is apparently useful for large shell systems, or systems with long running
idle processes. To enable the feature:
sysctl -w vm.swap_idle_enabled=1
Please note that some of the other vm sysctl variables have been renamed
to be more accurate.
Submitted by: Much of it from Matt Dillon <dillon@best.net>
the maximum pageout rate:
sysctl -w vm.vm_maxlaunder=n
1 < n < inf.
If paging heavily on large systems, it is likely that a performance
improvement can be achieved by increasing the parameter. On a large
system, the parm is 32, but numbers as large as 128 can make a big
difference. If paging is expensive, you might try decreasing the
number to 1-8.
sysctl -w vm.defer_swap_pageouts=1
Causes the system to resist the use of swap space. In low memory
conditions, performance will decrease.
sysctl -w vm.disable_swap_pageouts=1
Causes the system to mostly disable the use of swap space. In
low memory conditions, the system will likely start killing
processes.
the system is out of memory. The daemon does a minimal amount of work that
increases as the system becomes more likely to run out of memory and page in/out.
The default tuning is fairly low in background CPU usage, and sysctl variables
have been added to enable flexable operation. This is an experimental feature
that will likely be changed and improved over time.
changes, so don't expect to be able to run the kernel as-is (very well)
without the appropriate Lite/2 userland changes.
The system boots and can mount UFS filesystems.
Untested: ext2fs, msdosfs, NFS
Known problems: Incorrect Berkeley ID strings in some files.
Mount_std mounts will not work until the getfsent
library routine is changed.
Reviewed by: various people
Submitted by: Jeffery Hsu <hsu@freebsd.org>
This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
anymore with the "full" collapse fix that we added about 1yr ago!!! The
code has been removed by optioning it out for now, so we can put it back
in ASAP if any problems are found.
The default level works with minimal overhead, but one can also enable
full, efficient use of a 512K cache. (Parameters can be generated
to support arbitrary cache sizes also.)
problem with the 'shell scripts' was found, but there was a 'strange'
problem found with a 486 laptop that we could not find. This commit
backs the code back to 25-jul, and will be re-entered after the snapshot
in smaller (more easily tested) chunks.
performance issues.
1) The pmap module has had too many inlines, and so the
object file is simply bigger than it needs to be.
Some common code is also merged into subroutines.
2) Removal of some *evil* PHYS_TO_VM_PAGE macro calls.
Unfortunately, a few have needed to be added also.
The removal caused the need for more vm_page_lookups.
I added lookup hints to minimize the need for the
page table lookup operations.
3) Removal of some bogus performance improvements, that
mostly made the code more complex (tracking individual
page table page updates unnecessarily). Those improvements
actually hurt 386 processors perf (not that people who
worry about perf use 386 processors anymore :-)).
4) Changed pv queue manipulations/structures to be TAILQ's.
5) The pv queue code has had some performance problems since
day one. Some significant scalability issues are resolved
by threading the pv entries from the pmap AND the physical
address instead of just the physical address. This makes
certain pmap operations run much faster. This does
not affect most micro-benchmarks, but should help loaded system
performance *significantly*. DG helped and came up with most
of the solution for this one.
6) Most if not all pmap bit operations follow the pattern:
pmap_test_bit();
pmap_clear_bit();
That made for twice the necessary pv list traversal. The
pmap interface now supports only pmap_tc_bit type operations:
pmap_[test/clear]_modified, pmap_[test/clear]_referenced.
Additionally, the modified routine now takes a vm_page_t arg
instead of a phys address. This eliminates a PHYS_TO_VM_PAGE
operation.
7) Several rewrites of routines that contain redundant code to
use common routines, so that there is a greater likelihood of
keeping the cache footprint smaller.
performance to LRU or worse when RSS limiting takes effect. Also,
make an end condition in the active queue scan more efficient in the
case where pages are removed from the active queue as a side effect
of a pmap operation.
Re-enables the RSS limiting, and the routine is now tail-recursive,
making it much more safe (eliminates the possiblity of kernel stack
overflow.) Also, the RSS limiting is a little more intelligent about
finding the likely objects that are pushing the process over the limit.
Added some sysctls that help with VM system tuning.
New sysctl features:
1) Enable/disable lru pageout algorithm.
vm.pageout_algorithm = 0, default algorithm that works
well, especially using X windows and heavy
memory loading. Can have adverse effects,
sometimes slowing down program loading.
vm.pageout_algorithm = 1, close to true LRU. Works much
better than clock, etc. Does not work as well as
the default algorithm in general. Certain memory
"malloc" type benchmarks work a little better with
this setting.
Please give me feedback on the performance results
associated with these.
2) Enable/disable swapping.
vm.swapping_enabled = 1, default.
vm.swapping_enabled = 0, useful for cases where swapping
degrades performance.
The config option "NO_SWAPPING" is still operative, and
takes precedence over the sysctl. If "NO_SWAPPING" is
specified, the sysctl still exists, but "vm.swapping_enabled"
is hard-wired to "0".
Each of these can be changed "on the fly."
1) Make it much less likely to miss a wakeup in vm_page_free_wakeup
2) Create a new entry point into pmap: pmap_ts_referenced, eliminates
the need to scan the pv lists twice in many cases. Perhaps there
is alot more to do here to work on minimizing pv list manipulation
3) Minor improvements to vm_pageout including the use of pmap_ts_ref.
4) Major changes and code improvement to pmap. This code has had
several serious bugs in page table page manipulation. In order
to simplify the problem, and hopefully solve it for once and all,
page table pages are no longer "managed" with the pv list stuff.
Page table pages are only (mapped and held/wired) or
(free and unused) now. Page table pages are never inactive,
active or cached. These changes have probably fixed the
hold count problems, but if they haven't, then the code is
simpler anyway for future bugfixing.
5) The pmap code has been sorely in need of re-organization, and I
have taken a first (of probably many) steps. Please tell me
if you have any ideas.
queue corruption problems, and to apply Gary Palmer's code cleanups.
David Greenman helped with these problems also. There is still
a hang problem using X in small memory machines.
case where blocking can occur, thereby giving other process's a chance
to modify the queue where a page resides. This could cause numerous
process and system failures.
a condition when blocking can occur, and the daemon did not check properly
for a page remaining on the expected queue. Additionally, the inactive
target was being set much too large for small memory machines. It is now
being calculated based upon the amount of user memory available on every
pageout daemon run. Another problem was that if memory was very low, the
pageout daemon could fail repeatedly to traverse the inactive queue.
contributions or ideas from Stephen McKay <syssgm@devetir.qld.gov.au>,
Alan Cox <alc@cs.rice.edu>, David Greenman <davidg@freebsd.org> and me:
More usage of the TAILQ macros. Additional minor fix to queue.h.
Performance enhancements to the pageout daemon.
Addition of a wait in the case that the pageout daemon
has to run immediately.
Slightly modify the pageout algorithm.
Significant revamp of the pmap/fork code:
1) PTE's and UPAGES's are NO LONGER in the process's map.
2) PTE's and UPAGES's reside in their own objects.
3) TOTAL elimination of recursive page table pagefaults.
4) The page directory now resides in the PTE object.
5) Implemented pmap_copy, thereby speeding up fork time.
6) Changed the pv entries so that the head is a pointer
and not an entire entry.
7) Significant cleanup of pmap_protect, and pmap_remove.
8) Removed significant amounts of machine dependent
fork code from vm_glue. Pushed much of that code into
the machine dependent pmap module.
9) Support more completely the reuse of already zeroed
pages (Page table pages and page directories) as being
already zeroed.
Performance and code cleanups in vm_map:
1) Improved and simplified allocation of map entries.
2) Improved vm_map_copy code.
3) Corrected some minor problems in the simplify code.
Implemented splvm (combo of splbio and splimp.) The VM code now
seldom uses splhigh.
Improved the speed of and simplified kmem_malloc.
Minor mod to vm_fault to avoid using pre-zeroed pages in the case
of objects with backing objects along with the already
existant condition of having a vnode. (If there is a backing
object, there will likely be a COW... With a COW, it isn't
necessary to start with a pre-zeroed page.)
Minor reorg of source to perhaps improve locality of ref.
to help diagnose a problem on wcarchive (where the kernel stack was
sometimes not present), but is useful in its own right since swapping
actually reduces performance on some systems (such as wcarchive).
Note: swapping in this context means making the U pages pageable and has
nothing to do with generic VM paging, which is unaffected by this option.
Reviewed by: <dyson>
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.
Submitted by: terry (terry lambert)
This is a composite of 3 patch sets submitted by terry.
they are:
New low-level init code that supports loadbal modules better
some cleanups in the namei code to help terry in 16-bit character support
some changes to the mount-root code to make it a little more
modular..
NOTE: mounting root off cdrom or NFS MIGHT be broken as I haven't been able
to test those cases..
certainly mounting root of disk still works just fine..
mfs should work but is untested. (tomorrows task)
The low level init stuff includes a total rewrite of init_main.c
to make it possible for new modules to have an init phase by simply
adding an entry to a TEXT_SET (or is it DATA_SET) list. thus a new module can
be added to the kernel without editing any other files other than the
'files' file.
