- NetBSD Manual Pages
UVM_KM(9) NetBSD Kernel Developer's Manual UVM_KM(9)
Powered by man-cgi (2021-06-01).
Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
uvm_km -- raw kernel memory or address space allocator
uvm_km_alloc(struct vm_map *map, vsize_t size, vsize_t align,
uvm_km_free(struct vm_map *map, vaddr_t addr, vsize_t size,
struct vm_map *
uvm_km_suballoc(struct vm_map *map, vaddr_t *min, vaddr_t *max,
vsize_t size, int flags, bool fixed, struct vm_map *submap);
The UVM facility for allocation of kernel memory or address space in
pages. Both wired and pageable memory can be allocated by this facility,
as well as kernel address space. Note that this is a raw allocator. For
general purpose memory allocation, kmem(9) interface should be used.
uvm_km_alloc() allocates a contiguous range of size bytes of kernel mem-
ory in map map and returns the virtual address of the range, or returns
zero on failure. The first address of the allocated memory range will be
aligned according to the align argument (specify 0 if no alignment is
necessary). The alignment must be a multiple of page size. The flags is
a bitwise inclusive OR of the allocation type and operation flags.
The allocation type should be one of:
UVM_KMF_WIRED Wired memory.
UVM_KMF_PAGEABLE Demand-paged zero-filled memory.
UVM_KMF_VAONLY Virtual address only. No physical pages are mapped in
the allocated region. If necessary, it is the caller's
responsibility to enter page mappings. It is also the
caller's responsibility to clean up the mappings before
freeing the address range.
The following operation flags are available:
UVM_KMF_CANFAIL Can fail even if UVM_KMF_NOWAIT is not specified and
UVM_KMF_WAITVA is specified.
UVM_KMF_ZERO Request zero-filled memory. Only supported for
UVM_KMF_WIRED. Should not be used with other types.
UVM_KMF_EXEC Request memory with executable rights.
UVM_KMF_TRYLOCK Fail if cannot lock the map without sleeping.
UVM_KMF_NOWAIT Fail immediately if no memory is available.
UVM_KMF_WAITVA Sleep to wait for the virtual address resources if
If neither UVM_KMF_NOWAIT nor UVM_KMF_CANFAIL are specified and
UVM_KMF_WAITVA is specified, uvm_km_alloc() will never fail, but rather
sleep indefinitely until the allocation succeeds.
Pageability of the pages allocated with UVM_KMF_PAGEABLE can be changed
by uvm_map_pageable(). In that case, the entire range must be changed
atomically. Changing a part of the range is not supported.
uvm_km_free() frees the memory range allocated by uvm_km_alloc(). addr
must be an address returned by uvm_km_alloc(). map and size must be the
same as the ones used for the corresponding uvm_km_alloc(). flags must
be the allocation type used for the corresponding uvm_km_alloc(). Note
that uvm_km_free() is the only way to free memory ranges allocated by
uvm_km_alloc(). uvm_unmap() must not be used.
uvm_km_suballoc() allocates submap from map, creating a new map if submap
is NULL. The addresses of the submap can be specified explicitly by set-
ting the fixed argument to true, which causes the min argument to specify
the beginning of the address in the submap. If fixed is false, any
address of size size will be allocated from map and the start and end
addresses returned in min and max. The flags are used to initialize the
created submap. The following flags can be set:
VM_MAP_PAGEABLE Entries in the map may be paged out.
VM_MAP_INTRSAFE Map should be interrupt-safe.
VM_MAP_TOPDOWN A top-down mapping should be arranged.
kmem(9), pmap(9), pool_cache(9), uvm(9), uvm_map(9), vmem(9)
UVM and uvm_km first appeared in NetBSD 1.4.
NetBSD 8.1 August 15, 2015 NetBSD 8.1