freebsd-nq/share/man/man9/contigmalloc.9

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.Dd January 29, 2015
.Dt CONTIGMALLOC 9
.Os
.Sh NAME
.Nm contigmalloc , contigfree
.Nd manage contiguous kernel physical memory
.Sh SYNOPSIS
.In sys/types.h
.In sys/malloc.h
.Ft "void *"
.Fo contigmalloc
.Fa "unsigned long size"
.Fa "struct malloc_type *type"
.Fa "int flags"
.Fa "vm_paddr_t low"
.Fa "vm_paddr_t high"
.Fa "unsigned long alignment"
.Fa "vm_paddr_t boundary"
.Fc
.Ft void
.Fo contigfree
.Fa "void *addr"
.Fa "unsigned long size"
.Fa "struct malloc_type *type"
.Fc
.Sh DESCRIPTION
The
.Fn contigmalloc
function allocates
.Fa size
bytes of contiguous physical memory that is aligned to
.Fa alignment
bytes, and which does not cross a boundary of
.Fa boundary
bytes.
If successful, the allocation will reside between physical addresses
.Fa low
and
.Fa high .
The returned pointer points to a wired kernel virtual
address range of
.Fa size
bytes allocated from the kernel virtual address (KVA) map.
.Pp
The
.Fa flags
parameter modifies
.Fn contigmalloc Ns 's
behaviour as follows:
.Bl -tag -width indent
.It Dv M_ZERO
Causes the allocated physical memory to be zero filled.
.It Dv M_NOWAIT
Causes
.Fn contigmalloc
to return
.Dv NULL
if the request cannot be immediately fulfilled due to resource shortage.
.El
.Pp
Other flags (if present) are ignored.
.Pp
The
.Fn contigfree
function deallocates memory allocated by a previous call to
.Fn contigmalloc .
.Sh IMPLEMENTATION NOTES
The
.Fn contigmalloc
function does not sleep waiting for memory resources to be freed up,
but instead actively reclaims pages before giving up.
However, unless
.Dv M_NOWAIT
is specified, it may select a page for reclamation that must first be
written to backing storage, causing it to sleep.
.Pp
The
.Fn contigfree
function does not accept
.Dv NULL
as an address input, unlike
.Xr free 9 .
.Sh RETURN VALUES
The
.Fn contigmalloc
function returns a kernel virtual address if allocation succeeds,
or
.Dv NULL
otherwise.
.Sh EXAMPLES
.Bd -literal
void *p;
p = contigmalloc(8192, M_DEVBUF, M_ZERO, 0, (1L << 22),
    32 * 1024, 1024 * 1024);
.Ed
.Pp
Ask for 8192 bytes of zero-filled memory residing between physical
address 0 and 4194303 inclusive, aligned to a 32K boundary and not
crossing a 1M address boundary.
.Sh DIAGNOSTICS
The
.Fn contigmalloc
function will panic if
.Fa size
is zero, or if
.Fa alignment
or
.Fa boundary
is not a power of two.
.Sh SEE ALSO
.Xr malloc 9 ,
.Xr memguard 9