K 10
svn:author
V 3
kib
K 8
svn:date
V 27
2018-05-13T09:47:28.498423Z
K 7
svn:log
V 722
Detect and optimize reads from the hole on UFS.

- Create getblkx(9) variant of getblk(9) which can return error.
- Add GB_NOSPARSE flag for getblk()/getblkx() which requests that BMAP
  was performed before the buffer is created, and EJUSTRETURN returned
  in case the requested block does not exist.
- Make ffs_read() use GB_NOSPARSE to avoid instantiating buffer (and
  allocating the pages for it), copying from zero_region instead.

The end result is less page allocations and buffer recycling when a
hole is read, which is important for some benchmarks.

Requested and reviewed by:	jeff
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D14917

END