cachestat

query the page cache statistics of a file

sys_cachestat(unsigned int fd, struct cachestat_range *cstat_range, struct cachestat *cstat, unsigned int flags)

register	value
`r2`	451, the syscall number
`r4`	unsigned int fd
`r5`	struct cachestat_range *cstat_range
`r6`	struct cachestat *cstat
`r7`	unsigned int flags
`r2`	the return value

Then run trap to enter the kernel.

Same syscall on other architectures