ZFS slow reads for unallocated blocks

[Adam Nowacki]

http://tepeserwery.pl/nowak/freebsd/zfs_sparse_optimization.patch.txt

Does it look sane?

On 2013-04-12 09:03, Andriy Gapon wrote:
>
> ENOTIME to really investigate, but here is a basic profile result for those
> interested:
>                kernel`bzero+0xa
>                kernel`dmu_buf_hold_array_by_dnode+0x1cf
>                kernel`dmu_read_uio+0x66
>                kernel`zfs_freebsd_read+0x3c0
>                kernel`VOP_READ_APV+0x92
>                kernel`vn_read+0x1a3
>                kernel`vn_io_fault+0x23a
>                kernel`dofileread+0x7b
>                kernel`sys_read+0x9e
>                kernel`amd64_syscall+0x238
>                kernel`0xffffffff80747e4b
>
> That's where > 99% of time is spent.
>