http://mail-index.netbsd.org/source-changes/2003/05/08/0068.html
There were some side-effects that I didn't anticipate, and fixing them
is proving to be more difficult than I thought, do just eject for now.
Maybe one day we can look at this again.
Fixes PR kern/21517.
space is advertised to UVM by making virtual_avail and virtual_end
first-class exported variables by UVM. Machine-dependent code is
responsible for initializing them before main() is called. Anything
that steals KVA must adjust these variables accordingly.
This reduces the number of instances of this info from 3 to 1, and
simplifies the pmap(9) interface by removing the pmap_virtual_space()
function call, and removing two arguments from pmap_steal_memory().
This also eliminates some kludges such as having to burn kernel_map
entries on space used by the kernel and stolen KVA.
This also eliminates use of VM_{MIN,MAX}_KERNEL_ADDRESS from MI code,
this giving MD code greater flexibility over the bounds of the managed
kernel virtual address space if a given port's specific platforms can
vary in this regard (this is especially true of the evb* ports).
- remove special treatment of pager_map mappings in pmaps. this is
required now, since I've removed the globals that expose the address range.
pager_map now uses pmap_kenter_pa() instead of pmap_enter(), so there's
no longer any need to special-case it.
- eliminate struct uvm_vnode by moving its fields into struct vnode.
- rewrite the pageout path. the pager is now responsible for handling the
high-level requests instead of only getting control after a bunch of work
has already been done on its behalf. this will allow us to UBCify LFS,
which needs tighter control over its pages than other filesystems do.
writing a page to disk no longer requires making it read-only, which
allows us to write wired pages without causing all kinds of havoc.
- use a new PG_PAGEOUT flag to indicate that a page should be freed
on behalf of the pagedaemon when it's unlocked. this flag is very similar
to PG_RELEASED, but unlike PG_RELEASED, PG_PAGEOUT can be cleared if the
pageout fails due to eg. an indirect-block buffer being locked.
this allows us to remove the "version" field from struct vm_page,
and together with shrinking "loan_count" from 32 bits to 16,
struct vm_page is now 4 bytes smaller.
- no longer use PG_RELEASED for swap-backed pages. if the page is busy
because it's being paged out, we can't release the swap slot to be
reallocated until that write is complete, but unlike with vnodes we
don't keep a count of in-progress writes so there's no good way to
know when the write is done. instead, when we need to free a busy
swap-backed page, just sleep until we can get it busy ourselves.
- implement a fast-path for extending writes which allows us to avoid
zeroing new pages. this substantially reduces cpu usage.
- encapsulate the data used by the genfs code in a struct genfs_node,
which must be the first element of the filesystem-specific vnode data
for filesystems which use genfs_{get,put}pages().
- eliminate many of the UVM pagerops, since they aren't needed anymore
now that the pager "put" operation is a higher-level operation.
- enhance the genfs code to allow NFS to use the genfs_{get,put}pages
instead of a modified copy.
- clean up struct vnode by removing all the fields that used to be used by
the vfs_cluster.c code (which we don't use anymore with UBC).
- remove kmem_object and mb_object since they were useless.
instead of allocating pages to these objects, we now just allocate
pages with no object. such pages are mapped in the kernel until they
are freed, so we can use the mapping to find the page to free it.
this allows us to remove splvm() protection in several places.
The sum of all these changes improves write throughput on my
decstation 5000/200 to within 1% of the rate of NetBSD 1.5
and reduces the elapsed time for "make release" of a NetBSD 1.5
source tree on my 128MB pc to 10% less than a 1.5 kernel took.
provides us more flexibility with pageq-locked fields, and clarifies the
locking semantics for platforms which cannot address shorts.
From Ross Harvey.
dynamically re-coloring pages; as machine-dependent code discovers
the size of the system's caches, it may call uvm_page_recolor() with
the new number of colors to use. If the new mumber of colors is
smaller (or equal to) the current number of colors, then uvm_page_recolor()
is a no-op.
The system defaults to one bucket if machine-dependent code does not
initialize uvmexp.ncolors before uvm_page_init() is called.
Note that the number of color bins should be initialized to something
reasonable as early as possible -- for many early memory allocations,
we live with the consequences of the page choice for the lifetime of
the boot.
each vm_page structure. Add a VM_MDPAGE_INIT() macro to init this
data when pages are initialized by UVM. These macros are mandatory,
but ports may #define them to nothing if they are not needed/used.
This deprecates struct pmap_physseg. As a transitional measure,
allow a port to #define PMAP_PHYSSEG so that it can continue to
use it until its pmap is converted to use VM_MDPAGE_MEMBERS.
Use all this stuff to eliminate a lot of extra work in the Alpha
pmap module (it's smaller and faster now). Changes to other pmap
modules will follow.
algorithm (Solaris calls this "Bin Hopping").
This implementation currently relies on MD code to define a
constant defining the number of buckets. This will change
reasonably soon (MD code will be able to dynamically size
the bucket array).
<vm/vm_extern.h> merged into <uvm/uvm_extern.h>
<vm/vm_page.h> merged into <uvm/uvm_page.h>
<vm/pmap.h> has become <uvm/uvm_pmap.h>
this leaves just <vm/vm.h> in NetBSD.
- Make page free lists have two actual queues: known-zero pages and
pages with unknown contents.
- Implement uvm_pageidlezero(). This function attempts to zero up to
the target number of pages until the target has been reached (currently
target is `all free pages') or until whichqs becomes non-zero (indicating
that a process is ready to run).
- Define a new hook for the pmap module for pre-zero'ing pages. This is
used to zero the pages using uncached access. This allows us to zero
as many pages as we want without polluting the cache.
In order to use this feature, each platform must add the appropropriate
glue in their idle loop.
Add a new type voff_t (defined as a synonym for off_t) to describe offsets
into uvm objects, and update the appropriate interfaces to use it, the
most visible effect being the ability to mmap() file offsets beyond
the range of a vaddr_t.
Originally by Chuck Silvers; blame me for problems caused by merging this
into non-UBC.
level directly, instead of making the caller wrap the calls in
splimp()/splx().
- Add a comment documenting that interrupts that cause memory allocation
must be blocked while the free page queue is locked.
Since interrupts must be blocked while this lock is asserted, tying them
together like this helps to prevent mistakes.
default free list, and 0 - N additional free list, in order of descending
priority.
A new page allocation function, uvm_pagealloc_strat(), has been added,
providing three page allocation strategies:
- normal: high -> low priority free list walk, taking the
page off the first free list that has one.
- only: attempt to allocate a page only from the specified free
list, failing if that free list has none available.
- fallback: if `only' fails, fall back on `normal'.
uvm_pagealloc(...) is provided for normal use (and is a synonym for
uvm_pagealloc_strat(..., UVM_PGA_STRAT_NORMAL, 0); the free list argument
is ignored for the `normal' case).
uvm_page_physload() now specified which free list the pages will be
loaded onto. This means that some platforms which have multiple physical
memory segments may define additional vm_physsegs if they wish to break
individual physical segments into differing priorities.
Machine-dependent code must define _at least_ the following constants
in <machine/vmparam.h>:
VM_NFREELIST: the number of free lists the system will have
VM_FREELIST_DEFAULT: the default freelist (should always be 0,
but is defined in machdep code so that it's with all of the
other free list-related constants).
Additional free list names may be defined by machine-dependent code, but
they will only be used by machine-dependent code (e.g. for loading the
vm_physsegs).
UVM was written by chuck cranor <chuck@maria.wustl.edu>, with some
minor portions derived from the old Mach code. i provided some help
getting swap and paging working, and other bug fixes/ideas. chuck
silvers <chuq@chuq.com> also provided some other fixes.
this is the UVM kernel code portion.
this will be KNF'd shortly. :-)
thorpej