FUSE: write operations trigger balance_dirty_pages when using writeback cache

[刘硕然]

Dear Miklos,

Recently I've been testing FUSE and libfuse example passthrough_ll with writeback cache on, and found out that the performance drops significantly compared to that in local filesystem. As I can see from trace, balance_dirty_pages is triggered very frequently even if there not enough pages that shall be sent to libfuse. I'm not sure if this is a known fact or the FUSE writeback feature requires some specific configurations. Trace log is attached.

dd-19067 [001] .... 195295.568097: balance_dirty_pages: bdi 0:42: limit=3180390 setpoint=2782421 dirty=5 bdi_setpoint=0 bdi_dirty=32 dirty_ratelimit=32 task_ratelimit=0 dirtied=32 dirtied_pause=32 paused=0 pause=33 period=33 think=0 cgroup_ino=1
dd-19067 [001] .... 195295.602029: balance_dirty_pages: bdi 0:42: limit=3180390 setpoint=2782421 dirty=5 bdi_setpoint=0 bdi_dirty=33 dirty_ratelimit=32 task_ratelimit=0 dirtied=1 dirtied_pause=0 paused=0 pause=34 period=34 think=1 cgroup_ino=1
dd-19067 [001] .... 195295.637026: balance_dirty_pages: bdi 0:42: limit=3180390 setpoint=2782421 dirty=5 bdi_setpoint=0 bdi_dirty=34 dirty_ratelimit=32 task_ratelimit=0 dirtied=1 dirtied_pause=0 paused=0 pause=35 period=35 think=1 cgroup_ino=1

BTW, I'm using Linux kernel 4.17.12 and libfuse 3.2.5. Look forward to hearing from you. Thanks in advance.

Regards,
Shuoran Liu