xref: /dflybsd-src/share/man/man9/memory.9 (revision c616d3786462c4bbb32602d276dfb62c4d97ef77)

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.Dd March 23, 2011
.Dt MEMORY 9
.Os
.Sh NAME
.Nm memory
.Nd introduction to kernel memory allocators
.Sh DESCRIPTION
The
.Dx
kernel provides several memory allocators, each with different characteristics
and purposes.
.Ss kmalloc
kmalloc is the primary kernel memory allocator. kmalloc allocates pages from
the kernel address space via
.Xr vm_page_alloc 9
and constructs buffers by slicing allocated pages. Allocations larger than 8 KB
are served directly with pages from the kernel address space. kmalloc tracks
allocation statistics in a malloc_zone structure, which must be declared
before use.
.Pp
kmalloc is implemented as a slab allocator, with per-CPU slab structures. It
may block while attempting to get free pages.
.Pp
For more information, see
.Xr kmalloc 9 .
.Ss Object caches
The object cache is a frontend memory allocator to some backing allocator. It
provides for per-CPU caches of constructed objects, saving time on setup of
allocated structures. The object cache is well-suited to oft-allocated
structures which have relatively complex setup routines.
.Pp
The object cache routines may block allocating cache structures or buffers.
.Pp
For more information, see
.Xr objcache 9 .
.Ss MPIPE
MPIPE is a memory allocator frontend to kmalloc; an MPIPE can be created with
a fixed number of buffers. The MPIPE guarantees that the desired
number of buffers are available and can be allocated without blocking. Beyond
the fixed count, MPIPE calls kmalloc and may block or may fail to allocate.
.Pp
For more information see
.Xr mpipe 9 .
.Ss The Zone Allocator
The zone allocator is a specialized memory allocator; it performs a similar
function to kmalloc, but it can run from statically allocated structures in
addition to dynamically allocated vm_pages. The zone allocator should be
restricted to use before the VM is initialized and to core VM structures.
.Pp
The zone allocator may block.
.Pp
For more information see
.Xr zone 9 .
.Sh HISTORY
The kmalloc and Zone allocators were inherited from
.Fx .
The kmalloc allocator was converted to a per-CPU slab allocator in
.Dx 1.0 .
.Pp
The MPIPE allocator appeared in
.Dx 1.0 .
The Object cache appeared in
.Dx 1.3 .
.Sh AUTHORS
.An -nosplit
This manual page is based on the
.Nx
analogue, by
.An Elad Efrat Aq Mt elad@NetBSD.org
and
.An YAMAMOTO Takashi Aq Mt yamt@NetBSD.org .