FreeBSD-5.3/share/man/man9/jumbo.9

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.\" $FreeBSD: src/share/man/man9/jumbo.9,v 1.2 2002/12/12 14:17:24 ru Exp $
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.Dd June 23, 2002
.Dt JUMBO 9
.Os
.Sh NAME
.Nm jumbo ,
.Nm jumbo_vm_init ,
.Nm jumbo_pg_alloc ,
.Nm jumbo_pg_free ,
.Nm jumbo_freem ,
.Nm jumbo_pg_steal ,
.Nm jumbo_phys_to_kva
.Nd kernel interface for allocating and freeing page-sized disposable buffers
.Sh SYNOPSIS
.In sys/jumbo.h
.Ft int
.Fn jumbo_vm_init void
.Ft vm_page_t
.Fn jumbo_pg_alloc void
.Ft void
.Fn jumbo_pg_free "vm_offset_t addr"
.Ft void
.Fn jumbo_freem "caddr_t addr" "void *args"
.Ft void
.Fn jumbo_pg_steal "vm_page_t pg"
.Ft caddr_t
.Fn jumbo_phys_to_kva "vm_offset_t pa"
.Sh DESCRIPTION
The
.Nm
buffer facility is designed for allocating disposable page-sized
buffers.
Buffers allocated via this facility can either be returned or not.
This facility is primarily intended for use with network adapters
that have MTUs of a page or greater size.
The buffers will normally be disposed of by the
.Xr zero_copy 9
receive code.
.Pp
.Fn jumbo_vm_init
initializes the pool of KVA the
.Nm
code needs to operate and does some
other initialization to prepare the subsystem for operation.
This routine only needs to be called once.
Calling it multiple times will have no effect.
It is recommended that this initialization routine be called in a
device driver attach routine, so that resources are not allocated if the
.Nm
subsystem will not end up being used.
.Fn jumbo_vm_init
returns 1 upon successful completion, and 0 upon failure.
.Pp
.Fn jumbo_pg_alloc
allocates a physical page and assigns a piece of KVA from the
.Nm
KVA pool.
It returns the allocated page if successful, and
.Dv NULL
in the case of failure.
.Pp
.Fn jumbo_pg_free
frees a page allocated by
.Fn jumbo_pg_alloc .
It takes the address of the memory in question as an argument.
This routine will normally be used in cases where the allocated
.Nm
page cannot be used for some reason.
The normal free path is via
.Fn jumbo_freem .
.Pp
.Fn jumbo_freem
is the routine that should be given as the external free routine when an
external
.Vt mbuf
is allocated using pages from the
.Nm
allocator.
It takes the virtual address of the page in question, and
ignores the second argument.
.Pp
.Fn jumbo_pg_steal
.Dq steals
a page and recycles its KVA space.
.Pp
.Fn jumbo_phys_to_kva
translates the physical address of a
.Nm
allocated page to the proper kernel virtual address.
.Sh SEE ALSO
.Xr ti 4 ,
.Xr zero_copy 9
.Sh HISTORY
The
.Nm
allocator is primarily based on a page allocator system originally written
by
.An Andrew Gallatin Aq gallatin@FreeBSD.org
as part of a set of zero copy patches for the
.Xr ti 4
driver.
The allocator was taken out of the
.Xr ti 4
driver, cleaned up and ported to the new
.Xr mutex 9
interface by
.An Kenneth Merry Aq ken@FreeBSD.org .
.Pp
The
.Nm
allocator first appeared in
.Fx 5.0 ,
and has existed in patch form since at least 1999.
.Sh AUTHORS
.An Andrew Gallatin Aq gallatin@FreeBSD.org
.An Kenneth Merry Aq ken@FreeBSD.org
.Sh BUGS
There is currently a static number of KVA pages allocated by the
.Nm
allocator, with no real provision for increasing the number of pages
allocated should demand exceed supply.
.Pp
The
.Fn jumbo_pg_steal
function is not currently used anywhere.