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authorYuri Tikhonov <yur@emcraft.com>2009-01-29 01:40:44 +0000
committerJosh Boyer <jwboyer@linux.vnet.ibm.com>2009-02-14 14:40:04 -0500
commite12401222f749c37277a313d631dc024bbfd3b00 (patch)
tree5e02daa9f2c16965a2399a5b7189ddd0753f0fb1 /arch/powerpc/include/asm/highmem.h
parent6071ed0487c6ea8dcfadd9844b9b90944cd9de1e (diff)
powerpc/44x: Support for 256KB PAGE_SIZE
This patch adds support for 256KB pages on ppc44x-based boards. For simplification of implementation with 256KB pages we still assume 2-level paging. As a side effect this leads to wasting extra memory space reserved for PTE tables: only 1/4 of pages allocated for PTEs are actually used. But this may be an acceptable trade-off to achieve the high performance we have with big PAGE_SIZEs in some applications (e.g. RAID). Also with 256KB PAGE_SIZE we increase THREAD_SIZE up to 32KB to minimize the risk of stack overflows in the cases of on-stack arrays, which size depends on the page size (e.g. multipage BIOs, NTFS, etc.). With 256KB PAGE_SIZE we need to decrease the PKMAP_ORDER at least down to 9, otherwise all high memory (2 ^ 10 * PAGE_SIZE == 256MB) we'll be occupied by PKMAP addresses leaving no place for vmalloc. We do not separate PKMAP_ORDER for 256K from 16K/64K PAGE_SIZE here; actually that value of 10 in support for 16K/64K had been selected rather intuitively. Thus now for all cases of PAGE_SIZE on ppc44x (including the default, 4KB, one) we have 512 pages for PKMAP. Because ELF standard supports only page sizes up to 64K, then you should use binutils later than 2.17.50.0.3 with '-zmax-page-size' set to 256K for building applications, which are to be run with the 256KB-page sized kernel. If using the older binutils, then you should patch them like follows: --- binutils/bfd/elf32-ppc.c.orig +++ binutils/bfd/elf32-ppc.c -#define ELF_MAXPAGESIZE 0x10000 +#define ELF_MAXPAGESIZE 0x40000 One more restriction we currently have with 256KB page sizes is inability to use shmem safely, so, for now, the 256KB is available only if you turn the CONFIG_SHMEM option off (another variant is to use BROKEN). Though, if you need shmem with 256KB pages, you can always remove the !SHMEM dependency in 'config PPC_256K_PAGES', and use the workaround available here: http://lkml.org/lkml/2008/12/19/20 Signed-off-by: Yuri Tikhonov <yur@emcraft.com> Signed-off-by: Ilya Yanok <yanok@emcraft.com> Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Diffstat (limited to 'arch/powerpc/include/asm/highmem.h')
-rw-r--r--arch/powerpc/include/asm/highmem.h10
1 files changed, 5 insertions, 5 deletions
diff --git a/arch/powerpc/include/asm/highmem.h b/arch/powerpc/include/asm/highmem.h
index 04e4a620952..a2907595067 100644
--- a/arch/powerpc/include/asm/highmem.h
+++ b/arch/powerpc/include/asm/highmem.h
@@ -39,15 +39,15 @@ extern pte_t *pkmap_page_table;
* chunk of RAM.
*/
/*
- * We use one full pte table with 4K pages. And with 16K/64K pages pte
- * table covers enough memory (32MB and 512MB resp.) that both FIXMAP
- * and PKMAP can be placed in single pte table. We use 1024 pages for
- * PKMAP in case of 16K/64K pages.
+ * We use one full pte table with 4K pages. And with 16K/64K/256K pages pte
+ * table covers enough memory (32MB/512MB/2GB resp.), so that both FIXMAP
+ * and PKMAP can be placed in a single pte table. We use 512 pages for PKMAP
+ * in case of 16K/64K/256K page sizes.
*/
#ifdef CONFIG_PPC_4K_PAGES
#define PKMAP_ORDER PTE_SHIFT
#else
-#define PKMAP_ORDER 10
+#define PKMAP_ORDER 9
#endif
#define LAST_PKMAP (1 << PKMAP_ORDER)
#ifndef CONFIG_PPC_4K_PAGES