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Date:   Thu, 14 Nov 2019 07:52:27 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Dmitry Monakhov <dmonakhov@...il.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH 2/2] ext4: Fix extent_status trace events

On Thu, Nov 14, 2019 at 07:03:30AM +0000, Dmitry Monakhov wrote:
>  - show pblock only if it has meaningful value
>  - Add missed EXTENT_STATUS_REFERENCED decoder
>  - Define status flags as explicit numbers instead of implicit enum ones
> 
> # before
>    ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [1/4294967294) 576460752303423487 0x8
>    ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [2/4294967293) 576460752303423487 0x18
>    ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [3/4294967292) 576460752303423487 0x18
>    ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [4/4294967291) 576460752303423487 0x18
> # after
>    ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [1/4294967294) 0 H
>    ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [2/4294967293) 0 HR
>    ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [3/4294967292) 0 HR
>    ext4:ext4_es_lookup_extent_exit: dev 253,0 ino 12 found 1 [4/4294967291) 0 HR
> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@...il.com>
> ---
>  fs/ext4/extents_status.h    | 21 +++++++++++++--------
>  include/trace/events/ext4.h | 11 ++++++-----
>  2 files changed, 19 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/ext4/extents_status.h b/fs/ext4/extents_status.h
> index 131a8b7..64b8fd1 100644
> --- a/fs/ext4/extents_status.h
> +++ b/fs/ext4/extents_status.h
> @@ -30,14 +30,13 @@
>  /*
>   * These flags live in the high bits of extent_status.es_pblk
>   */
> -enum {
> -	ES_WRITTEN_B,
> -	ES_UNWRITTEN_B,
> -	ES_DELAYED_B,
> -	ES_HOLE_B,
> -	ES_REFERENCED_B,
> -	ES_FLAGS

Put:

TRACE_DEFINE_ENUM(ES_WRITTEN_B)
...
TRACE_DEFINE_ENUM(ES_FLAGS)

in include/trace/events/ext4.h and they should work properly.

We found this out the hard way in xfs land by stumbling across the
"documentation" in samples/trace_events/trace_events.h.

(I don't know if that same trick works for the BH flags in the previous
patch.)

--D

> -};
> +
> +#define ES_WRITTEN_B     0
> +#define ES_UNWRITTEN_B   1
> +#define ES_DELAYED_B     2
> +#define ES_HOLE_B        3
> +#define ES_REFERENCED_B  4
> +#define ES_FLAGS         5
>  
>  #define ES_SHIFT (sizeof(ext4_fsblk_t)*8 - ES_FLAGS)
>  #define ES_MASK (~((ext4_fsblk_t)0) << ES_SHIFT)
> @@ -208,6 +207,12 @@ static inline ext4_fsblk_t ext4_es_pblock(struct extent_status *es)
>  	return es->es_pblk & ~ES_MASK;
>  }
>  
> +static inline ext4_fsblk_t ext4_es_show_pblock(struct extent_status *es)
> +{
> +	ext4_fsblk_t pblock = ext4_es_pblock(es);
> +	return pblock == ~ES_MASK ? 0 : pblock;
> +}
> +
>  static inline void ext4_es_store_pblock(struct extent_status *es,
>  					ext4_fsblk_t pb)
>  {
> diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
> index d68e9e5..bdb5fc4 100644
> --- a/include/trace/events/ext4.h
> +++ b/include/trace/events/ext4.h
> @@ -66,7 +66,8 @@ struct partial_cluster;
>  	{ EXTENT_STATUS_WRITTEN,	"W" },			\
>  	{ EXTENT_STATUS_UNWRITTEN,	"U" },			\
>  	{ EXTENT_STATUS_DELAYED,	"D" },			\
> -	{ EXTENT_STATUS_HOLE,		"H" })
> +	{ EXTENT_STATUS_HOLE,		"H" },			\
> +	{ EXTENT_STATUS_REFERENCED,	"R" })
>  
>  #define show_falloc_mode(mode) __print_flags(mode, "|",		\
>  	{ FALLOC_FL_KEEP_SIZE,		"KEEP_SIZE"},		\
> @@ -2262,7 +2263,7 @@ DECLARE_EVENT_CLASS(ext4__es_extent,
>  		__entry->ino	= inode->i_ino;
>  		__entry->lblk	= es->es_lblk;
>  		__entry->len	= es->es_len;
> -		__entry->pblk	= ext4_es_pblock(es);
> +		__entry->pblk	= ext4_es_show_pblock(es);
>  		__entry->status	= ext4_es_status(es);
>  	),
>  
> @@ -2351,7 +2352,7 @@ TRACE_EVENT(ext4_es_find_extent_range_exit,
>  		__entry->ino	= inode->i_ino;
>  		__entry->lblk	= es->es_lblk;
>  		__entry->len	= es->es_len;
> -		__entry->pblk	= ext4_es_pblock(es);
> +		__entry->pblk	= ext4_es_show_pblock(es);
>  		__entry->status	= ext4_es_status(es);
>  	),
>  
> @@ -2405,7 +2406,7 @@ TRACE_EVENT(ext4_es_lookup_extent_exit,
>  		__entry->ino	= inode->i_ino;
>  		__entry->lblk	= es->es_lblk;
>  		__entry->len	= es->es_len;
> -		__entry->pblk	= ext4_es_pblock(es);
> +		__entry->pblk	= ext4_es_show_pblock(es);
>  		__entry->status	= ext4_es_status(es);
>  		__entry->found	= found;
>  	),
> @@ -2573,7 +2574,7 @@ TRACE_EVENT(ext4_es_insert_delayed_block,
>  		__entry->ino		= inode->i_ino;
>  		__entry->lblk		= es->es_lblk;
>  		__entry->len		= es->es_len;
> -		__entry->pblk		= ext4_es_pblock(es);
> +		__entry->pblk		= ext4_es_show_pblock(es);
>  		__entry->status		= ext4_es_status(es);
>  		__entry->allocated	= allocated;
>  	),
> -- 
> 2.7.4
> 

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