because there was a concensus on current in regards to leaving bss r+w+x
instead of r+w. This is in order to maintain reasonable compatibility
with existing JIT compilers (e.g. kaffe) and possibly other programs.
no major operational changes were made. The three core object->memq loops
were moved into a single inline procedure and various operational
characteristics of the collapse function were documented.
PQ_FREE. There is little operational difference other then the kernel
being a few kilobytes smaller and the code being more readable.
* vm_page_select_free() has been *greatly* simplified.
* The PQ_ZERO page queue and supporting structures have been removed
* vm_page_zero_idle() revamped (see below)
PG_ZERO setting and clearing has been migrated from vm_page_alloc()
to vm_page_free[_zero]() and will eventually be guarenteed to remain
tracked throughout a page's life ( if it isn't already ).
When a page is freed, PG_ZERO pages are appended to the appropriate
tailq in the PQ_FREE queue while non-PG_ZERO pages are prepended.
When locating a new free page, PG_ZERO selection operates from within
vm_page_list_find() ( get page from end of queue instead of beginning
of queue ) and then only occurs in the nominal critical path case. If
the nominal case misses, both normal and zero-page allocation devolves
into the same _vm_page_list_find() select code without any specific
zero-page optimizations.
Additionally, vm_page_zero_idle() has been revamped. Hysteresis has been
added and zero-page tracking adjusted to conform with the other changes.
Currently hysteresis is set at 1/3 (lo) and 1/2 (hi) the number of free
pages. We may wish to increase both parameters as time permits. The
hysteresis is designed to avoid silly zeroing in borderline allocation/free
situations.
attempt to optimize forks but were essentially given-up on due to
problems and replaced with an explicit dup of the vm_map_entry structure.
Prior to the removal, they were entirely unused.
rather then VM_PROT_ALL. obreak, on the otherhand, uses VM_PROT_ALL.
This prevents vm_map_insert() from being able to coalesce the heap and
creates an extra map entry. Since current architectures ignore
VM_PROT_EXECUTE anyway, and since not having VM_PROT_EXECUTE on data/bss
may provide protection in the future, obreak now uses read+write rather
then all (r+w+x).
This is an optimization, not a bug fix.
Submitted by: Alan Cox <alc@cs.rice.edu>
Since paging is in progress, page scan in vm_page_qcollapse() must be
protected at atleast splbio() to prevent pages from being ripped out from
under the scan.
The vm_map_insert()/vm_object_coalesce() optimization has been extended
to include OBJT_SWAP objects as well as OBJT_DEFAULT objects. This is
possible because it costs nothing to extend an OBJT_SWAP object with
the new swapper. We can't do this with the old swapper. The old swapper
used a linear array that would have had to have been reallocated, costing
time as well as a potential low-memory deadlock.
in vm_map_simplify_entry. Basically, once you've verified that
the objects in the adjacent vm_map_entry's are the same, either
NULL or the same vm_object, there's no point in checking that the
objects have the same behavior.
Obtained from: Alan Cox <alc@cs.rice.edu>
Checked by: "Richard Seaman, Jr." <dick@tar.com>
Fix the following problem:
As the code stands now, growing any stack, and not just the process's
main stack, modifies vm->vm_ssize. This is inconsistent with the code
earlier in the same procedure.
This changes the definitions of a few items so that structures are the
same whether or not the option itself is enabled. This allows
people to enable and disable the option without recompilng the world.
As the author says:
|I ran into a problem pulling out the VM_STACK option. I was aware of this
|when I first did the work, but then forgot about it. The VM_STACK stuff
|has some code changes in the i386 branch. There need to be corresponding
|changes in the alpha branch before it can come out completely.
what is done:
|
|1) Pull the VM_STACK option out of the header files it appears in. This
|really shouldn't affect anything that executes with or without the rest
|of the VM_STACK patches. The vm_map_entry will then always have one
|extra element (avail_ssize). It just won't be used if the VM_STACK
|option is not turned on.
|
|I've also pulled the option out of vm_map.c. This shouldn't harm anything,
|since the routines that are enabled as a result are not called unless
|the VM_STACK option is enabled elsewhere.
|
|2) Add what appears to be appropriate code the the alpha branch, still
|protected behind the VM_STACK switch. I don't have an alpha machine,
|so we would need to get some testers with alpha machines to try it out.
|
|Once there is some testing, we can consider making the change permanent
|for both i386 and alpha.
|
[..]
|
|Once the alpha code is adequately tested, we can pull VM_STACK out
|everywhere.
|
Submitted by: "Richard Seaman, Jr." <dick@tar.com>
This takes the conditionals out of the code that has been tested by
various people for a while.
ps and friends (libkvm) will need a recompile as some proc structure
changes are made.
Submitted by: "Richard Seaman, Jr." <dick@tar.com>
vm_page_rename(), but never pulled the page off PQ_CACHE if it was on
PQ_CACHE. Dirty pages in PQ_CACHE are not allowed and a KASSERT was
added in -4.x to test for this... and got hit.
In -4.x, vm_page_rename() automatically dirties the page. This commit
also has it deal with the PQ_CACHE case, deactivating the page in that
case.
values. The 'int' return value for the procedure was never used and
not well defined in any case when there are mixed errors on pages, so
it has been removed. vm_pager_put_pages() and associated vm_pager
functions now return void.
swap blocks are now in PAGE_SIZE'd increments instead of DEV_BSIZE'd
increments. We still convert to DEV_BSIZE'd increments for the
backing store I/O, but everything else is in PAGE_SIZE increments.
vm_pager.h
Added argument to getpbuf() and relpbuf() to allow each subsystem to
specify a different hard limit on the number of simultanious physical
bufferes that said subsystem may allocate. Without this feature, one
subsystem ( e.g. the vfs clustering code ) could hog *ALL* the pbufs,
causing a deadlock in the pager in a low memory situation.
Same for trypbuf().
Removed call to vm_object_collapse(), which can block. This was being
called without the pageout code holding any sort of reference on the
vm_object or vm_page_t structures being manipulated. Since this code
can block, it was possible for other kernel code to shred the state
the pageout code was assuming remained intact.
Fixed potential blocking condition in vm_pageout_page_free() ( which
could cause a deadlock in a low-memory situation ).
Currently there is a hack in-place to deal with clean filesystem meta-data
polluting the inactive page queue. John doesn't like the hack, and neither
do I.
Revamped and commented a portion of the pageout loop.
Added protection against potential memory deadlocks with OBJT_VNODE
when using VOP_ISLOCKED(). The problem is that vp->v_data can be NULL
which causes VOP_ISLOCKED() to return a less informed answer.
remove vm_pager_sync() -- none of the pagers use it any more ( the old
swapper used to. The new one does not ).
reducing the size of vm_page_t.
SWAPBLK_NONE and SWAPBLK_MASK are defined here. These actually are
more generalized then their names imply, but their placement is somewhat
of a legacy issue from a prior test version of this code that put
the swapblk in the vm_page_t structure. That test code was eventually
thrown away. The legacy remains.
Added vm_page_flash() inline. Similar to vm_page_wakeup() except that
it does not clear PG_BUSY ( one assumes that PG_BUSY is already clear ).
Used by a number of routines to wakeup waiters.
Collapsed some of the code in inline calls to make other inline calls.
GCC will optimize this well and it reduces duplication.
vm_page_free() and vm_page_free_zero() inlines added to convert to
the proper vm_page_free_toq() call.
vm_page_sleep_busy() inline added, replacing vm_page_sleep() ( which has
been removed ). This implements a much more optimizable page-waiting
function.
pointers per entry ). The table has been changed to a singly linked
list of vm_page_t pointers. The table has been doubled in size, but
the entries only take half the space so a net-zero change in memory use.
The hash function has been changed, hopefully for the better. The
combination of the larger hash table size of changed function should
keep the chain length down to a reasonable number (0-3, average 1).
vm_object->page_hint has been removed. This 'optimization' was not
only never needed, but costs as much as a hash chain link to implement.
While having page_hint in vm_object might result in better locality
of reference, the cost is not worth the space in vm_object or the
extra instructions in my view.
vm_page_alloc*() functions have been inlined and call a generalized
non-inlined vm_page_alloc_toq() which combines the standard alloc
and zero-page alloc functions together, reducing code size and the L1
cache footprint. Some reordering has been done... not much. The
delinking code should be faster ( because unlinking a doubly-linked list
requires four memory ops and unlinking a singly linked list only requires
two ), and we get a hash consistancy check for free.
vm_page_rename() now automatically sets the page's dirty bits.
vm_page_alloc() does not try to manually inline freeing a cache page.
Instead, it now properly calls vm_page_free(m) ... vm_page_free() is
really too complex to manually inline.
vm_await(), supporting asleep(), has been added.
of most of the swap-pager-specific fields, the removal of the id,
and the removal of paging_offset.
A new inline, vm_object_pip_wakeupn() has been added to subtract an
arbitrary number n from the paging_in_progress count and then wakeup
waiters as necessary. n may be 0, resulting in a 'flash'.
object->paging_offset has been removed - it was used to optimize a
single OBJT_SWAP collapse case yet introduced massive confusion throughout
vm_object.c. The optimization was inconsequential except for the
claim that it didn't have to allocate any memory. The optimization
has been removed.
madvise() has been fixed. The old madvise() could be made to operate
on shared objects which is a big no-no. The new one is much more careful
in what it modifies. MADV_FREE was totally broken and has now been fixed.
vm_page_rename() now automatically dirties a page, so explicit dirtying
of the page prior to calling vm_page_rename() has been removed.
about conversions of objects to OBJT_SWAP, it is done automatically
now.
Replaced manually inserted code with inline calls for busy waiting on
pages, which also incidently fixes a potential PG_BUSY race due to
the code not running at splvm().
vm_objects no longer have a paging_offset field ( see vm/vm_object.c )
instead to properly handle any waiters.
Added comments, added support for M_ASLEEP. Generally treat M_ flags
as flags instead of constants to compare against.
and the swap_pager has been completely replaced.
The new swap pager uses the new blist radix-tree based bitmap allocator
for low level swap allocation and deallocation. The new allocator
is effectively O(5) while the old one was O(N), and the new allocator
allocates all required memory at init time rather then at allocate
memory on the fly at run time.
Swap metadata is allocated in clusters and stored in a hash table,
eliminating linearly allocated structures.
Many, many features have been rewritten or added. Swap space is now
reallocated on the fly providing a poor-mans auto defragmentation of
swap space. Swap space that is no longer needed is freed on a timely
basis so no garbage collection is necessary.
Swap I/O is marked B_ASYNC and NFS has been fixed to do the right
thing with it, so NFS-based paging now has around 10x the performance
as it did before ( previously NFS enforced synchronous I/O for paging ).
changes to the VM system to support the new swapper, VM bug
fixes, several VM optimizations, and some additional revamping of the
VM code. The specific bug fixes will be documented with additional
forced commits. This commit is somewhat rough in regards to code
cleanup issues.
Reviewed by: "John S. Dyson" <root@dyson.iquest.net>, "David Greenman" <dg@root.com>
shared signal handling when there is shared signal handling being
used.
This removes the main objection to making the shared signal handling
a standard ability in rfork() and friends and 'unconditionalising'
this code. (i.e. the allocation of an extra 328 bytes per process).
Signal handling information remains in the U area until such a time as
it's reference count would be incremented to > 1. At that point a new
struct is malloc'd and maintained in KVM so that it can be shared between
the processes (threads) using it.
A function to check the reference count and move the struct back to the U
area when it drops back to 1 is also supplied. Signal information is
therefore now swapable for all processes that are not sharing that
information with other processes. THis should addres the concerns raised
by Garrett and others.
Submitted by: "Richard Seaman, Jr." <dick@tar.com>
downward growing stacks more general.
Add (but don't activate) code to use the new stack facility
when running threads, (specifically the linux threads support).
This allows people to use both linux compiled linuxthreads, and also the
native FreeBSD linux-threads port.
The code is conditional on VM_STACK. Not using this will
produce the old heavily tested system.
Submitted by: Richard Seaman <dick@tar.com>
