ZFS buffer/cache is counted under used memory

[borutmrak]

I'm running zfsonlinux and htop is counting the ZFS ARC (memory) cache under normal used memory.

This is because ZFS doesn't use normal Linux memory cache but it's own version.

It would be useful if htop could detect if ZFS is running (maybe checking for /dev/zfs) and in that case show the memory used by ZFS cache in a different colour or maybe joined with the normal buffers/cache.

ARC used memory can be checked in /proc/spl/kstat/zfs/arcstats (size):

# grep ^size /proc/spl/kstat/zfs/arcstats 
size                            4    3533162592

[hishamhm]

But does it behave like normal Linux memory cache? (ie, is it a kernelspace cache and if other programs need the memory does it relinquish it?)

[borutmrak]

Yes, it does.

The limits for the cache are set in /sys/module/zfs/parameters/zfs_arc_max and /sys/module/zfs/parameters/zfs_arc_min, so there might be a minimum amount that is always in use, but the default is 0.

[flaviut]

It looks like ARC space is considered correctly on FreeBSD, but not Linux.

Is this bug something you're willing to re-open?

[xornet-sl]

@hishamhm Please, could you consider adding this feature for linux?
It would be great if I could see ARC statistics by different color in memory bar and as a different counter!
It would be very useful feature!

[Harvie]

This is still a problem. Can you please take a look at it?