Roch Bourbonnais - Performance Engineering schrieb:
A already noted, this needs not be different from other FS
but is still an interesting question. I'll touch 3 aspects
here
- reported freemem
- syscall writes to mmap pages
- application write throttling
Reported freemem will be lower when running with ZFS than
say UFS. The UFS page cache is considered as freemem. ZFS
will return it's 'cache' only when memory is needed. So you
will operate with lower freemem but won't actually suffer
from this.
The RAM usage should be made more transparent to the administrator. Just
today, after installing snv_37 on another machine, I couldn't disable swap
because zfs has grabbed all free memory it could get and didn't release it
(even after a "zfs export"):
# swap -l
swapfile dev swaplo blocks free
/dev/md/dsk/d2 85,4 8 4193272 4193272
# swap -s
total: 275372k bytes allocated + 93876k reserved = 369248k used, 1899492k
available
# swap -d /dev/md/dsk/d2
/dev/md/dsk/d2: Not enough space
# kstat | grep pp_kernel
pp_kernel 872514
# prtconf | head -2
System Configuration: Sun Microsystems i86pc
Memory size: 4095 Megabytes
# zpool export pool
# zpool list
no pools available
# swap -d /dev/md/dsk/d2
This was shortly after installation with not much running on the machine. To
speed up 'mirroring' of swap I usually do the following (but couldn't in
this case):
swap -d /dev/md/dsk/d2
metaclear d2
metainit d2 -m d21 d22 0
swap -a /dev/md/dsk/d2
Daniel
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