linux-kernel - Re: [RFC PATCH 4/4] [PATCH 4/4] mm: add tracing for VMA merges

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Date:   Fri, 18 Feb 2022 13:09:20 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jakub Matěna <matenajakub@...il.com>
Cc:     linux-mm@...ck.org, patches@...ts.linux.dev,
        linux-kernel@...r.kernel.org, vbabka@...e.cz, mhocko@...nel.org,
        mgorman@...hsingularity.net, willy@...radead.org,
        liam.howlett@...cle.com, hughd@...gle.com, kirill@...temov.name,
        riel@...riel.com, peterz@...radead.org
Subject: Re: [RFC PATCH 4/4] [PATCH 4/4] mm: add tracing for VMA merges

On Fri, 18 Feb 2022 13:20:19 +0100
Jakub Matěna <matenajakub@...il.com> wrote:

> diff --git a/include/trace/events/mmap.h b/include/trace/events/mmap.h
> index 4661f7ba07c0..9f6439e2ed2d 100644
> --- a/include/trace/events/mmap.h
> +++ b/include/trace/events/mmap.h
> @@ -6,6 +6,7 @@
>  #define _TRACE_MMAP_H
>  
>  #include <linux/tracepoint.h>
> +#include <../mm/internal.h>
>  
>  TRACE_EVENT(vm_unmapped_area,
>  
> @@ -42,6 +43,60 @@ TRACE_EVENT(vm_unmapped_area,
>  		__entry->low_limit, __entry->high_limit, __entry->align_mask,
>  		__entry->align_offset)
>  );
> +
> +TRACE_EVENT(vm_av_merge,
> +
> +	TP_PROTO(int merged, enum vma_merge_res merge_prev, enum vma_merge_res merge_next, enum vma_merge_res merge_both),
> +
> +	TP_ARGS(merged, merge_prev, merge_next, merge_both),
> +
> +	TP_STRUCT__entry(
> +		__field(int,			merged)
> +		__field(enum vma_merge_res,	predecessor_different_av)
> +		__field(enum vma_merge_res,	successor_different_av)
> +		__field(enum vma_merge_res,	predecessor_with_successor_different_av)
> +		__field(int,			diff_count)
> +		__field(int,			failed_count)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->merged = merged == 0;
> +		__entry->predecessor_different_av = merge_prev;
> +		__entry->successor_different_av = merge_next;
> +		__entry->predecessor_with_successor_different_av = merge_both;
> +		__entry->diff_count = (merge_prev == AV_MERGE_DIFFERENT)
> +		+ (merge_next == AV_MERGE_DIFFERENT) + (merge_both == AV_MERGE_DIFFERENT);
> +		__entry->failed_count = (merge_prev == AV_MERGE_FAILED)
> +		+ (merge_next == AV_MERGE_FAILED) + (merge_both == AV_MERGE_FAILED);

Please indent the above better. That is:

		__entry->diff_count = (merge_prev == AV_MERGE_DIFFERENT)
				+ (merge_next == AV_MERGE_DIFFERENT)
				+ (merge_both == AV_MERGE_DIFFERENT);


> +	),
> +
> +	TP_printk("merged=%d predecessor=%d successor=%d predecessor_with_successor=%d diff_count=%d failed_count=%d\n",
> +		__entry->merged,
> +		__entry->predecessor_different_av, __entry->successor_different_av,
> +		__entry->predecessor_with_successor_different_av,
> +		__entry->diff_count, __entry->failed_count)

To make the above easier to read for humans, you could have at the start:

#define AV_MERGE_TYPES		\
	EM(MERGE_FAILED),	\
	EM(AV_MERGE_FAILED)	\
	EM(MERGE_OK)		\
	EMe(AV_MERGE_DIFFERENT)

#define EM(a)	TRACE_DEFINE_ENUM(a);
#define EMe(a)	TRACE_DEFINE_ENUM(a);

AV_MERGE_TYPES

#undef EM
#undef EMe

#define EM(a) 	{a, #a},
#define EMe(a)	{a, #a}

Then:

	TP_printk("merged=%d predecessor=%s successor=%s predecessor_with_successor=%s diff_count=%d failed_count=%d",

(note, no "\n", get rid of that)

		__entry->merged,
		__print_symbolic(predecessor_different_av, AV_MERGE_TYPES),
		__print_symbolic(successor_different_av, AV_MERGE_TYPES),
		__print_symbolic(predecessor_with_successor_different_av, AV_MERGE_TYPES),
		__entry->diff_count, __entry->failed_count)

Then the output will show strings instead of meaningless numbers.

-- Steve


> +
> +);
> +
> +TRACE_EVENT(vm_pgoff_merge,
> +
> +	TP_PROTO(struct vm_area_struct *vma, bool anon_pgoff_updated),
> +
> +	TP_ARGS(vma, anon_pgoff_updated),
> +
> +	TP_STRUCT__entry(
> +		__field(bool,	faulted)
> +		__field(bool,	updated)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->faulted = vma->anon_vma;
> +		__entry->updated = anon_pgoff_updated;
> +	),
> +
> +	TP_printk("faulted=%d updated=%d\n",
> +		__entry->faulted, __entry->updated)
> +);
>  #endif
>  
>  /* This part must be outside protection */