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authorJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>2009-02-27 01:35:44 (GMT)
committerH. Peter Anvin <hpa@zytor.com>2009-03-14 22:37:14 (GMT)
commit93dbda7cbcd70a0bd1a99f39f44a9ccde8ab9040 (patch)
tree132347cd952fb8281247c1fb38ec1c608c19a3f6 /arch/x86/kernel/head32.c
parentb9719a4d9cfa5d46fa6a1eb3e3fc2238e7981e4d (diff)
x86: add brk allocation for very, very early allocations
Impact: new interface Add a brk()-like allocator which effectively extends the bss in order to allow very early code to do dynamic allocations. This is better than using statically allocated arrays for data in subsystems which may never get used. The space for brk allocations is in the bss ELF segment, so that the space is mapped properly by the code which maps the kernel, and so that bootloaders keep the space free rather than putting a ramdisk or something into it. The bss itself, delimited by __bss_stop, ends before the brk area (__brk_base to __brk_limit). The kernel text, data and bss is reserved up to __bss_stop. Any brk-allocated data is reserved separately just before the kernel pagetable is built, as that code allocates from unreserved spaces in the e820 map, potentially allocating from any unused brk memory. Ultimately any unused memory in the brk area is used in the general kernel memory pool. Initially the brk space is set to 1MB, which is probably much larger than any user needs (the largest current user is i386 head_32.S's code to build the pagetables to map the kernel, which can get fairly large with a big kernel image and no PSE support). So long as the system has sufficient memory for the bootloader to reserve the kernel+1MB brk, there are no bad effects resulting from an over-large brk. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/kernel/head32.c')
-rw-r--r--arch/x86/kernel/head32.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
index ac108d1..29f1095 100644
--- a/arch/x86/kernel/head32.c
+++ b/arch/x86/kernel/head32.c
@@ -18,7 +18,7 @@ void __init i386_start_kernel(void)
{
reserve_trampoline_memory();
- reserve_early(__pa_symbol(&_text), __pa_symbol(&_end), "TEXT DATA BSS");
+ reserve_early(__pa_symbol(&_text), __pa_symbol(&__bss_stop), "TEXT DATA BSS");
#ifdef CONFIG_BLK_DEV_INITRD
/* Reserve INITRD */

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