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.\" $FreeBSD$
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.Dd February 27, 2010
.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 page_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 page_req ,
but is not inserted into a pmap.
The page may exists 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 page_req"
.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 page_req
A flag indicating how the page should be allocated.
.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 queue is empty and the free
page count is above the interrupt reserved water mark.
If
.Dv VM_ALLOC_INTERRUPT
is set, the page can be allocated as long as the free page count is
greater than zero.
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 and therefore the cache cannot
be accessed.
The page will only be returned successfully if the free count is greater
than zero.
.It Dv VM_ALLOC_ZERO
Indicate a preference for a pre-zeroed page.
There is no guarantee that the page thus returned will be zeroed, but
it will be marked by
.Dv PG_ZERO
flag if it is zeroed.
.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_NOBUSY
The page returned will not be busied.
.It Dv VM_ALLOC_WIRED
The returned page is wired.
.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.
.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 .