_zspage [zsmalloc]();
> 2) 4.520 us | }
> 2) 0.975 us | _raw_spin_lock();
> 2) 0.890 us | isolate_zspage [zsmalloc]();
> 2) 0.882 us | _raw_spin_lock();
> 2) 0.894 us | isolate_zspage [zsmalloc]();
> 2) | /* zsmalloc_compact_end: pool zram0: 0 pages
> compacted(total 0) */
> 2) # 1351.241 us | }
> ------
> => 1351.241 us used
>
> And it seems the overhead of function_graph is bigger than trace event.
>
> bash-3682 [002] .... 1439.180646: zsmalloc_compact_start: pool zram0
> bash-3682 [002] .... 1439.180659: zsmalloc_compact_end: pool zram0:
> 0 pages compacted(total 0)
> => 13 us > 1351.241 us

You could use set_ftrace_filter to cut out.

To introduce new event trace to get a elasped time, it's pointless,
I think.

It should have more like pool name you mentioned.
Like saying other thread, It would be better to show
[pool name, compact size_class,
the number of object moved, the number of freed page], IMO.

Thanks.