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    SubjectRe: [PATCH] mm/zsmalloc: add trace events for zs_compact
    Hi, Minchan:

    2016-06-08 13:13 GMT+08:00 Minchan Kim <minchan@kernel.org>:
    > On Wed, Jun 08, 2016 at 09:48:30AM +0800, Ganesh Mahendran wrote:
    >> Hi, Minchan:
    >>
    >> 2016-06-08 8:16 GMT+08:00 Minchan Kim <minchan@kernel.org>:
    >> > Hello Ganesh,
    >> >
    >> > On Tue, Jun 07, 2016 at 04:56:44PM +0800, Ganesh Mahendran wrote:
    >> >> Currently zsmalloc is widely used in android device.
    >> >> Sometimes, we want to see how frequently zs_compact is
    >> >> triggered or how may pages freed by zs_compact(), or which
    >> >> zsmalloc pool is compacted.
    >> >>
    >> >> Most of the time, user can get the brief information from
    >> >> trace_mm_shrink_slab_[start | end], but in some senario,
    >> >> they do not use zsmalloc shrinker, but trigger compaction manually.
    >> >> So add some trace events in zs_compact is convenient. Also we
    >> >> can add some zsmalloc specific information(pool name, total compact
    >> >> pages, etc) in zsmalloc trace.
    >> >
    >> > Sorry, I cannot understand what's the problem now and what you want to
    >> > solve. Could you elaborate it a bit?
    >> >
    >> > Thanks.
    >>
    >> We have backported the zs_compact() to our product(kernel 3.18).
    >> It is usefull for a longtime running device.
    >> But there is not a convenient way to get the detailed information
    >> of zs_comapct() which is usefull for performance optimization.
    >> Information about how much time zs_compact used, which pool is
    >> compacted, how many page freed, etc.
    >
    > You can know how many pages are freed by object compaction via mm_stat
    > each /sys/block/zram-id/mm_stat. And you can use function_graph to know
    > how much time zs_compact used.

    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

    Thanks.

    >
    >
    >> With these information, we will know what is going on in zs_comapct.
    >> And draw the relation between free mem and zs_comapct.
    >>
    >> >
    >> >>
    >> >> This patch add two trace events for zs_compact(), below the trace log:
    >> >> -----------------------------
    >> >> root@land:/ # cat /d/tracing/trace
    >> >> kswapd0-125 [007] ...1 174.176979: zsmalloc_compact_start: pool zram0
    >> >> kswapd0-125 [007] ...1 174.181967: zsmalloc_compact_end: pool zram0: 608 pages compacted(total 1794)
    >> >> kswapd0-125 [000] ...1 184.134475: zsmalloc_compact_start: pool zram0
    >> >> kswapd0-125 [000] ...1 184.135010: zsmalloc_compact_end: pool zram0: 62 pages compacted(total 1856)
    >> >> kswapd0-125 [003] ...1 226.927221: zsmalloc_compact_start: pool zram0
    >> >> kswapd0-125 [003] ...1 226.928575: zsmalloc_compact_end: pool zram0: 250 pages compacted(total 2106)
    >> >> -----------------------------
    >> >>
    >> >> Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
    >> >> ---
    >> >> include/trace/events/zsmalloc.h | 56 +++++++++++++++++++++++++++++++++++++++++
    >> >> mm/zsmalloc.c | 10 ++++++++
    >> >> 2 files changed, 66 insertions(+)
    >> >> create mode 100644 include/trace/events/zsmalloc.h
    >> >>
    >> >> diff --git a/include/trace/events/zsmalloc.h b/include/trace/events/zsmalloc.h
    >> >> new file mode 100644
    >> >> index 0000000..3b6f14e
    >> >> --- /dev/null
    >> >> +++ b/include/trace/events/zsmalloc.h
    >> >> @@ -0,0 +1,56 @@
    >> >> +#undef TRACE_SYSTEM
    >> >> +#define TRACE_SYSTEM zsmalloc
    >> >> +
    >> >> +#if !defined(_TRACE_ZSMALLOC_H) || defined(TRACE_HEADER_MULTI_READ)
    >> >> +#define _TRACE_ZSMALLOC_H
    >> >> +
    >> >> +#include <linux/types.h>
    >> >> +#include <linux/tracepoint.h>
    >> >> +
    >> >> +TRACE_EVENT(zsmalloc_compact_start,
    >> >> +
    >> >> + TP_PROTO(const char *pool_name),
    >> >> +
    >> >> + TP_ARGS(pool_name),
    >> >> +
    >> >> + TP_STRUCT__entry(
    >> >> + __field(const char *, pool_name)
    >> >> + ),
    >> >> +
    >> >> + TP_fast_assign(
    >> >> + __entry->pool_name = pool_name;
    >> >> + ),
    >> >> +
    >> >> + TP_printk("pool %s",
    >> >> + __entry->pool_name)
    >> >> +);
    >> >> +
    >> >> +TRACE_EVENT(zsmalloc_compact_end,
    >> >> +
    >> >> + TP_PROTO(const char *pool_name, unsigned long pages_compacted,
    >> >> + unsigned long pages_total_compacted),
    >> >> +
    >> >> + TP_ARGS(pool_name, pages_compacted, pages_total_compacted),
    >> >> +
    >> >> + TP_STRUCT__entry(
    >> >> + __field(const char *, pool_name)
    >> >> + __field(unsigned long, pages_compacted)
    >> >> + __field(unsigned long, pages_total_compacted)
    >> >> + ),
    >> >> +
    >> >> + TP_fast_assign(
    >> >> + __entry->pool_name = pool_name;
    >> >> + __entry->pages_compacted = pages_compacted;
    >> >> + __entry->pages_total_compacted = pages_total_compacted;
    >> >> + ),
    >> >> +
    >> >> + TP_printk("pool %s: %ld pages compacted(total %ld)",
    >> >> + __entry->pool_name,
    >> >> + __entry->pages_compacted,
    >> >> + __entry->pages_total_compacted)
    >> >> +);
    >> >> +
    >> >> +#endif /* _TRACE_ZSMALLOC_H */
    >> >> +
    >> >> +/* This part must be outside protection */
    >> >> +#include <trace/define_trace.h>
    >> >> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
    >> >> index 213d0e1..441b9f7 100644
    >> >> --- a/mm/zsmalloc.c
    >> >> +++ b/mm/zsmalloc.c
    >> >> @@ -30,6 +30,8 @@
    >> >>
    >> >> #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
    >> >>
    >> >> +#define CREATE_TRACE_POINTS
    >> >> +
    >> >> #include <linux/module.h>
    >> >> #include <linux/kernel.h>
    >> >> #include <linux/sched.h>
    >> >> @@ -52,6 +54,7 @@
    >> >> #include <linux/mount.h>
    >> >> #include <linux/compaction.h>
    >> >> #include <linux/pagemap.h>
    >> >> +#include <trace/events/zsmalloc.h>
    >> >>
    >> >> #define ZSPAGE_MAGIC 0x58
    >> >>
    >> >> @@ -2330,6 +2333,9 @@ unsigned long zs_compact(struct zs_pool *pool)
    >> >> {
    >> >> int i;
    >> >> struct size_class *class;
    >> >> + unsigned long pages_compacted_before = pool->stats.pages_compacted;
    >> >> +
    >> >> + trace_zsmalloc_compact_start(pool->name);
    >> >>
    >> >> for (i = zs_size_classes - 1; i >= 0; i--) {
    >> >> class = pool->size_class[i];
    >> >> @@ -2340,6 +2346,10 @@ unsigned long zs_compact(struct zs_pool *pool)
    >> >> __zs_compact(pool, class);
    >> >> }
    >> >>
    >> >> + trace_zsmalloc_compact_end(pool->name,
    >> >> + pool->stats.pages_compacted - pages_compacted_before,
    >> >> + pool->stats.pages_compacted);
    >> >> +
    >> >> return pool->stats.pages_compacted;
    >> >> }
    >> >> EXPORT_SYMBOL_GPL(zs_compact);
    >> >> --
    >> >> 1.9.1
    >> >>

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