Re: [patch 026/158] mm: emit tracepoint when RSS changes

[Steven Rostedt <rostedt@goodmis.org>]

On Sat, 30 Nov 2019 17:50:30 -0800
akpm@linux-foundation.org wrote:

>  /* Optimized variant when page is already known not to be PageAnon */
> --- a/include/trace/events/kmem.h~mm-emit-tracepoint-when-rss-changes
> +++ a/include/trace/events/kmem.h
> @@ -316,6 +316,27 @@ TRACE_EVENT(mm_page_alloc_extfrag,
>  		__entry->change_ownership)
>  );
>  
> +TRACE_EVENT(rss_stat,
> +
> +	TP_PROTO(int member,
> +		long count),
> +
> +	TP_ARGS(member, count),
> +
> +	TP_STRUCT__entry(
> +		__field(int, member)
> +		__field(long, size)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->member = member;
> +		__entry->size = (count << PAGE_SHIFT);

It's best to put all calculations (including shifts) in the print part,
as that's the slow path. The TP_fast_assign() is done when the trace
point is triggered (during the execution of the code). It's best to
keep this in the slow path (TP_printk).

		__entry->count = count;

> +	),
> +
> +	TP_printk("member=%d size=%ldB",
> +		__entry->member,
> +		__entry->size)

		__entry->count << PAGE_SHIFT)

-- Steve


> +	);
>  #endif /* _TRACE_KMEM_H */
>  
>  /* This part must be outside protection */
> --- a/mm/memory.c~mm-emit-tracepoint-when-rss-changes