contig_malloc(9r)contig_malloc(9r)NAMEcontig_malloc - General: Allocates physically contiguous memory
SYNOPSIS
#include <sys/malloc.h>
void * contig_malloc(
u_long size,
u_long alignment,
u_long addrlimit,
int type,
int flag );
ARGUMENTS
Specifies the size of the memory (in bytes) to allocate. Specifies the
alignment of the memory to be allocated. For example, for a 256-byte
alignment, you should pass the value 256. A 0 (zero) value means there
is no alignment requirement. Specifies that the address of all the
allocated memory should be less than or equal to this address. A 0
(zero) value means that there is no address limit requirement. Speci‐
fies the purpose for which the memory is being allocated (or freed).
The memory type constants are defined in the file
/usr/sys/include/sys/malloc.h. Examples of memory type constants are
M_DEVBUF (device driver memory), M_KTABLE (kernel table memory),
M_RTABLE (routing tables memory), M_EXEMPT (exempt memory), and so
forth. Specifies one of the following flags defined in
/usr/sys/include/sys/malloc.h: Signifies that contig_malloc should zero
the allocated memory. Signifies that contig_malloc can block. Signi‐
fies that contig_malloc cannot block.
DESCRIPTION
The contig_malloc routine allocates physically contiguous memory during
the boot process (before single-user mode). The routine carves out an
area of physically contiguous memory from a contiguous memory buffer
and allocates memory from this buffer with proper alignment. The call
to contig_malloc is the same for statically or dynamically configured
kernel modules. However, the point or points in time in which the stat‐
ically or dynamically configured kernel module requests the memory dif‐
fer.
A statically configured kernel module typically needs to call con‐
tig_malloc only before single-user mode. In this case, contig_malloc
obtains the memory from the contiguous memory buffer. When a stati‐
cally configured kernel module frees this physically contiguous memory
(by calling the contig_free routine), the memory is returned to the
virtual memory subsystem.
A dynamically configured kernel module typically needs physically con‐
tiguous memory after single-user mode. As stated previously, con‐
tig_malloc carves out an area of physically contiguous memory from a
contiguous memory buffer before single-user mode. Thus, this memory
would not be available to the dynamically configured kernel module
after single-user mode. To solve this problem, a dynamically configured
kernel module calls contig_malloc by defining the CMA_Option attribute
in the sysconfigtab file fragment.
The cma_dd subsystem calls contig_malloc on behalf of dynamically con‐
figured kernel modules and obtains the memory allocation size (and
other information) from the CMA_Option attribute field. In this case,
contig_malloc allocates physically contiguous memory from the contigu‐
ous memory buffer and places it in a saved memory pool. When a dynami‐
cally configured kernel module needs to call contig_malloc after sin‐
gle-user mode, the physically contiguous memory comes from this saved
memory pool. When a dynamically configured kernel module frees this
physically contiguous memory (by calling the contig_free routine), the
memory is returned to the saved memory pool (not to the virtual memory
subsystem). Thus, this physically contiguous memory is available to the
dynamically configured kernel module upon subsequent reload requests
that occur after single-user mode.
An exempt region of memory can be allocated through the use of con‐
tig_malloc. This can be done in a pseudo device driver in the postcon‐
fig_callback routine. ( Exempt memory is memory managed by UNIX, but
not included in testing and core dumps.)
Allocating exempt memory follows the same guidelines that a normal con‐
tiguous malloc would follow except: The type field would be M_EXEMPT,
trackable with vmstat -M. The addrlimit field has been overloaded to
allow specification of a starting address. (The starting address is a
physical address.) If an address is specified and not available, the
call will return a failure. Use of the alignment parameter is useless
in this case. A call would look like:
addr = contig_malloc(size, alignment, start_addr, M_EXEMPT,
flags);
Where: Indicates the allocation size in bytes (this must be
specified) Indicates the allocation alignment if no start_addr
or zero to default to base page size. Indicates the base start
address to allocate from or 0 if no preference.
This can also be done using the sysconfigtab entry. Under cma_dd:
CMA_option = size - 0x40000, alignment - 0, Addrlimit - 0, Type - 143,
Flag - 1
The arguments are the same as in the example call. 143 corresponds to
what is in malloc.h. Note that the returned addr will have the low bit
set if there is a bad page in the allocated region.
RETURN VALUES
Upon successful completion, contig_malloc returns a pointer to the
allocated memory. If contig_malloc cannot allocate the requested mem‐
ory, it returns a null pointer.
SEE ALSO
Routines: contig_free(9r)contig_malloc(9r)
