From: Eric Sandeen <sandeen@sandeen.net>
To: Dave Chinner <david@fromorbit.com>,
Carlos Maiolino <cmaiolino@redhat.com>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 2/2] xfs: use offsetof() in place of offset macros for __xfsstats
Date: Thu, 11 Oct 2018 09:04:14 -0500 [thread overview]
Message-ID: <d81b5be8-23ec-e3c6-9270-fa311848ab38@sandeen.net> (raw)
In-Reply-To: <20181011052957.GO6311@dastard>
On 10/11/18 12:29 AM, Dave Chinner wrote:
> On Wed, Oct 10, 2018 at 02:37:08PM +0200, Carlos Maiolino wrote:
>> Most offset macro mess is used in xfs_stats_format() only, and we can
>> simply get the right offsets using offsetof(), instead of several macros
>> to mark the offsets inside __xfsstats structure.
>>
>> Replace all XFSSTAT_END_* macros by a single helper macro to get the
>> right offset into __xfsstats, and use this helper in xfs_stats_format()
>> directly.
>>
>> The quota stats code, still looks a bit cleaner when using XFSSTAT_*
>> macros, so, this patch also defines XFSSTAT_START_XQMSTAT and
>> XFSSTAT_END_XQMSTAT locally to that code. This also should prevent
>> offset mistakes when updates are done into __xfsstats.
>>
>> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
>> ---
>> fs/xfs/xfs_stats.c | 52 +++++++++++++++++++++++++---------------------
>> fs/xfs/xfs_stats.h | 28 +++----------------------
>> 2 files changed, 31 insertions(+), 49 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_stats.c b/fs/xfs/xfs_stats.c
>> index 740ac9674848..cc509743facd 100644
>> --- a/fs/xfs/xfs_stats.c
>> +++ b/fs/xfs/xfs_stats.c
>> @@ -29,30 +29,30 @@ int xfs_stats_format(struct xfsstats __percpu *stats, char *buf)
>> char *desc;
>> int endpoint;
>> } xstats[] = {
>> - { "extent_alloc", XFSSTAT_END_EXTENT_ALLOC },
>> - { "abt", XFSSTAT_END_ALLOC_BTREE },
>> - { "blk_map", XFSSTAT_END_BLOCK_MAPPING },
>> - { "bmbt", XFSSTAT_END_BLOCK_MAP_BTREE },
>> - { "dir", XFSSTAT_END_DIRECTORY_OPS },
>> - { "trans", XFSSTAT_END_TRANSACTIONS },
>> - { "ig", XFSSTAT_END_INODE_OPS },
>> - { "log", XFSSTAT_END_LOG_OPS },
>> - { "push_ail", XFSSTAT_END_TAIL_PUSHING },
>> - { "xstrat", XFSSTAT_END_WRITE_CONVERT },
>> - { "rw", XFSSTAT_END_READ_WRITE_OPS },
>> - { "attr", XFSSTAT_END_ATTRIBUTE_OPS },
>> - { "icluster", XFSSTAT_END_INODE_CLUSTER },
>> - { "vnodes", XFSSTAT_END_VNODE_OPS },
>> - { "buf", XFSSTAT_END_BUF },
>> - { "abtb2", XFSSTAT_END_ABTB_V2 },
>> - { "abtc2", XFSSTAT_END_ABTC_V2 },
>> - { "bmbt2", XFSSTAT_END_BMBT_V2 },
>> - { "ibt2", XFSSTAT_END_IBT_V2 },
>> - { "fibt2", XFSSTAT_END_FIBT_V2 },
>> - { "rmapbt", XFSSTAT_END_RMAP_V2 },
>> - { "refcntbt", XFSSTAT_END_REFCOUNT },
>> + { "extent_alloc", xfsstats_offset(xs_abt_lookup) },
>> + { "abt", xfsstats_offset(xs_blk_mapr) },
>> + { "blk_map", xfsstats_offset(xs_bmbt_lookup) },
>> + { "bmbt", xfsstats_offset(xs_dir_lookup) },
>> + { "dir", xfsstats_offset(xs_trans_sync) },
>> + { "trans", xfsstats_offset(xs_ig_attempts) },
>> + { "ig", xfsstats_offset(xs_log_writes) },
>> + { "log", xfsstats_offset(xs_try_logspace)},
>> + { "push_ail", xfsstats_offset(xs_xstrat_quick)},
>> + { "xstrat", xfsstats_offset(xs_write_calls) },
>> + { "rw", xfsstats_offset(xs_attr_get) },
>> + { "attr", xfsstats_offset(xs_iflush_count)},
>> + { "icluster", xfsstats_offset(vn_active) },
>> + { "vnodes", xfsstats_offset(xb_get) },
>> + { "buf", xfsstats_offset(xs_abtb_2) },
>> + { "abtb2", xfsstats_offset(xs_abtc_2) },
>> + { "abtc2", xfsstats_offset(xs_bmbt_2) },
>> + { "bmbt2", xfsstats_offset(xs_ibt_2) },
>> + { "ibt2", xfsstats_offset(xs_fibt_2) },
>> + { "fibt2", xfsstats_offset(xs_rmap_2) },
>> + { "rmapbt", xfsstats_offset(xs_refcbt_2) },
>> + { "refcntbt", xfsstats_offset(xs_qm_dqreclaims)},
>> /* we print both series of quota information together */
>> - { "qm", XFSSTAT_END_QM },
>> + { "qm", xfsstats_offset(xs_xstrat_bytes)},
>> };
>
> Now that I look at this more closely , it's a little bit ... odd.
> i.e. the endpoint offset points to the first variable in the next
> line, not the last variable of the stats line described by the text.
> While it works, it just doesn't seem quite right to me.
I had the same thought initially, but talked myself out of it.
And I started to reply here with why, then un-convinced myself again,
and now I'm re-convincing myself. Bear with me. ;)
> Can we change it so that the index in the table is the last variable
> of that line? This may require changing the inner loop to a <= check
> rather than a < check, but the table would make more sense this way.
> ie.
>
> { "extent_alloc", xfsstats_index(xs_freeb) },
> { "abt", xfsstats_index(xs_abt_delrec) },
> .....
First off, any change here would definitely require good comments. :)
So let's remember the the overarching goal here is to make things
more foolproof when the stats structure changes.
struct __xfsstats {
# define XFSSTAT_END_EXTENT_ALLOC 4
uint32_t xs_allocx;
uint32_t xs_allocb;
uint32_t xs_freex;
uint32_t xs_freeb;
# define XFSSTAT_END_ALLOC_BTREE (XFSSTAT_END_EXTENT_ALLOC+4)
uint32_t xs_abt_lookup;
uint32_t xs_abt_compare;
uint32_t xs_abt_insrec;
uint32_t xs_abt_delrec;
...
and "what can go wrong" is somebody extends one of the groups without
changing the end, or they insert a group without changing where the xqm
stats start.
The most foolproof thing would be to define the boundaries at the start
of each group, because adding new stats at the end of the line is allowed,
but would require changing the END macros. i.e. something like:
/*
* XFS global statistics
*/
struct __xfsstats {
# define XFSSTAT_START_EXTENT_ALLOC XFS_STATS_CALC_INDEX(xs_allocx)
uint32_t xs_allocx;
uint32_t xs_allocb;
uint32_t xs_freex;
uint32_t xs_freeb;
# define XFSSTAT_START_ALLOC_BTREE XFS_STATS_CALC_INDEX(xs_abt_lookup)
uint32_t xs_abt_lookup;
...
and these START points would never change.
Then, the printing loop needs to be adjusted to look forward to the next
group to know when to stop, something like this where we change "endpoint"
to "start" and add a NULL guard at the end,
} xstats[] = {
{ "extent_alloc", XFSSTAT_START_EXTENT_ALLOC },
{ "abt", XFSSTAT_START_ALLOC_BTRE },
...
{ "qm", XFSSTAT_START_QM },
{ NULL, XFSSTAT_END },
};
then look ahead while we print:
for (i = j = 0; i < ARRAY_SIZE(xstats) && xstats[i].desc; i++) {
len += snprintf(buf + len, PATH_MAX - len, "%s",
xstats[i].desc);
/* inner loop does each group */
for (; j < xstats[i+1].start; j++)
len += snprintf(buf + len, PATH_MAX - len, " %u",
counter_val(stats, j));
len += snprintf(buf + len, PATH_MAX - len, "\n");
}
testing xstats[i].desc in the outer loop should stop at the last NULL line,
and looking ahead to xstats[i+1].start in the innner loop checks where the
next group will start.
XFSSTAT_END could be defined in terms of ARRAY_SIZE so it's automatic, too.
>
> It may require a different macro for the expanded btree stats (the
> array based ones) because they are defined as an array rather than
> individual variables, but I think that's ok given those already have
> special macros for changing them.
>
>> +#define xfsstats_offset(f) (offsetof(struct __xfsstats, f)/sizeof(uint32_t))
So, another thing worth pointing out is that we already have "this" macro:
/*
* simple wrapper for getting the array index of s struct member offset
*/
#define XFS_STATS_CALC_INDEX(member) \
(offsetof(struct __xfsstats, member) / (int)sizeof(uint32_t))
so probably no need to define it again w/ another name, probably worth
consolidating.
> I also think this should be named xfsstats_index(), not _offset. i.e.
> it's an index into a structure we treat as an array of ints, not a byte
> offset from the start of a u8 buffer....
agreed, see above :D
>> +
>> struct xfsstats {
>> union {
>> struct __xfsstats s;
>> - uint32_t a[XFSSTAT_END_XQMSTAT];
>> + uint32_t a[xfsstats_offset(xs_qm_dquot)];
>
> I think this should remain XFSSTAT_END_XQMSTAT, as we still define
> that and require the quota stats to be at the end of the structure.
>
> Cheers,
>
> Dave.
>
next prev parent reply other threads:[~2018-10-11 21:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-10 12:37 [PATCH 0/2] xfs stats fixes - V2 Carlos Maiolino
2018-10-10 12:37 ` [PATCH 1/2] xfs: Fix xqmstats offsets in /proc/fs/xfs/xqmstat Carlos Maiolino
2018-10-10 12:37 ` [PATCH 2/2] xfs: use offsetof() in place of offset macros for __xfsstats Carlos Maiolino
2018-10-10 14:49 ` Darrick J. Wong
2018-10-10 14:58 ` Carlos Maiolino
2018-10-10 15:02 ` Darrick J. Wong
2018-10-10 21:28 ` Dave Chinner
2018-10-11 5:29 ` Dave Chinner
2018-10-11 14:04 ` Eric Sandeen [this message]
2018-10-12 7:01 ` Dave Chinner
2018-10-12 15:00 ` Eric Sandeen
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