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x86: Lift restriction on the location of FIX_BTMAP_* 

The early ioremap fixmap entries cover half (or for 32-bit
non-PAE, a quarter) of a page table, yet they got
uncondtitionally aligned so far to a 256-entry boundary. This is
not necessary if the range of page table entries anyway falls
into a single page table.

This buys back, for (theoretically) 50% of all configurations
(25% of all non-PAE ones), at least some of the lowmem
necessarily lost with commit e621bd1895.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <4B2BB66F0200007800026AD6@vpn.id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Jan Beulich 2009-12-18 16:05:51 +00:00 committed by Ingo Molnar
parent 39d997b514
commit 499a5f1efa
2 changed files with 15 additions and 5 deletions
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16
arch/x86/include/asm/fixmap.h
View File

@ -118,14 +118,20 @@ enum fixed_addresses {
* 256 temporary boot-time mappings, used by early_ioremap(),
* before ioremap() is functional.
*
* We round it up to the next 256 pages boundary so that we
* can have a single pgd entry and a single pte table:
* If necessary we round it up to the next 256 pages boundary so
* that we can have a single pgd entry and a single pte table:
*/
#define NR_FIX_BTMAPS 64
#define FIX_BTMAPS_SLOTS 4
FIX_BTMAP_END = __end_of_permanent_fixed_addresses + 256 -
(__end_of_permanent_fixed_addresses & 255),
FIX_BTMAP_BEGIN = FIX_BTMAP_END + NR_FIX_BTMAPS*FIX_BTMAPS_SLOTS - 1,
#define TOTAL_FIX_BTMAPS (NR_FIX_BTMAPS * FIX_BTMAPS_SLOTS)
FIX_BTMAP_END =
(__end_of_permanent_fixed_addresses ^
(__end_of_permanent_fixed_addresses + TOTAL_FIX_BTMAPS - 1)) &
-PTRS_PER_PTE
? __end_of_permanent_fixed_addresses + TOTAL_FIX_BTMAPS -
(__end_of_permanent_fixed_addresses & (TOTAL_FIX_BTMAPS - 1))
: __end_of_permanent_fixed_addresses,
FIX_BTMAP_BEGIN = FIX_BTMAP_END + TOTAL_FIX_BTMAPS - 1,
#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
FIX_OHCI1394_BASE,
#endif

4
arch/x86/mm/ioremap.c
View File

@ -422,6 +422,10 @@ void __init early_ioremap_init(void)
* The boot-ioremap range spans multiple pmds, for which
* we are not prepared:
*/
#define __FIXADDR_TOP (-PAGE_SIZE)
BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
!= (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));
#undef __FIXADDR_TOP
if (pmd != early_ioremap_pmd(fix_to_virt(FIX_BTMAP_END))) {
WARN_ON(1);
printk(KERN_WARNING "pmd %p != %p\n",