zfs, a directory that used to hold lot of files and listing pause

[Eugene M. Zheganin]

Hi.

I have FreeBSD 10.2-STABLE r289293 (but I have observed this situation 
on different releases) and a zfs. I also have one directory that used to 
have a lot of (tens of thousands) files. I surely takes a lot of time to 
get a listing of it. But now I have 2 files and a couple of dozens 
directories in it (I sorted files into directories). Surprisingly, 
there's still a lag between "ls" and an output:


===Cut===

# /usr/bin/time -h ls
.recycle        2016-01         2016-04         2016-07 2016-10         
sort-files.sh
2014            2016-02         2016-05         2016-08 ktrace.out      
sort-months.sh
2015            2016-03         2016-06         2016-09 old             
sounds
         5.75s real              0.00s user              0.02s sys

===Cut===


I've seen this situation before, on other servers, so it's not the first 
time I encounter this. However, it's not 100% reproducible (I mean, if I 
fill the directory with dozens of thousands of files, I will not 
certainly get this lag after the deletion).

Has anyone seen this and does anyone know how to resolve this ? It's not 
critical issue, but it makes thing uncomfortable here. One method I'm 
aware of: you can move the contents of this directory to some other 
place, then delete it and create again. But it's kind of a nasty workaround.


Thanks.

Eugene.