Re: [PATCH] [RFC] xfs: make xfs btree stats less huge

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, xfs@oss.sgi.com
Subject: Re: [PATCH] [RFC] xfs: make xfs btree stats less huge
Date: Mon, 19 Sep 2016 23:10:42 -0700	[thread overview]
Message-ID: <20160920061042.GL9314@birch.djwong.org> (raw)
In-Reply-To: <20160920055945.GG340@dastard>

On Tue, Sep 20, 2016 at 03:59:45PM +1000, Dave Chinner wrote:
> On Mon, Sep 19, 2016 at 09:16:52PM -0700, Darrick J. Wong wrote:
> > On Tue, Sep 13, 2016 at 06:28:42PM +1000, Dave Chinner wrote:
> > > -	__uint32_t		xs_rmap_2_decrement;
> > > -	__uint32_t		xs_rmap_2_lshift;
> > > -	__uint32_t		xs_rmap_2_rshift;
> > > -	__uint32_t		xs_rmap_2_split;
> > > -	__uint32_t		xs_rmap_2_join;
> > > -	__uint32_t		xs_rmap_2_alloc;
> > > -	__uint32_t		xs_rmap_2_free;
> > > -	__uint32_t		xs_rmap_2_moves;
> > > +#define XFSSTAT_END_ABTB_V2		(XFSSTAT_END_BUF+__XBTS_MAX)
> > > +	__uint32_t		xs_abtb_2[__XBTS_MAX];
> > > +#define XFSSTAT_END_ABTC_V2		(XFSSTAT_END_ABTB_V2+__XBTS_MAX)
> > > +	__uint32_t		xs_abtc_2[__XBTS_MAX];
> > > +#define XFSSTAT_END_BMBT_V2		(XFSSTAT_END_ABTC_V2+__XBTS_MAX)
> > > +	__uint32_t		xs_bmbt_2[__XBTS_MAX];
> > > +#define XFSSTAT_END_IBT_V2		(XFSSTAT_END_BMBT_V2+__XBTS_MAX)
> > > +	__uint32_t		xs_ibt_2[__XBTS_MAX];
> > > +#define XFSSTAT_END_FIBT_V2		(XFSSTAT_END_IBT_V2+__XBTS_MAX)
> > > +	__uint32_t		xs_fibt_2[__XBTS_MAX];
> > > +#define XFSSTAT_END_RMAP_V2		(XFSSTAT_END_FIBT_V2+__XBTS_MAX)
> > > +	__uint32_t		xs_rmap_2[__XBTS_MAX];
> > 
> > Are you planning to merge this before or after the refcount btree?
> 
> Doesn't matter - either way I'll fix up one of them on merge into
> the for-next tree...
> 
> > 
> > >  #define XFSSTAT_END_XQMSTAT		(XFSSTAT_END_RMAP_V2+6)
> > >  	__uint32_t		xs_qm_dqreclaims;
> > >  	__uint32_t		xs_qm_dqreclaim_misses;
> > > @@ -229,26 +165,58 @@ struct xfsstats {
> > >  	__uint64_t		xs_read_bytes;
> > >  };
> > >  
> > > +struct xfsstats {
> > > +	union {
> > > +		struct __xfsstats	s;
> > > +		uint32_t		a[XFSSTAT_END_XQMSTAT];
> > > +	};
> > 
> > /me wonders if there ought to be a build time check to make sure that
> > these two are really the same size?  They look all right as is, but
> > I can see myself forgetting to change something and screwing it up. :(
> 
> It isn't the same size, because struct __xfsstats has three u64
> stats at the end that aren't part of the u32 array indexed by
> XFSSTAT_END_XQMSTAT. If we get the calculation of
> XFSSTAT_END_XQMSTAT wrong , then the output of the stats in the proc
> and sysfs files is screwed up because it treats the stats as an
> array of u32 items of that same size.  So it's fairly obvious when
> it gets broken...

Well ok, how about a build time check that the sizes are off by exactly how
much we expect them to be?  I guess I'd eventually notice the /proc output
looking weird after staring at bad numbers for long enough... ;)

<shrug> Your call though. :)

--D

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> --
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