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MEMORY(9)             DragonFly Kernel Developer's Manual            MEMORY(9)


NAME

     memory -- introduction to kernel memory allocators


DESCRIPTION

     The DragonFly kernel provides several memory allocators, each with dif-
     ferent characteristics and purposes.

   kmalloc
     kmalloc is the primary kernel memory allocator. kmalloc allocates pages
     from the kernel address space via 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 alloca-
     tion statistics in a malloc_zone structure, which must be declared before
     use.

     kmalloc is implemented as a slab allocator, with per-CPU slab structures.
     It may block while attempting to get free pages.

     For more information, see kmalloc(9).

   Object caches
     The object cache is a frontend memory allocator to some backing alloca-
     tor. 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.

     The object cache routines may block allocating cache structures or buf-
     fers.

     For more information, see objcache(9).

   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.

     For more information see mpipe(9).

   The Zone Allocator
     The zone allocator is a specialized memory allocator; it performs a simi-
     lar function to kmalloc, but it can run from statically allocated struc-
     tures 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.

     The zone allocator may block.

     For more information see zone(9).


HISTORY

     The kmalloc and Zone allocators were inherited from FreeBSD.  The kmalloc
     allocator was converted to a per-CPU slab allocator in DragonFly 1.0.

     The MPIPE allocator appeared in DragonFly 1.0.  The Object cache appeared
     in DragonFly 1.3.


AUTHORS

     This manual page is based on the NetBSD analogue, by Elad Efrat
     <elad@NetBSD.org> and YAMAMOTO Takashi <yamt@NetBSD.org>.

DragonFly 3.5                   March 23, 2011                   DragonFly 3.5

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