Since upgrading from 11.1-RELEASE p10 to 11.2-BETA3 on amd64 we are seeing excessive swapping, even when the system is idle. Swap is on zvol, with system constantly swapping in/out for no apparent reason. There is no load on the system: 5:22PM up 1 day, 7 mins, 1 user, load averages: 0.06, 0.20, 0.18 However the following lines from top confirm that excessive swapping is occurring: Swap: 4096M Total, 158M Used, 3938M Free, 3% Inuse, 448K In, 136K Out Swap: 4096M Total, 156M Used, 3940M Free, 3% Inuse, 8K In, 44K Out Swap: 4096M Total, 157M Used, 3939M Free, 3% Inuse, 332K In, 24K Out etc.... System has 64GB of RAM, 8-core Xeon E5-2620 v4 CPU, all memory and ZFS tunables are at defaults. ZFS settings that were changed on swap zvol are: volblocksize 4K sync always compression off The following process seems to constantly active: pagedaemon{laundry: dom0} Did not exhibit this behaviour on 11.1-RELEASE with exactly the same configuration.
issue still exists on 11.2-RC2. have deployed 11.2-RC2 onto another system and are seeing the same behaviour of excessive swapping. reducing vfs.zfs.arc_max seems to help reduce the swapping.
I have the same issue, albeit with swapping to a gmirror device instead of a zvol. Bug #224975 may be related. The following thread seems to be related: https://lists.freebsd.org/pipermail/freebsd-stable/2018-June/089132.html I am now trying the patch in https://reviews.freebsd.org/D7538 (mentioned in that thread). In general one can say that there has been a massive regression regarding ZFS + swap between 11.1 and 11.2. -- Martin
I have now deployed D7538 on three machines that had all been affected by excessive swapping. So far their swap usage stays at zero. I have yet to check what happens under memory pressure. -- Martin
It seems that with this patch the ARC still grows until the system starts to swap again. "swapoff -a" results in "swapoff: /dev/mirror/swap: Cannot allocate memory" In 11.1 this used to work. Also, using "sysctl vfs.zfs.arc_max=xxxxxxxxxx" to reduce the size of the ARC cache does not seem to free memory (top shows that wired memory remains unchanged). ZFS + swap is very broken under 11.2. -- Martin