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2005-07-12 Yoshinori K. Okuji <okuji@enbug.org> 

* kern/mm.c: Added much documentation.
	(GRUB_MM_ALIGN_LOG2): When GRUB_CPU_SIZEOF_VOID_P is
	8, set to 5 instead of 8.
This commit is contained in:
okuji 2005-07-12 19:33:32 +00:00
parent e0f050c2e4
commit 7ef504d8e0
2 changed files with 49 additions and 2 deletions
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6
ChangeLog
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@ -1,3 +1,9 @@
2005-07-12 Yoshinori K. Okuji <okuji@enbug.org>
* kern/mm.c: Added much documentation.
(GRUB_MM_ALIGN_LOG2): When GRUB_CPU_SIZEOF_VOID_P is
8, set to 5 instead of 8.
2005-07-10 Yoshinori Okuji <okuji@enbug.org>
* DISTLIST: Added util/i386/pc/grub-mkimage.c.

45
kern/mm.c
View File

@ -1,7 +1,7 @@
/* mm.c - functions for memory manager */
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2002 Free Software Foundation, Inc.
* Copyright (C) 2002,2005 Free Software Foundation, Inc.
*
* GRUB is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@ -18,6 +18,47 @@
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
The design of this memory manager.
This is a simple implementation of malloc with a few extensions. These are
the extensions:
- memalign is implemented efficiently.
- multiple regions may be used as free space. They may not be
contiguous.
Regions are managed by a singly linked list, and the meta information is
stored in the beginning of each region. Space after the meta information
is used to allocate memory.
The memory space is used as cells instead of bytes for simplicity. This
is important for some CPUs which may not access multiple bytes at a time
when the first byte is not aligned at a certain boundary (typically,
4-byte or 8-byte). The size of each cell is equal to the size of struct
grub_mm_header, so the header of each allocated/free block fits into one
cell precisely. One cell is 16 bytes on 32-bit platforms and 32 bytes
on 64-bit platforms.
There are two types of blocks: allocated blocks and free blocks.
In allocated blocks, the header of each block has only its size. Note that
this size is based on cells but not on bytes. The header is located right
before the returned pointer, that is, the header resides at the previous
cell.
Free blocks constitutes a ring, using a singly linked list. The first free
block is pointed to by the meta information of a region. The allocator
attempts to pick up the second block instead of the first one. This is
a typical optimization against defragmentation, and makes the
implementation a bit easier.
For safety, both allocated blocks and free ones are marked by magic
numbers. Whenever anything unexpected is detected, GRUB aborts the
operation.
*/
#include <config.h>
#include <grub/mm.h>
#include <grub/misc.h>
@ -48,7 +89,7 @@ typedef struct grub_mm_header
#if GRUB_CPU_SIZEOF_VOID_P == 4
# define GRUB_MM_ALIGN_LOG2 4
#elif GRUB_CPU_SIZEOF_VOID_P == 8
# define GRUB_MM_ALIGN_LOG2 8
# define GRUB_MM_ALIGN_LOG2 5
#endif
#define GRUB_MM_ALIGN (1 << GRUB_MM_ALIGN_LOG2)