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NAME

     vm_page_alloc - allocate a page for a vm_object

SYNOPSIS

     #include <sys/param.h>
     #include <vm/vm.h>
     #include <vm/vm_page.h>

     vm_page_t
     vm_page_alloc(vm_object_t object, vm_pindex_t pindex, int page_req);

DESCRIPTION

     The vm_page_alloc() function allocates a page at pindex within object.
     It is assumed that a page has not already been allocated at pindex.  The
     page returned is inserted into the object, but is not inserted into the
     pmap.

     vm_page_alloc() will not block.

     Its arguments are:

     object    The VM object to allocate the page for.

     pindex    The index into the object at which the page should be inserted.

     page_req  A flag indicating how the page should be allocated.

               VM_ALLOC_NORMAL     The page should be allocated with no
                                   special treatment.

               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 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.

               VM_ALLOC_INTERRUPT  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.

               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 as such.

               VM_ALLOC_NOOBJ      The page is associated with an unmanaged
                                   memory region, that is, there is no backing
                                   VM object.  This is typically used to
                                   allocate pages within the kernel virtual
                                   address space.

RETURN VALUES

     The vm_page_t that was allocated is returned if successful; otherwise,
     NULL is returned.

NOTES

     The pager process is always upgraded to VM_ALLOC_SYSTEM unless
     VM_ALLOC_INTERRUPT is set.

AUTHORS

     This manual page was written by Chad David 〈davidc@acns.ab.ca〉.