fuse over iouring

kernel support

"mapfs mount <VolumeName> <MountPoint>" mounts in traditional mode by default;

To enable "fuse over iouring" mode, specify "iouring" during mount:

 $ sudo mapfs mount <VolumeName> <MountPoint> iouring

Note:

Specifying iouring does not guarantee "fuse over iouring" will be enabled. It also requires Linux kernel version >= 6.18, typically from these distributions:

• Amazon Linux 2023, kernel 6.18
• Ubuntu 26.04

Advantages and limitations of iouring mode

Traditional mount:
When CPU number exceeds 16 and IOPS exceeds 300K, a single lock contention point can cause CPU usage to spike while I/O performance may not improve or can even degrade greatly.
The more CPUs added, the worse the performance degradation becomes, due to scheduling pressure, frequent L3 cache invalidations, and the single kernel spinlock CPU usage.

iouring mode mount:
breaks single lock contention and scale up better when CPU number exceeds 16 and IOPS exceed 300K.
However, its limitation is that when IOPS exceed 1M and CPU number reaches 32 or more, fuse uring threads may degrade into polling mode, causing high CPU usage without a corresponding I/O performance increase.