Re: [RFC PATCH] ceph: add remote object copy counter to fs client

[Jeff Layton]

On Thu, 2021-10-21 at 12:18 -0400, Patrick Donnelly wrote:
> On Thu, Oct 21, 2021 at 11:44 AM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> > 
> > On Thu, 2021-10-21 at 09:52 -0400, Patrick Donnelly wrote:
> > > On Wed, Oct 20, 2021 at 12:27 PM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> > > > 
> > > > On Wed, 2021-10-20 at 15:37 +0100, Luís Henriques wrote:
> > > > > This counter will keep track of the number of remote object copies done on
> > > > > copy_file_range syscalls.  This counter will be filesystem per-client, and
> > > > > can be accessed from the client debugfs directory.
> > > > > 
> > > > > Cc: Patrick Donnelly <pdonnell@xxxxxxxxxx>
> > > > > Signed-off-by: Luís Henriques <lhenriques@xxxxxxx>
> > > > > ---
> > > > > This is an RFC to reply to Patrick's request in [0].  Note that I'm not
> > > > > 100% sure about the usefulness of this patch, or if this is the best way
> > > > > to provide the functionality Patrick requested.  Anyway, this is just to
> > > > > get some feedback, hence the RFC.
> > > > > 
> > > > > Cheers,
> > > > > --
> > > > > Luís
> > > > > 
> > > > > [0] https://github.com/ceph/ceph/pull/42720
> > > > > 
> > > > 
> > > > I think this would be better integrated into the stats infrastructure.
> > > > 
> > > > Maybe you could add a new set of "copy" stats to struct
> > > > ceph_client_metric that tracks the total copy operations done, their
> > > > size and latency (similar to read and write ops)?
> > > 
> > > I think it's a good idea to integrate this into "stats" but I think a
> > > local debugfs file for some counters is still useful. The "stats"
> > > module is immature at this time and I'd rather not build any qa tests
> > > (yet) that rely on it.
> > > 
> > > Can we generalize this patch-set to a file named "op_counters" or
> > > similar and additionally add other OSD ops performed by the kclient?
> > > 
> > 
> > 
> > Tracking this sort of thing is the main purpose of the stats code. I'm
> > really not keen on adding a whole separate set of files for reporting
> > this.
> 
> Maybe I'm confused. Is there some "file" which is already used for
> this type of debugging information? Or do you mean the code for
> sending stats to the MDS to support cephfs-top?
> 
> > What's the specific problem with relying on the data in debugfs
> > "metrics" file?
> 
> Maybe no problem? I wasn't aware of a "metrics" file.
> 

Yes. For instance:

# cat /sys/kernel/debug/ceph/*/metrics
item                               total
------------------------------------------
opened files  / total inodes       0 / 4
pinned i_caps / total inodes       5 / 4
opened inodes / total inodes       0 / 4

item          total       avg_lat(us)     min_lat(us)     max_lat(us)     stdev(us)
-----------------------------------------------------------------------------------
read          0           0               0               0               0
write         5           914013          824797          1092343         103476
metadata      79          12856           1572            114572          13262

item          total       avg_sz(bytes)   min_sz(bytes)   max_sz(bytes)  total_sz(bytes)
----------------------------------------------------------------------------------------
read          0           0               0               0               0
write         5           4194304         4194304         4194304         20971520

item          total           miss            hit
-------------------------------------------------
d_lease       11              0               29
caps          5               68              10702


I'm proposing that Luis add new lines for "copy" to go along with the
"read" and "write" ones. The "total" counter should give you a count of
the number of operations.
 
-- 
Jeff Layton <jlayton@xxxxxxxxxx>