Re: [PATCH] x86: reuse the boot-time mappings of fixed_addresses

From: H. Peter Anvin
Date: Sat Aug 29 2009 - 14:18:18 EST

Ingo Molnar wrote:
* Xiao Guangrong <> wrote:

From: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>

Some fixed_addresses items are only used when system boot, after boot, they are free but no way to use, like early ioremap area. They are wasted for us, we can reuse them after system boot.

In this patch, we put them in permanent kmap's area and expand vmalloc's address range. In boot time, reserve them in permanent_kmaps_init() to avoid multiple used, after system boot, we unreserved them then user can use it.

Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>
arch/x86/include/asm/fixmap.h | 2 ++
arch/x86/include/asm/pgtable_32_types.h | 4 ++--
arch/x86/mm/init_32.c | 8 ++++++++
include/linux/highmem.h | 2 ++
mm/highmem.c | 26 ++++++++++++++++++++++++++
5 files changed, 40 insertions(+), 2 deletions(-)

I'm wondering, how much space do we save this way, on a typical bootup on a typical PC?

Not a huge lot... a few dozen pages.

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