UBC(9) FreeBSD Kernel Developer's Manual UBC(9)
NAME
ubc - unified buffer cache
SYNOPSIS
#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);
DESCRIPTION
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.
CODE REFERENCES
The ubc subsystem is implemented within the file sys/uvm/uvm_bio.c.
SEE ALSO
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.
HISTORY
UBC first appeared in NetBSD 1.6.
AUTHORS
Chuck Silvers <
[email protected]> designed and implemented the UBC part of
UVM, which uses UVM pages to cache vnode data rather than the traditional
buffer cache buffers.
FreeBSD 14.1-RELEASE-p8 May 12, 2018 FreeBSD 14.1-RELEASE-p8