04-24-2002
UBC cache vs. Metadata cache
hi,
What is the difference between UBC cache and Metadata cache ? where can i find UBC cache Hits and Metadata cache Hits in hp-ux?
Advanced thanx for the help.
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UBC(9) BSD Kernel Developer's Manual UBC(9)
NAME
ubc -- unified buffer cache
SYNOPSIS
#include <uvm/uvm.h>
void *
ubc_alloc(struct uvm_object *uobj, voff_t offset, vsize_t *lenp, int advice, int flags);
void
ubc_release(void *va, int flags);
int
ubc_uiomove(struct uvm_object *uobj, struct uio *uio, vsize_t todo, int advice, int flags);
void
ubc_purge(struct uvm_object *uobj);
DESCRIPTION
ubc_alloc() creates a kernel mapping of uobj starting at offset offset. The desired length of the mapping is pointed to by lenp, but the
actual mapping may be smaller than this. lenp is updated to contain the actual length mapped. advice 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)
The possible flags are
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.
Once the mapping is created, it must be accessed only by methods that can handle faults, such as uiomove() or kcopy(). Page faults on the
mapping will result in the object's pager method being called to resolve the fault.
ubc_release() frees the mapping at va for reuse. The mapping may be cached to speed future accesses to the same region of the object. The
flags can be any of
UBC_UNMAP Do not cache mapping.
ubc_uiomove() allocates an UBC memory window, performs I/O on it and unmaps the window. The advice parameter takes the same values as the
respective parameter in ubc_alloc() and the flags parameter takes the same arguments as ubc_alloc() and ubc_release(). Additionally, the
flag UBC_PARTIALOK can be provided to indicate that it is acceptable to return if an error occurs mid-transfer.
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
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 <chuq@chuq.com> designed and implemented the UBC part of UVM, which uses UVM pages to cache vnode data rather than the tradi-
tional buffer cache buffers.
BSD
June 14, 2011 BSD