path: root/share/man/man9/uvm.9

.\"	$OpenBSD: uvm.9,v 1.51 2014/01/21 03:15:46 schwarze Exp $
.\"	$NetBSD: uvm.9,v 1.14 2000/06/29 06:08:44 mrg Exp $
.\"
.\" Copyright (c) 1998 Matthew R. Green
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.\" XXX this manual sets nS to 1 or 0 in the description, to obtain
.\" synopsis-like function prototypes.  any better way?
.\"
.Dd $Mdocdate: January 21 2014 $
.Dt UVM 9
.Os
.Sh NAME
.Nm uvm
.Nd virtual memory system external interface
.Sh SYNOPSIS
.In sys/param.h
.In uvm/uvm.h
.Sh DESCRIPTION
The UVM virtual memory system manages access to the computer's memory
resources.
User processes and the kernel access these resources through
UVM's external interface.
UVM's external interface includes functions that:
.Pp
.Bl -hyphen -compact
.It
initialise UVM subsystems
.It
manage virtual address spaces
.It
resolve page faults
.It
memory map files and devices
.It
perform uio-based I/O to virtual memory
.It
allocate and free kernel virtual memory
.It
allocate and free physical memory
.El
.Pp
In addition to exporting these services, UVM has two kernel-level processes:
pagedaemon and swapper.
The pagedaemon process sleeps until physical memory becomes scarce.
When that happens, pagedaemon is awoken.
It scans physical memory, paging out and freeing memory that has not been
recently used.
The swapper process swaps in runnable processes that are currently swapped out,
if there is room.
.Pp
UVM has a machine independent and a machine dependent layer.
See
.Xr pmap 9
for the machine dependent layer.
.Sh INITIALISATION
.nr nS 1
.Ft void
.Fn uvm_init "void"
.Ft void
.Fn uvm_init_limits "struct proc *p"
.Ft void
.Fn uvm_setpagesize "void"
.Ft void
.Fn uvm_swap_init "void"
.nr nS 0
.Pp
The
.Fn uvm_init
function sets up the UVM system at system boot time, after the
copyright has been printed.
It initialises global state, the page, map, kernel virtual memory state,
machine-dependent physical map, kernel memory allocator,
pager and anonymous memory subsystems, and then enables
paging of kernel objects.
.Fn uvm_init
must be called after machine-dependent code has registered some free RAM
with the
.Fn uvm_page_physload
function.
.Pp
The
.Fn uvm_init_limits
function initialises process limits for the named process.
This is for use by the system startup for process zero, before any other
processes are created.
.Pp
The
.Fn uvm_setpagesize
function initialises the uvmexp members pagesize (if not already done by
machine-dependent code), pageshift and pagemask.
It should be called by machine-dependent code early in the
.Xr pmap_init 9
call.
.Pp
The
.Fn uvm_swap_init
function initialises the swap subsystem.
.Sh VIRTUAL ADDRESS SPACE MANAGEMENT
.nr nS 1
.Ft int
.Fn uvm_map "vm_map_t map" "vaddr_t *startp" "vsize_t size" "struct uvm_object *uobj" "voff_t uoffset" "vsize_t alignment" "uvm_flag_t flags"
.Ft int
.Fn uvm_map_pageable "vm_map_t map" "vaddr_t start" "vaddr_t end" "boolean_t new_pageable" "int lockflags"
.Ft int
.Fn uvm_map_pageable_all "vm_map_t map" "int flags" "vsize_t limit"
.Ft boolean_t
.Fn uvm_map_checkprot "vm_map_t map" "vaddr_t start" "vaddr_t end" "vm_prot_t protection"
.Ft int
.Fn uvm_map_protect "vm_map_t map" "vaddr_t start" "vaddr_t end" "vm_prot_t new_prot" "boolean_t set_max"
.Ft int
.Fn uvm_deallocate "vm_map_t map" "vaddr_t start" "vsize_t size"
.Ft struct vmspace *
.Fn uvmspace_alloc "vaddr_t min" "vaddr_t max" "boolean_t pageable" "boolean_t remove_holes"
.Ft void
.Fn uvmspace_exec "struct proc *p" "vaddr_t start" "vaddr_t end"
.Ft struct vmspace *
.Fn uvmspace_fork "struct vmspace *vm"
.Ft void
.Fn uvmspace_free "struct vmspace *vm1"
.Ft void
.Fn uvmspace_share "struct proc *p1" "struct proc *p2"
.Ft int
.Fn UVM_MAPFLAG "vm_prot_t prot" "vm_prot_t maxprot" "vm_inherit_t inh" "int advice" "int flags"
.nr nS 0
.Pp
The
.Fn uvm_map
function establishes a valid mapping in map
.Fa map ,
which must be unlocked.
The new mapping has size
.Fa size ,
which must be in
.Dv PAGE_SIZE
units.
If
.Fa alignment
is non-zero, it describes the required alignment of the list, in
power-of-two notation.
The
.Fa uobj
and
.Fa uoffset
arguments can have four meanings.
When
.Fa uobj
is
.Dv NULL
and
.Fa uoffset
is
.Dv UVM_UNKNOWN_OFFSET ,
.Fn uvm_map
does not use the machine-dependent
.Dv PMAP_PREFER
function.
If
.Fa uoffset
is any other value, it is used as the hint to
.Dv PMAP_PREFER .
When
.Fa uobj
is not
.Dv NULL
and
.Fa uoffset
is
.Dv UVM_UNKNOWN_OFFSET ,
.Fn uvm_map
finds the offset based upon the virtual address, passed as
.Fa startp .
If
.Fa uoffset
is any other value, we are doing a normal mapping at this offset.
The start address of the map will be returned in
.Fa startp .
.Pp
.Fa flags
passed to
.Fn uvm_map
are typically created using the
.Fn UVM_MAPFLAG
macro, which uses the following values.
The
.Fa prot
and
.Fa maxprot
can take the following values:
.Bd -literal
#define UVM_PROT_MASK   0x07    /* protection mask */
#define UVM_PROT_NONE   0x00    /* protection none */
#define UVM_PROT_ALL    0x07    /* everything */
#define UVM_PROT_READ   0x01    /* read */
#define UVM_PROT_WRITE  0x02    /* write */
#define UVM_PROT_EXEC   0x04    /* exec */
#define UVM_PROT_R      0x01    /* read */
#define UVM_PROT_W      0x02    /* write */
#define UVM_PROT_RW     0x03    /* read-write */
#define UVM_PROT_X      0x04    /* exec */
#define UVM_PROT_RX     0x05    /* read-exec */
#define UVM_PROT_WX     0x06    /* write-exec */
#define UVM_PROT_RWX    0x07    /* read-write-exec */
.Ed
.Pp
The values that
.Fa inh
can take are:
.Bd -literal
#define UVM_INH_MASK    0x30    /* inherit mask */
#define UVM_INH_SHARE   0x00    /* "share" */
#define UVM_INH_COPY    0x10    /* "copy" */
#define UVM_INH_NONE    0x20    /* "none" */
#define UVM_INH_DONATE  0x30    /* "donate" << not used */
.Ed
.Pp
The values that
.Fa advice
can take are:
.Bd -literal
#define UVM_ADV_NORMAL  0x0     /* 'normal' */
#define UVM_ADV_RANDOM  0x1     /* 'random' */
#define UVM_ADV_SEQUENTIAL 0x2  /* 'sequential' */
#define UVM_ADV_MASK    0x7     /* mask */
.Ed
.Pp
The values that
.Fa flags
can take are:
.Bd -literal
#define UVM_FLAG_FIXED   0x010000 /* find space */
#define UVM_FLAG_OVERLAY 0x020000 /* establish overlay */
#define UVM_FLAG_NOMERGE 0x040000 /* don't merge map entries */
#define UVM_FLAG_COPYONW 0x080000 /* set copy_on_write flag */
#define UVM_FLAG_AMAPPAD 0x100000 /* bss: pad amap to reduce malloc() */
#define UVM_FLAG_TRYLOCK 0x200000 /* fail if we can not lock map */
#define UVM_FLAG_HOLE    0x400000 /* no backend */
.Ed
.Pp
The
.Dv UVM_MAPFLAG
macro arguments can be combined with an or operator.
There are several special purpose macros for checking protection combinations,
e.g., the
.Dv UVM_PROT_WX
macro.
There are also some additional macros to extract bits from the flags.
The
.Dv UVM_PROTECTION ,
.Dv UVM_INHERIT ,
.Dv UVM_MAXPROTECTION
and
.Dv UVM_ADVICE
macros return the protection, inheritance, maximum protection and advice,
respectively.
.Fn uvm_map
returns a standard errno.
.Pp
The
.Fn uvm_map_pageable
function changes the pageability of the pages in the range from
.Fa start
to
.Fa end
in map
.Fa map
to
.Fa new_pageable .
The
.Fn uvm_map_pageable_all
function changes the pageability of all mapped regions.
If
.Fa limit
is non-zero and
.Fn pmap_wired_count
is implemented,
.Dv ENOMEM
is returned if the amount of wired pages exceed
.Fa limit .
The map is locked on entry if
.Fa lockflags
contain
.Dv UVM_LK_ENTER ,
and locked on exit if
.Fa lockflags
contain
.Dv UVM_LK_EXIT .
.Fn uvm_map_pageable
and
.Fn uvm_map_pageable_all
return a standard errno.
.Pp
The
.Fn uvm_map_checkprot
function checks the protection of the range from
.Fa start
to
.Fa end
in map
.Fa map
against
.Fa protection .
This returns either
.Dv TRUE
or
.Dv FALSE .
.Pp
The
.Fn uvm_map_protect
function changes the protection
.Fa start
to
.Fa end
in map
.Fa map
to
.Fa new_prot ,
also setting the maximum protection to the region to
.Fa new_prot
if
.Fa set_max
is non-zero.
This function returns a standard errno.
.Pp
The
.Fn uvm_deallocate
function deallocates kernel memory in map
.Fa map
from address
.Fa start
to
.Fa start + size .
.Pp
The
.Fn uvmspace_alloc
function allocates and returns a new address space, with ranges from
.Fa min
to
.Fa max ,
setting the pageability of the address space to
.Fa pageable .
If
.Fa remove_holes
is non-zero, hardware
.Sq holes
in the virtual address space will be removed from the newly allocated
address space.
.Pp
The
.Fn uvmspace_exec
function either reuses the address space of process
.Fa p
if there are no other references to it, or creates
a new one with
.Fn uvmspace_alloc .
The range of valid addresses in the address space is reset to
.Fa start
through
.Fa end .
.Pp
The
.Fn uvmspace_fork
function creates and returns a new address space based upon the
.Fa vm1
address space, typically used when allocating an address space for a
child process.
.Pp
The
.Fn uvmspace_free
function lowers the reference count on the address space
.Fa vm ,
freeing the data structures if there are no other references.
.Pp
The
.Fn uvmspace_share
function causes process
.Fa p2
to share the address space of
.Fa p1 .
.Sh PAGE FAULT HANDLING
.nr nS 1
.Ft int
.Fn uvm_fault "vm_map_t orig_map" "vaddr_t vaddr" "vm_fault_t fault_type" "vm_prot_t access_type"
.nr nS 0
.Pp
The
.Fn uvm_fault
function is the main entry point for faults.
It takes
.Fa orig_map
as the map the fault originated in, a
.Fa vaddr
offset into the map the fault occurred,
.Fa fault_type
describing the type of fault, and
.Fa access_type
describing the type of access requested.
.Fn uvm_fault
returns a standard errno.
.Sh MEMORY MAPPING FILES AND DEVICES
.nr nS 1
.Ft struct uvm_object *
.Fn uvn_attach "void *arg" "vm_prot_t accessprot"
.Ft void
.Fn uvm_vnp_setsize "struct vnode *vp" "voff_t newsize"
.Ft void
.Fn uvm_vnp_sync "struct mount *mp"
.Ft void
.Fn uvm_vnp_terminate "struct vnode *vp"
.Ft boolean_t
.Fn uvm_vnp_uncache "struct vnode *vp"
.nr nS 0
.Pp
The
.Fn uvn_attach
function attaches a UVM object to vnode
.Fa arg ,
creating the object if necessary.
The object is returned.
.Pp
The
.Fn uvm_vnp_setsize
function sets the size of vnode
.Fa vp
to
.Fa newsize .
Caller must hold a reference to the vnode.
If the vnode shrinks, pages no longer used are discarded.
This function will be removed when the file system and VM buffer caches
are merged.
.Pp
The
.Fn uvm_vnp_sync
function flushes dirty vnodes from either the mount point passed in
.Fa mp ,
or all dirty vnodes if
.Fa mp
is
.Dv NULL .
This function will be removed when the file system and VM buffer caches
are merged.
.Pp
The
.Fn uvm_vnp_terminate
function frees all VM resources allocated to vnode
.Fa vp .
If the vnode still has references, it will not be destroyed; however
all future operations using this vnode will fail.
This function will be removed when the file system and VM buffer caches
are merged.
.Pp
The
.Fn uvm_vnp_uncache
function disables vnode
.Fa vp
from persisting when all references are freed.
This function will be removed when the file system and UVM caches
are unified.
Returns true if there is no active vnode.
.Sh VIRTUAL MEMORY I/O
.nr nS 1
.Ft int
.Fn uvm_io "vm_map_t map" "struct uio *uio"
.nr nS 0
.Pp
The
.Fn uvm_io
function performs the I/O described in
.Fa uio
on the memory described in
.Fa map .
.Sh ALLOCATION OF KERNEL MEMORY
.nr nS 1
.Ft vaddr_t
.Fn uvm_km_alloc "vm_map_t map" "vsize_t size"
.Ft vaddr_t
.Fn uvm_km_zalloc "vm_map_t map" "vsize_t size"
.Ft vaddr_t
.Fn uvm_km_alloc1 "vm_map_t map" "vsize_t size" "vsize_t align" "boolean_t zeroit"
.Ft vaddr_t
.Fn uvm_km_kmemalloc "vm_map_t map" "struct uvm_object *obj" "vsize_t size" "int flags"
.Ft vaddr_t
.Fn uvm_km_valloc "vm_map_t map" "vsize_t size"
.Ft vaddr_t
.Fn uvm_km_valloc_wait "vm_map_t map" "vsize_t size"
.Ft struct vm_map *
.Fn uvm_km_suballoc "vm_map_t map" "vaddr_t *min" "vaddr_t *max " "vsize_t size" "int flags" "boolean_t fixed" "vm_map_t submap"
.Ft void
.Fn uvm_km_free "vm_map_t map" "vaddr_t addr" "vsize_t size"
.Ft void
.Fn uvm_km_free_wakeup "vm_map_t map" "vaddr_t addr" "vsize_t size"
.nr nS 0
.Pp
The
.Fn uvm_km_alloc
and
.Fn uvm_km_zalloc
functions allocate
.Fa size
bytes of wired kernel memory in map
.Fa map .
In addition to allocation,
.Fn uvm_km_zalloc
zeros the memory.
Both of these functions are defined as macros in terms of
.Fn uvm_km_alloc1 ,
and should almost always be used in preference to
.Fn uvm_km_alloc1 .
.Pp
The
.Fn uvm_km_alloc1
function allocates and returns
.Fa size
bytes of wired memory in the kernel map aligned to the
.Fa align
boundary, zeroing the memory if the
.Fa zeroit
argument is non-zero.
.Pp
The
.Fn uvm_km_kmemalloc
function allocates and returns
.Fa size
bytes of wired kernel memory into
.Fa obj .
The flags can be any of:
.Bd -literal
#define UVM_KMF_NOWAIT  0x1                     /* matches M_NOWAIT */
#define UVM_KMF_VALLOC  0x2                     /* allocate VA only */
#define UVM_KMF_TRYLOCK UVM_FLAG_TRYLOCK        /* try locking only */
.Ed
.Pp
The
.Dv UVM_KMF_NOWAIT
flag causes
.Fn uvm_km_kmemalloc
to return immediately if no memory is available.
.Dv UVM_KMF_VALLOC
causes no pages to be allocated, only a virtual address.
.Dv UVM_KMF_TRYLOCK
causes
.Fn uvm_km_kmemalloc
to only try and not sleep when locking maps.
.Pp
The
.Fn uvm_km_valloc
and
.Fn uvm_km_valloc_wait
functions return a newly allocated zero-filled address in the kernel map of size
.Fa size .
.Fn uvm_km_valloc_wait
will also wait for kernel memory to become available, if there is a
memory shortage.
.Pp
The
.Fn uvm_km_suballoc
function allocates submap (with the specified
.Fa flags ,
as described above) from
.Fa map ,
creating a new map if
.Fa submap
is
.Dv NULL .
The addresses of the submap can be specified exactly by setting the
.Fa fixed
argument to non-zero, which causes the
.Fa min
argument to specify the beginning of the address in the submap.
If
.Fa fixed
is zero, any address of size
.Fa size
will be allocated from
.Fa map
and the start and end addresses returned in
.Fa min
and
.Fa max .
.Pp
The
.Fn uvm_km_free
and
.Fn uvm_km_free_wakeup
functions free
.Fa size
bytes of memory in the kernel map, starting at address
.Fa addr .
.Fn uvm_km_free_wakeup
calls
.Fn wakeup
on the map before unlocking the map.
.Sh ALLOCATION OF PHYSICAL MEMORY
.nr nS 1
.Ft struct vm_page *
.Fn uvm_pagealloc "struct uvm_object *uobj" "voff_t off" "struct vm_anon *anon" "int flags"
.Ft void
.Fn uvm_pagerealloc "struct vm_page *pg" "struct uvm_object *newobj" "voff_t newoff"
.Ft void
.Fn uvm_pagefree "struct vm_page *pg"
.Ft int
.Fn uvm_pglistalloc "psize_t size" "paddr_t low" "paddr_t high" "paddr_t alignment" "paddr_t boundary" "struct pglist *rlist" "int nsegs" "int flags"
.Ft void
.Fn uvm_pglistfree "struct pglist *list"
.Ft void
.Fn uvm_page_physload "vaddr_t start" "vaddr_t end" "vaddr_t avail_start" "vaddr_t avail_end" "int free_list"
.nr nS 0
.Pp
The
.Fn uvm_pagealloc
function allocates a page of memory at virtual address
.Fa off
in either the object
.Fa uobj
or the anonymous memory
.Fa anon .
Only one of
.Fa anon
and
.Fa uobj
can be non
.Dv NULL .
The
.Fa flags
can be any of:
.Bd -literal
#define UVM_PGA_USERESERVE      0x0001  /* ok to use reserve pages */
#define UVM_PGA_ZERO            0x0002  /* returned page must be zeroed */
.Ed
.Pp
The
.Dv UVM_PGA_USERESERVE
flag means to allocate a page even if that will result in the number of
free pages being lower than
.Dv uvmexp.reserve_pagedaemon
(if the current thread is the pagedaemon) or
.Dv uvmexp.reserve_kernel
(if the current thread is not the pagedaemon).
The
.Dv UVM_PGA_ZERO
flag causes the returned page to be filled with zeroes, either by allocating it
from a pool of pre-zeroed pages or by zeroing it in-line as necessary.
.Pp
The
.Fn uvm_pagerealloc
function reallocates page
.Fa pg
to a new object
.Fa newobj ,
at a new offset
.Fa newoff ,
and returns
.Dv NULL
when no page can be found.
.Pp
The
.Fn uvm_pagefree
function frees the physical page
.Fa pg .
.Pp
The
.Fn uvm_pglistalloc
function allocates a list of pages for size
.Fa size
byte under various constraints.
.Fa low
and
.Fa high
describe the lowest and highest addresses acceptable for the list.
If
.Fa alignment
is non-zero, it describes the required alignment of the list, in
power-of-two notation.
If
.Fa boundary
is non-zero, no segment of the list may cross this power-of-two
boundary, relative to zero.
.Fa nsegs
is the maximum number of physically contiguous segments.
The allocated memory is returned in the
.Fa rlist
list.
The
.Fa flags
can be any of:
.Bd -literal
#define UVM_PLA_WAITOK	0x0001	/* may sleep */
#define UVM_PLA_NOWAIT	0x0002	/* can't sleep */
#define UVM_PLA_ZERO	0x0004	/* zero all pages before returning */
.Ed
.Pp
The
.Dv UVM_PLA_WAITOK
flag means that the function may sleep while trying to allocate the list of
pages (this is currently ignored).
Conversely, the
.Dv UVM_PLA_NOWAIT
flag signifies that the function may not sleep while allocating.
It is an error not to provide one of the above flags.
Optionally, one may also specify the
.Dv UVM_PLA_ZERO
flag to receive zeroed memory in the page list.
.Pp
The
.Fn uvm_pglistfree
function frees the list of pages pointed to by
.Fa list .
.Pp
The
.Fn uvm_page_physload
function loads physical memory segments into VM space on the specified
.Fa free_list .
.Fn uvm_page_physload
must be called at system boot time to set up physical memory management pages.
The arguments describe the
.Fa start
and
.Fa end
of the physical addresses of the segment, and the available start and end
addresses of pages not already in use.
.\" XXX expand on "system boot time"!
.Sh PROCESSES
.nr nS 1
.Ft void
.Fn uvm_pageout "void *arg"
.Ft void
.Fn uvm_scheduler "void"
.Ft void
.Fn uvm_swapin "struct proc *p"
.nr nS 0
.Pp
The
.Fn uvm_pageout
function is the main loop for the page daemon.
The
.Fa arg
argument is ignored.
.Pp
The
.Fn uvm_scheduler
function is the process zero main loop, which is to be called after the
system has finished starting other processes.
.Fn uvm_scheduler
handles the swapping in of runnable, swapped out processes in priority
order.
.Pp
The
.Fn uvm_swapin
function swaps in the named process.
.Sh MISCELLANEOUS FUNCTIONS
.nr nS 1
.Ft struct uvm_object *
.Fn uao_create "vsize_t size" "int flags"
.Ft void
.Fn uao_detach "struct uvm_object *uobj"
.Ft void
.Fn uao_reference "struct uvm_object *uobj"
.Ft boolean_t
.Fn uvm_chgkprot "caddr_t addr" "size_t len" "int rw"
.Ft void
.Fn uvm_kernacc "caddr_t addr" "size_t len" "int rw"
.Ft void
.Fn uvm_vslock "struct proc *p" "caddr_t addr" "size_t len" \
               "vm_prot_t access_type"
.Ft void
.Fn uvm_vsunlock "struct proc *p" "caddr_t addr" "size_t len"
.Ft void
.Fn uvm_meter
.Ft int
.Fn uvm_sysctl "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "void *newp " "size_t newlen" "struct proc *p"
.Ft void
.Fn uvm_fork "struct proc *p1" "struct proc *p2" "boolean_t shared" \
             "void *stack" "size_t stacksize" "void (*func)(void *arg)" \
             "void *arg"
.Ft int
.Fn uvm_grow "struct proc *p" "vaddr_t sp"
.Ft int
.Fn uvm_coredump "struct proc *p" "struct vnode *vp" "struct ucred *cred" "struct core *chdr"
.nr nS 0
.Pp
The
.Fn uao_create ,
.Fn uao_detach
and
.Fn uao_reference
functions operate on anonymous memory objects, such as those used to support
System V shared memory.
.Fn uao_create
returns an object of size
.Fa size
with flags:
.Bd -literal
#define UAO_FLAG_KERNOBJ        0x1     /* create kernel object */
#define UAO_FLAG_KERNSWAP       0x2     /* enable kernel swap */
.Pp
.Ed
which can only be used once each at system boot time.
.Fn uao_reference
creates an additional reference to the named anonymous memory object.
.Fn uao_detach
removes a reference from the named anonymous memory object, destroying
it if removing the last reference.
.Pp
The
.Fn uvm_chgkprot
function changes the protection of kernel memory from
.Fa addr
to
.Fa addr + len
to the value of
.Fa rw .
This is primarily useful for debuggers, for setting breakpoints.
This function is only available with options
.Dv KGDB .
.Pp
The
.Fn uvm_kernacc
function checks the access at address
.Fa addr
to
.Fa addr + len
for
.Fa rw
access, in the kernel address space.
.Pp
The
.Fn uvm_vslock
and
.Fn uvm_vsunlock
functions control the wiring and unwiring of pages for process
.Fa p
from
.Fa addr
to
.Fa addr + len .
The
.Fa access_type
argument of
.Fn uvm_vslock
is passed to
.Fn uvm_fault .
These functions are normally used to wire memory for I/O.
.Pp
The
.Fn uvm_meter
function calculates the load average and wakes up the swapper if necessary.
.Pp
The
.Fn uvm_sysctl
function provides support for the
.Dv CTL_VM
domain of the
.Xr sysctl 3
hierarchy.
.Fn uvm_sysctl
handles the
.Dv VM_LOADAVG ,
.Dv VM_METER
and
.Dv VM_UVMEXP
calls, which return the current load averages, calculates current VM
totals, and returns the uvmexp structure respectively.
The load averages are accessed from userland using the
.Xr getloadavg 3
function.
The uvmexp structure has all global state of the UVM system, and has
the following members:
.Bd -literal
/* vm_page constants */
int pagesize;   /* size of a page (PAGE_SIZE): must be power of 2 */
int pagemask;   /* page mask */
int pageshift;  /* page shift */

/* vm_page counters */
int npages;     /* number of pages we manage */
int free;       /* number of free pages */
int active;     /* number of active pages */
int inactive;   /* number of pages that we free'd but may want back */
int paging;	/* number of pages in the process of being paged out */
int wired;      /* number of wired pages */

int zeropages;		/* number of zero'd pages */
int reserve_pagedaemon; /* number of pages reserved for pagedaemon */
int reserve_kernel;	/* number of pages reserved for kernel */
int anonpages;		/* number of pages used by anon pagers */
int vnodepages;		/* number of pages used by vnode page cache */
int vtextpages;		/* number of pages used by vtext vnodes */

/* pageout params */
int freemin;    /* min number of free pages */
int freetarg;   /* target number of free pages */
int inactarg;   /* target number of inactive pages */
int wiredmax;   /* max number of wired pages */
int anonmin;	/* min threshold for anon pages */
int vtextmin;	/* min threshold for vtext pages */
int vnodemin;	/* min threshold for vnode pages */
int anonminpct;	/* min percent anon pages */
int vtextminpct;/* min percent vtext pages */
int vnodeminpct;/* min percent vnode pages */

/* swap */
int nswapdev;	/* number of configured swap devices in system */
int swpages;	/* number of PAGE_SIZE'ed swap pages */
int swpginuse;	/* number of swap pages in use */
int swpgonly;	/* number of swap pages in use, not also in RAM */
int nswget;	/* number of times fault calls uvm_swap_get() */
int nanon;	/* number total of anon's in system */
int nanonneeded;/* number of anons currently needed */
int nfreeanon;	/* number of free anon's */

/* stat counters */
int faults;		/* page fault count */
int traps;		/* trap count */
int intrs;		/* interrupt count */
int swtch;		/* context switch count */
int softs;		/* software interrupt count */
int syscalls;		/* system calls */
int pageins;		/* pagein operation count */
			/* pageouts are in pdpageouts below */
int swapins;		/* swapins */
int swapouts;		/* swapouts */
int pgswapin;		/* pages swapped in */
int pgswapout;		/* pages swapped out */
int forks;		/* forks */
int forks_ppwait;	/* forks where parent waits */
int forks_sharevm;	/* forks where vmspace is shared */
int pga_zerohit;	/* pagealloc where zero wanted and zero
			   was available */
int pga_zeromiss;	/* pagealloc where zero wanted and zero
			   not available */
int zeroaborts;		/* number of times page zeroing was
			   aborted */

/* fault subcounters */
int fltnoram;	/* number of times fault was out of ram */
int fltnoanon;	/* number of times fault was out of anons */
int fltpgwait;	/* number of times fault had to wait on a page */
int fltpgrele;	/* number of times fault found a released page */
int fltrelck;	/* number of times fault relock called */
int fltrelckok;	/* number of times fault relock is a success */
int fltanget;	/* number of times fault gets anon page */
int fltanretry;	/* number of times fault retrys an anon get */
int fltamcopy;	/* number of times fault clears "needs copy" */
int fltnamap;	/* number of times fault maps a neighbor anon page */
int fltnomap;	/* number of times fault maps a neighbor obj page */
int fltlget;	/* number of times fault does a locked pgo_get */
int fltget;	/* number of times fault does an unlocked get */
int flt_anon;	/* number of times fault anon (case 1a) */
int flt_acow;	/* number of times fault anon cow (case 1b) */
int flt_obj;	/* number of times fault is on object page (2a) */
int flt_prcopy;	/* number of times fault promotes with copy (2b) */
int flt_przero;	/* number of times fault promotes with zerofill (2b) */

/* daemon counters */
int pdwoke;	/* number of times daemon woke up */
int pdrevs;	/* number of times daemon rev'd clock hand */
int pdswout;	/* number of times daemon called for swapout */
int pdfreed;	/* number of pages daemon freed since boot */
int pdscans;	/* number of pages daemon scanned since boot */
int pdanscan;	/* number of anonymous pages scanned by daemon */
int pdobscan;	/* number of object pages scanned by daemon */
int pdreact;	/* number of pages daemon reactivated since boot */
int pdbusy;	/* number of times daemon found a busy page */
int pdpageouts;	/* number of times daemon started a pageout */
int pdpending;	/* number of times daemon got a pending pagout */
int pddeact;	/* number of pages daemon deactivates */
int pdreanon;	/* anon pages reactivated due to min threshold */
int pdrevnode;	/* vnode pages reactivated due to min threshold */
int pdrevtext;	/* vtext pages reactivated due to min threshold */

int fpswtch;	/* FPU context switches */
int kmapent;	/* number of kernel map entries */
.Ed
.Pp
The
.Fn uvm_fork
function forks a virtual address space for process' (old)
.Fa p1
and (new)
.Fa p2 .
If the
.Fa shared
argument is non zero, p1 shares its address space with p2,
otherwise a new address space is created.
The
.Fa stack ,
.Fa stacksize ,
.Fa func
and
.Fa arg
arguments are passed to the machine-dependent
.Fn cpu_fork
function.
The
.Fn uvm_fork
function currently has no return value, and thus cannot fail.
.Pp
The
.Fn uvm_grow
function increases the stack segment of process
.Fa p
to include
.Fa sp .
.Pp
The
.Fn uvm_coredump
function generates a coredump on vnode
.Fa vp
for process
.Fa p
with credentials
.Fa cred
and core header description in
.Fa chdr .
.Sh NOTES
The structure and types whose names begin with
.Dq vm_
were named so UVM could coexist with BSD VM during the early
development stages.
.Sh SEE ALSO
.Xr getloadavg 3 ,
.Xr kvm 3 ,
.Xr sysctl 3 ,
.Xr ddb 4 ,
.Xr options 4 ,
.Xr pmap 9
.Rs
.%A Charles D. Cranor
.%D August 1998
.%C St. Louis, Missouri
.%Q Department of Computer Science, Sever Institute of Technology, Washington University
.%T Design and Implementation of the UVM Virtual Memory System, D.Sc. dissertation
.Re
.Sh HISTORY
The UVM virtual memory system was developed at Washington University in St. Louis.
UVM's roots lie partly in the Mach-based
.Bx 4.4
VM system, the
.Fx
VM system, and the SunOS4 VM system.
UVM's basic structure is based on the
.Bx 4.4
VM system.
UVM's new anonymous memory system is based on the
anonymous memory system found in the SunOS4 VM (as described in papers
published by Sun Microsystems, Inc.).
UVM also includes a number of features
new to
.Bx
including page loanout, map entry passing, simplified
copy-on-write, and clustered anonymous memory pageout.
.Pp
UVM appeared in
.Ox 2.9 .
.Sh AUTHORS
.An -nosplit
.An Charles D. Cranor Aq Mt chuck@ccrc.wustl.edu
designed and implemented UVM.
.Pp
.An Matthew Green Aq Mt mrg@eterna.com.au
wrote the swap-space management code.
.Pp
.An Chuck Silvers Aq Mt chuq@chuq.com
implemented the aobj pager, thus allowing
UVM to support System V shared memory and process swapping.
.Pp
.An Artur Grabowski Aq Mt art@openbsd.org
handled the logistical issues involved with merging UVM into the
.Ox
source tree.
.Sh BUGS
The
.Fn uvm_fork
function should be able to fail in low memory conditions.