On 6/9/20 7:09 PM, Hans van Kranenburg wrote:
* (not recommended) If your mount options do not show 'ssd' in them and
your kernel does not have this patch:
https://www.spinics.net/lists/linux-btrfs/msg64203.html then you can try
the mount -o ssd_spread,nossd (read the story in the link above).
Anyway, you're better off moving to something recent instead of trying
all these obsolete workarounds...
I forgot to respond to this in my last email. The version of BTRFS
running in my openSuSE 15.0 kernel does indeed have that patch.
Nevertheless, I tried with just ssd_spread for kicks, and it showed no
major improvement, and had the same growth pathology as past runs had:
0f70583cd12cac:/pandata/0 # time (for i in {1..10}; do time (rm test$i;
sync); done)
real 0m0.636s
real 0m0.649s
real 0m0.417s
real 0m0.562s
real 0m0.381s
real 0m0.949s
real 0m2.014s
real 0m2.129s
real 0m2.074s
real 0m5.114s
Total:
real 0m14.939s
Even more curiously, when I repeat this experiment using ext4 (lazy init
was disabled) on the exact same disks, I see a nearly identical slowdown
pathology:
real 0m0.122s
real 0m0.048s
real 0m0.075s
real 0m0.076s
real 0m0.100s
real 0m0.499s
real 0m1.658s
real 0m1.709s
real 0m1.716s
real 0m6.599s
Total:
real 0m12.614s
Very wonky. Maybe this has something to do with the mdraid we use
underneath both, or maybe it's something architectural I'm not
immediately grasping that impacts all extent-based filesystems. Will
report back when I have blktraces.
Best,
ellis
