ubc —
unified buffer cache
#include
<uvm/uvm.h>
int
ubc_uiomove(
struct
uvm_object *uobj,
struct uio *uio,
vsize_t todo,
int advice,
int flags);
void
ubc_zerorange(
struct
uvm_bject *uobj,
off_t off,
size_t len,
int flags);
void
ubc_purge(
struct
uvm_object *uobj);
ubc_uiomove() allocates an UBC memory window,
performs I/O on it and unmaps the window. The
advice parameter is the access pattern hint,
which must be one of
- UVM_ADV_NORMAL
- No hint
- UVM_ADV_RANDOM
- Random access hint
- UVM_ADV_SEQUENTIAL
- Sequential access hint (from lower offset to higher offset)
and the
flags parameter is
- UBC_READ
- Mapping will be accessed for read.
- UBC_WRITE
- Mapping will be accessed for write.
- UBC_FAULTBUSY
- Fault in window's pages already during mapping operation. Makes sense only
for write.
- UBC_UNMAP
- Do not cache mapping.
- UBC_PARTIALOK
- Indicate that it is acceptable to return if an error occurs
mid-transfer.
UBC memory window is a kernel mapping of
uobj
starting at offset
offset.
Once the mapping is created, it must be accessed only by methods that can handle
faults, such as
uiomove(9)
or
kcopy(9).
Page faults on the mapping will result in the object's pager method being
called to resolve the fault.
Size of individual UBC memory window is limited to
ubc_winsize.
ubc_uiomove() sequentially creates the UBC
memory windows to eventually process the whole range according to
offset and
len parameters.
The mappings may be cached to speed future accesses to the same region of the
object, unless
UBC_UNMAP was specified in
flags parameter.
ubc_zerorange() sets a range of bytes in a
UVM object to zero. The
flags parameter takes
the same arguments as
ubc_uiomove().
ubc_purge() disassociates all UBC structures
from an empty UVM object, specified by
uobj.
The
ubc subsystem is implemented within the
file
sys/uvm/uvm_bio.c.
kcopy(9),
pmap(9),
uiomove(9),
uvm(9),
vnode(9),
vnodeops(9)
Chuck Silvers,
UBC: An Efficient Unified I/O and Memory Caching Subsystem
for NetBSD, Proceedings of the FREENIX Track: 2000
USENIX Annual Technical Conference, USENIX Association,
http://www.usenix.org/event/usenix2000/freenix/full_papers/silvers/silvers.pdf,
285-290, June 18-23,
2000.
UBC first appeared in
NetBSD 1.6.
Chuck Silvers
<
chuq@chuq.com>
designed and implemented the UBC part of UVM, which uses UVM pages to cache
vnode data rather than the traditional buffer cache buffers.