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.\" $FreeBSD$
.\"
.Dd January 28, 2012
.Dt VM_PAGE_ALLOC 9
.Os
.Sh NAME
.Nm vm_page_alloc
.Nd "allocate a page for a"
.Vt vm_object
.Sh SYNOPSIS
.In sys/param.h
.In vm/vm.h
.In vm/vm_page.h
.Ft vm_page_t
.Fn vm_page_alloc "vm_object_t object" "vm_pindex_t pindex" "int req"
.Sh DESCRIPTION
The
.Fn vm_page_alloc
function allocates a page at
.Fa pindex
within
.Fa object .
It is assumed that a page has not already been allocated at
.Fa pindex .
The page returned is inserted into the object, unless
.Dv VM_ALLOC_NOOBJ
is specified in the
.Fa req .
The page may exist in the vm object cache, in which case it will
be reactivated instead, moving from the cache into the object page list.
.Pp
.Fn vm_page_alloc
will not sleep.
.Pp
Its arguments are:
.Bl -tag -width ".Fa object"
.It Fa object
The VM object to allocate the page for.
The
.Fa object
must be locked if
.Dv VM_ALLOC_NOOBJ
is not specified.
.It Fa pindex
The index into the object at which the page should be inserted.
.It Fa req
The bitwise-inclusive OR of a class and any optional flags indicating
how the page should be allocated.
.Pp
Exactly one of the following classes must be specified:
.Bl -tag -width ".Dv VM_ALLOC_INTERRUPT"
.It Dv VM_ALLOC_NORMAL
The page should be allocated with no special treatment.
.It Dv VM_ALLOC_SYSTEM
The page can be allocated if the cache is empty and the free
page count is above the interrupt reserved water mark.
This flag should be used only when the system really needs the page.
.It Dv VM_ALLOC_INTERRUPT
.Fn vm_page_alloc
is being called during an interrupt.
A page will be returned successfully if the free page count is greater
than zero.
.El
.Pp
The optional flags are:
.Bl -tag -width ".Dv VM_ALLOC_IFNOTCACHED"
.It Dv VM_ALLOC_NOBUSY
The returned page will not have the
.Dv VPO_BUSY
flag set.
.It Dv VM_ALLOC_NODUMP
The returned page will not be included in any kernel core dumps
regardless of whether or not it is mapped in to KVA.
.It Dv VM_ALLOC_NOOBJ
Do not associate the allocated page with a vm object.
The
.Fa object
argument is ignored.
.It Dv VM_ALLOC_IFCACHED
Allocate the page only if it is cached.
Otherwise, return
.Dv NULL .
.It Dv VM_ALLOC_IFNOTCACHED
Only allocate the page if it is not cached in the
.Fa object .
If the page at the specified
.Fa pindex
is cached, NULL is returned instead.
.It Dv VM_ALLOC_WIRED
The returned page will be wired.
.It Dv VM_ALLOC_ZERO
Indicate a preference for a pre-zeroed page.
There is no guarantee that the returned page will be zeroed, but it
will have the
.Dv PG_ZERO
flag set if it is zeroed.
.El
.El
.Sh RETURN VALUES
The
.Vt vm_page_t
that was allocated is returned if successful; otherwise,
.Dv NULL
is returned.
.Sh NOTES
The pager process is always upgraded to
.Dv VM_ALLOC_SYSTEM
unless
.Dv VM_ALLOC_INTERRUPT
is set.
.Sh AUTHORS
This manual page was written by
.An Chad David Aq davidc@acns.ab.ca .