Firstly, now our read-ahead clustering is on a file descriptor basis and not
on a per-vnode basis. This will allow multiple processes reading the
same file to take advantage of read-ahead clustering. Secondly, there
previously was a problem with large reads still using the ramp-up
algorithm. Of course, that was bogus, and now we read the entire
"chunk" off of the disk in one operation. The read-ahead clustering
algorithm should use less CPU than the previous also (I hope :-)).
NOTE: THAT LKMS MUST BE REBUILT!!!
scheme. Additionally, add the capability for checking for unexpected
kernel page faults. The maximum amount of kva space for buffers hasn't
been decreased from where it is, but it will now be possible to do so.
This scheme manages the kva space similar to the buffers themselves. If
there isn't enough kva space because of usage or fragementation, buffers
will be reclaimed until a buffer allocation is successful. This scheme
should be very resistant to fragmentation problems until/if the LFS code
is fixed and uses the bogus buffer locking scheme -- but a 'fixed' LFS
is not likely to use such a scheme.
Now there should be NO problem allocating buffers up to MAXPHYS.
Major: When blocking occurs in allocbuf() for VMIO files,
excess wire counts could accumulate.
Major: Pages are incorrectly accumulated into the physical
buffer for clustered reads. This happens when bogus
page is needed.
Minor: When reclaiming buffers, the async flag on the buffer
needs to be zero, or the reclaim is not optimal.
Minor: The age flag should be cleared, if a buffer is wanted.
code without the B_READ flag being set. This is a problem when the
data is not cached, and the result will be a bogus attempted write.
Submitted by: Kato Takenori <kato@eclogite.eps.nagoya-u.ac.jp>
queue type is not set to QUEUE_NONE. This appears to have
caused a hang bug that has been lurking.
2) Fix bugs that brelse'ing locked buffers do not "free" them, but the
code assumes so. This can cause hangs when LFS is used.
3) Use malloced memory for directories when applicable. The amount
of malloced memory is seriously limited, but should decrease the
amount of memory used by an average directory to 1/4 - 1/2 previous.
This capability is fully tunable. (Note that there is no config
parameter, and might never be.)
4) Bias slightly the buffer cache usage towards non-VMIO buffers. Since
the data in VMIO buffers is not lost when the buffer is reclaimed, this
will help performance. This is adjustable also.
Speed up for vfs_bio -- addition of a routine bqrelse to greatly diminish
overhead for merged cache.
Efficiency improvement for vfs_cluster. It used to do alot of redundant
calls to cluster_rbuild.
Correct the ordering for vrele of .text and release of credentials.
Use the selective tlb update for 486/586/P6.
Numerous fixes to the size of objects allocated for files. Additionally,
fixes in the various pagers.
Fixes for proper positioning of vnode_pager_setsize in msdosfs and ext2fs.
Fixes in the swap pager for exhausted resources. The pageout code
will not as readily thrash.
Change the page queue flags (PG_ACTIVE, PG_INACTIVE, PG_FREE, PG_CACHE) into
page queue indices (PQ_ACTIVE, PQ_INACTIVE, PQ_FREE, PQ_CACHE),
thereby improving efficiency of several routines.
Eliminate even more unnecessary vm_page_protect operations.
Significantly speed up process forks.
Make vm_object_page_clean more efficient, thereby eliminating the pause
that happens every 30seconds.
Make sequential clustered writes B_ASYNC instead of B_DELWRI even in the
case of filesystems mounted async.
Fix a panic with busy pages when write clustering is done for non-VMIO
buffers.
1) Make cluster buffer list be a non-malloced chain. This eliminates
yet another 'evil' M_WAITOK and generally cleans up the code.
2) Fix write clustering for ext2fs. It was just broken. Also, ffs
clustering had an efficiency problem that more bawrites were happening
than should have been.
3) Make changes to buf.h to support the above, plus remove b_pfcent
at the request of David Greenman.
Reviewed by: davidg (partially)
support for EXT2FS. Note that the Sig-11 problems appear to be caused by
this, but there is still probably an underlying VM problem that let this
clustering bug cause vnode objects to appear to be corrupted.
The direct manifestation of this bug would have been severely mis-read
files. It is possible that processes would Sig-11 on very damaged
input files and might explain the mysterious differences in system
behaviour when phk's malloc is being used.
Better performance -- more aggressive read-ahead
under certain circumstanses.
Mods to support clustering on small
( < PAGE_SIZE) block size filesystems (e.g. ext2fs,
msdosfs.)
Various more tweaks from John Dyson to improve read ahead calculations.
vfs_subr.c:
Only wakeup if numoutput is 0 in vwakeup().
Submitted by: John Dyson
implemented the ability to limit bufferspace by memory consumed. (vfs_bio.c)
Fixed recently introduced bugs that caused extra I/O to happen in some
cases. (vfs_cluster.c)
Submitted by: John Dyson
much higher filesystem I/O performance, and much better paging performance. It
represents the culmination of over 6 months of R&D.
The majority of the merged VM/cache work is by John Dyson.
The following highlights the most significant changes. Additionally, there are
(mostly minor) changes to the various filesystem modules (nfs, msdosfs, etc) to
support the new VM/buffer scheme.
vfs_bio.c:
Significant rewrite of most of vfs_bio to support the merged VM buffer cache
scheme. The scheme is almost fully compatible with the old filesystem
interface. Significant improvement in the number of opportunities for write
clustering.
vfs_cluster.c, vfs_subr.c
Upgrade and performance enhancements in vfs layer code to support merged
VM/buffer cache. Fixup of vfs_cluster to eliminate the bogus pagemove stuff.
vm_object.c:
Yet more improvements in the collapse code. Elimination of some windows that
can cause list corruption.
vm_pageout.c:
Fixed it, it really works better now. Somehow in 2.0, some "enhancements"
broke the code. This code has been reworked from the ground-up.
vm_fault.c, vm_page.c, pmap.c, vm_object.c
Support for small-block filesystems with merged VM/buffer cache scheme.
pmap.c vm_map.c
Dynamic kernel VM size, now we dont have to pre-allocate excessive numbers of
kernel PTs.
vm_glue.c
Much simpler and more effective swapping code. No more gratuitous swapping.
proc.h
Fixed the problem that the p_lock flag was not being cleared on a fork.
swap_pager.c, vnode_pager.c
Removal of old vfs_bio cruft to support the past pseudo-coherency. Now the
code doesn't need it anymore.
machdep.c
Changes to better support the parameter values for the merged VM/buffer cache
scheme.
machdep.c, kern_exec.c, vm_glue.c
Implemented a seperate submap for temporary exec string space and another one
to contain process upages. This eliminates all map fragmentation problems
that previously existed.
ffs_inode.c, ufs_inode.c, ufs_readwrite.c
Changes for merged VM/buffer cache. Add "bypass" support for sneaking in on
busy buffers.
Submitted by: John Dyson and David Greenman
