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add some description about the vmem arenas, how they stack up and their purpose

This commit is contained in:
para 2012-06-02 08:42:37 +00:00
parent 5a5317f49b
commit c8f20a5780
1 changed files with 27 additions and 3 deletions
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30
sys/uvm/uvm_km.c
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@ -1,4 +1,4 @@
/* $NetBSD: uvm_km.c,v 1.125 2012/04/13 15:34:42 yamt Exp $ */
/* $NetBSD: uvm_km.c,v 1.126 2012/06/02 08:42:37 para Exp $ */
/*
* Copyright (c) 1997 Charles D. Cranor and Washington University.
@ -83,11 +83,15 @@
* up the locking and protection of the kernel address space into smaller
* chunks.
*
* the vm system has several standard kernel submaps, including:
* the vm system has several standard kernel submaps/arenas, including:
* kmem_arena => used for kmem/pool (memoryallocators(9))
* pager_map => used to map "buf" structures into kernel space
* exec_map => used during exec to handle exec args
* etc...
*
* the kmem_arena is a "special submap", as it lives a fixed map entry
* within the kernel_map and controlled by vmem(9).
*
* the kernel allocates its private memory out of special uvm_objects whose
* reference count is set to UVM_OBJ_KERN (thus indicating that the objects
* are "special" and never die). all kernel objects should be thought of
@ -117,10 +121,30 @@
* freed right away. this is done with the uvm_km_pgremove() function.
* this has to be done because there is no backing store for kernel pages
* and no need to save them after they are no longer referenced.
*
* kmem_arena: main arena controlling the kernel kva used by other arenas.
* kmem_va_arena: it utilizes quantum caching for fast allocations and to
* lower fragmentation. the pool and kmem allocate from this arena
* except for some pool meta-data.
*
* arenas for metadata allocations used by vmem(9) and pool(9)
* note: these arenas can't use quantum caching, the kmem_va_meta_arena
* compensates for this by importing larger chunks from kmem_arena.
*
* kmem_va_meta_arena: space for metadata is allocated from this arena.
* kmem_meta_arena: imports from kmem_va_meta_arena.
* allocations from this arena are backed with vm_pages.
*
* arena stacking:
* kmem_arena
* kmem_va_arena
* kmem_va_meta_arena
* kmem_meta_arena
*
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: uvm_km.c,v 1.125 2012/04/13 15:34:42 yamt Exp $");
__KERNEL_RCSID(0, "$NetBSD: uvm_km.c,v 1.126 2012/06/02 08:42:37 para Exp $");
#include "opt_uvmhist.h"