Re: MDS cache size limits

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Quoting John Spray (jspray@xxxxxxxxxx):
> On Mon, Jan 8, 2018 at 8:02 PM, Marc Roos <M.Roos@xxxxxxxxxxxxxxxxx> wrote:
> >
> > I guess the mds cache holds files, attributes etc but how many files
> > will the default "mds_cache_memory_limit": "1073741824" hold?
> 
> We always used to get asked how much memory a given mds_cache_size (in
> inodes) would require, I guess it was only a matter of time until the
> reverse question was asked :-)

@Marc Roos: 

{"items":731544591,"bytes":144955142984}

Bytes used is actually: 235604586496 (RES), 248868077568 (VIRT). 

So:

1073741824/235604586496
.00455738931049302623
.*731544591
3333933.49917239288177762193
./(1000^2)
3.33393349917239288177

~ around 3 Milion "items" for 1 GiB

More details below.

ceph daemon mds.mds2 perf dump | jq

  },
  "mds_mem": {
    "ino": 45358896,
    "ino+": 268519704,
    "ino-": 223160808,
    "dir": 31856591,
    "dir+": 199761898,
    "dir-": 167905307,
    "dn": 45358896,
    "dn+": 281905135,
    "dn-": 236546239,
    "cap": 3000076,
    "cap+": 300470635,
    "cap-": 297470559,
    "rss": 230082340,
    "heap": 313884,
    "buf": 0
},

ceph daemon mds.mds2 dump_mempools | jq

  },
  "mds_co": {
    "items": 731544591,
    "bytes": 144955142984
  },
...
...
  },
  "total": {
    "items": 1482069569,
    "bytes": 145738337213
  }

Gr. Stefan

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