linux-kernel - Re: [PATCH v6 09/14] mm/damon: Add a tracepoint for result writing

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Date:   Tue, 10 Mar 2020 09:03:31 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     SeongJae Park <sjpark@...zon.com>
CC:     <akpm@...ux-foundation.org>, SeongJae Park <sjpark@...zon.de>,
        <aarcange@...hat.com>, <yang.shi@...ux.alibaba.com>,
        <acme@...nel.org>, <alexander.shishkin@...ux.intel.com>,
        <amit@...nel.org>, <brendan.d.gregg@...il.com>,
        <brendanhiggins@...gle.com>, <cai@....pw>,
        <colin.king@...onical.com>, <corbet@....net>, <dwmw@...zon.com>,
        <jolsa@...hat.com>, <kirill@...temov.name>, <mark.rutland@....com>,
        <mgorman@...e.de>, <minchan@...nel.org>, <mingo@...hat.com>,
        <namhyung@...nel.org>, <peterz@...radead.org>,
        <rdunlap@...radead.org>, <rientjes@...gle.com>,
        <rostedt@...dmis.org>, <shuah@...nel.org>, <sj38.park@...il.com>,
        <vbabka@...e.cz>, <vdavydov.dev@...il.com>, <linux-mm@...ck.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 09/14] mm/damon: Add a tracepoint for result writing

On Mon, 24 Feb 2020 13:30:42 +0100
SeongJae Park <sjpark@...zon.com> wrote:

> From: SeongJae Park <sjpark@...zon.de>
> 
> This commit adds a tracepoint for DAMON's result buffer writing.  It is
> called for each writing of the DAMON results and print the result data.
> Therefore, it would be used to easily integrated with other tracepoint
> supporting tracers such as perf.
> 
> Signed-off-by: SeongJae Park <sjpark@...zon.de>

I'm curious, why at the flush of rbuf rather than using a more structured trace
point for each of the writes into rbuf?

Seems it would make more sense to have a tracepoint for each record write out.
Probably at the level of each task, though might be more elegant to do it at the
level of each region within a task and duplicate the header stuff.

> ---
>  include/trace/events/damon.h | 32 ++++++++++++++++++++++++++++++++
>  mm/damon.c                   |  4 ++++
>  2 files changed, 36 insertions(+)
>  create mode 100644 include/trace/events/damon.h
> 
> diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
> new file mode 100644
> index 000000000000..fb33993620ce
> --- /dev/null
> +++ b/include/trace/events/damon.h
> @@ -0,0 +1,32 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM damon
> +
> +#if !defined(_TRACE_DAMON_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_DAMON_H
> +
> +#include <linux/types.h>
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT(damon_write_rbuf,
> +
> +	TP_PROTO(void *buf, const ssize_t sz),
> +
> +	TP_ARGS(buf, sz),
> +
> +	TP_STRUCT__entry(
> +		__dynamic_array(char, buf, sz)
> +	),
> +
> +	TP_fast_assign(
> +		memcpy(__get_dynamic_array(buf), buf, sz);
> +	),
> +
> +	TP_printk("dat=%s", __print_hex(__get_dynamic_array(buf),
> +			__get_dynamic_array_len(buf)))
> +);
> +
> +#endif /* _TRACE_DAMON_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
> diff --git a/mm/damon.c b/mm/damon.c
> index facb1d7f121b..8faf3879f99e 100644
> --- a/mm/damon.c
> +++ b/mm/damon.c
> @@ -9,6 +9,8 @@
>  
>  #define pr_fmt(fmt) "damon: " fmt
>  
> +#define CREATE_TRACE_POINTS
> +
>  #include <linux/damon.h>
>  #include <linux/debugfs.h>
>  #include <linux/delay.h>
> @@ -20,6 +22,7 @@
>  #include <linux/sched/mm.h>
>  #include <linux/sched/task.h>
>  #include <linux/slab.h>
> +#include <trace/events/damon.h>
>  
>  #define damon_get_task_struct(t) \
>  	(get_pid_task(find_vpid(t->pid), PIDTYPE_PID))
> @@ -553,6 +556,7 @@ static void damon_flush_rbuffer(struct damon_ctx *ctx)
>   */
>  static void damon_write_rbuf(struct damon_ctx *ctx, void *data, ssize_t size)
>  {
> +	trace_damon_write_rbuf(data, size);
>  	if (!ctx->rbuf_len || !ctx->rbuf)
>  		return;
>  	if (ctx->rbuf_offset + size > ctx->rbuf_len)