From owner-freebsd-stable@freebsd.org  Tue Nov 10 09:58:49 2015
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To: FreeBSD <freebsd-stable@freebsd.org>
From: "Eugene M. Zheganin" <emz@norma.perm.ru>
Subject: zfs, mc, mcview and files opening
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Hi.

my midnight commander is terribly slow at vieweing files with mcview.
Opening of a file of approximately 10 megabytes takes about 30-40
seconds. This isn't related with the compression setting, %busy wait or
pool properties- I tested on various machines, it's fully reproducible.
This lag appears on files about 1.5 megs in size, and the lag time is
pretty constant.  From my observation, it's the following syscall that's
blocking:

fstat(4,{ mode=p--------- ,inode=41,size=0,blksize=4096 }) = 0 (0x0)
(observed using `truss mcview maillog`)

If the file is viewed not by mcview (i.e. it is of a special type and
viewed by the special utility, or mcview is simply not used - for
example more opens same file without lag) - the file is opening fast as
always. When mcview is involved - lag appears. In the same time I've
never seen this lag on filesystems other than zfs. And the most
beautiful detail is that this lag is repeatable on multiple opens of
same file - though you can expect that it will be only first time that
would be that slow, it doesn't happen - same pause occurs on sequential
opens.

Who's issue is this ?
Can some workaround be used ?

Thanks.
Eugene.