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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 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, unless VM_ALLOC_NOOBJ is
     specified in the 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.

     vm_page_alloc() will not sleep.

     Its arguments are:

     object  The VM object to allocate the page for.  The object must be
             locked if VM_ALLOC_NOOBJ is not specified.

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

     req     The bitwise-inclusive OR of a class and any optional flags
             indicating how the page should be allocated.

             Exactly one of the following classes must be specified:

             VM_ALLOC_NORMAL     The page should be allocated with no special
                                 treatment.

             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.

             VM_ALLOC_INTERRUPT  vm_page_alloc() is being called during an
                                 interrupt.  A page will be returned
                                 successfully if the free page count is
                                 greater than zero.

             The optional flags are:

             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 PG_ZERO flag set if it is zeroed.

             VM_ALLOC_NOOBJ        Do not associate the allocated page with a
                                   vm object.  The object argument is ignored.

             VM_ALLOC_NOBUSY       The returned page will not have the
                                   VPO_BUSY flag set.

             VM_ALLOC_WIRED        The returned page will be wired.

             VM_ALLOC_IFCACHED     Allocate the page only if it is cached.
                                   Otherwise, return NULL.

             VM_ALLOC_IFNOTCACHED  Only allocate the page if it is not cached
                                   in the object.  If the page at the
                                   specified pindex is cached, NULL is
                                   returned instead.

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>.