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Subject[PATCH] add a clear_pages function to clear pages of higher order
The zeroing of a page of a arbitrary order in page_alloc.c and in hugetlb.c may benefit from a
clear_page that is capable of zeroing multiple pages at once. The following patch adds
a function "clear_pages" that is capable of clearing multiple continuous pages at once.

This used to be part of the prezeroing patchset but there may be benefits
to huge pages and regular kernel code as well. Also Mel Gorman's patchset
to reduce fragmentation and introduce prezeroing in a different way may
benefit from this patch. The patch only provides a clear_pages function
for ia32, ia64, x86_64 and sparc64 (all tested). Other platforms may
provide a clear_pages function by defining __HAVE_ARCH_CLEAR_PAGES.

Patch against 2.6.11-bk6

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.11/mm/page_alloc.c
===================================================================
--- linux-2.6.11.orig/mm/page_alloc.c 2005-03-10 10:57:06.000000000 -0800
+++ linux-2.6.11/mm/page_alloc.c 2005-03-10 10:57:10.000000000 -0800
@@ -628,11 +628,19 @@ void fastcall free_cold_page(struct page
free_hot_cold_page(page, 1);
}

-static inline void prep_zero_page(struct page *page, int order, int gfp_flags)
+void prep_zero_page(struct page *page, unsigned int order, unsigned int gfp_flags)
{
int i;

BUG_ON((gfp_flags & (__GFP_WAIT | __GFP_HIGHMEM)) == __GFP_HIGHMEM);
+
+#ifdef __HAVE_ARCH_CLEAR_PAGES
+ if (!PageHighMem(page)) {
+ clear_pages(page_address(page), order);
+ return;
+ }
+#endif
+
for(i = 0; i < (1 << order); i++)
clear_highpage(page + i);
}
Index: linux-2.6.11/mm/hugetlb.c
===================================================================
--- linux-2.6.11.orig/mm/hugetlb.c 2005-03-01 23:38:12.000000000 -0800
+++ linux-2.6.11/mm/hugetlb.c 2005-03-10 10:57:10.000000000 -0800
@@ -78,7 +78,6 @@ void free_huge_page(struct page *page)
struct page *alloc_huge_page(void)
{
struct page *page;
- int i;

spin_lock(&hugetlb_lock);
page = dequeue_huge_page();
@@ -89,8 +88,7 @@ struct page *alloc_huge_page(void)
spin_unlock(&hugetlb_lock);
set_page_count(page, 1);
page[1].mapping = (void *)free_huge_page;
- for (i = 0; i < (HPAGE_SIZE/PAGE_SIZE); ++i)
- clear_highpage(&page[i]);
+ prep_zero_page(page, HUGETLB_PAGE_ORDER, GFP_HIGHUSER);
return page;
}

Index: linux-2.6.11/include/asm-ia64/page.h
===================================================================
--- linux-2.6.11.orig/include/asm-ia64/page.h 2005-03-01 23:37:48.000000000 -0800
+++ linux-2.6.11/include/asm-ia64/page.h 2005-03-10 10:57:10.000000000 -0800
@@ -56,8 +56,10 @@
# ifdef __KERNEL__
# define STRICT_MM_TYPECHECKS

-extern void clear_page (void *page);
+extern void clear_pages (void *page, int order);
extern void copy_page (void *to, void *from);
+#define clear_page(__page) clear_pages(__page, 0)
+#define __HAVE_ARCH_CLEAR_PAGES

/*
* clear_user_page() and copy_user_page() can't be inline functions because
Index: linux-2.6.11/arch/ia64/kernel/ia64_ksyms.c
===================================================================
--- linux-2.6.11.orig/arch/ia64/kernel/ia64_ksyms.c 2005-03-01 23:38:08.000000000 -0800
+++ linux-2.6.11/arch/ia64/kernel/ia64_ksyms.c 2005-03-10 10:57:10.000000000 -0800
@@ -38,7 +38,7 @@ EXPORT_SYMBOL(__down_trylock);
EXPORT_SYMBOL(__up);

#include <asm/page.h>
-EXPORT_SYMBOL(clear_page);
+EXPORT_SYMBOL(clear_pages);

#ifdef CONFIG_VIRTUAL_MEM_MAP
#include <linux/bootmem.h>
Index: linux-2.6.11/arch/ia64/lib/clear_page.S
===================================================================
--- linux-2.6.11.orig/arch/ia64/lib/clear_page.S 2005-03-01 23:37:47.000000000 -0800
+++ linux-2.6.11/arch/ia64/lib/clear_page.S 2005-03-10 10:57:10.000000000 -0800
@@ -7,6 +7,7 @@
* 1/06/01 davidm Tuned for Itanium.
* 2/12/02 kchen Tuned for both Itanium and McKinley
* 3/08/02 davidm Some more tweaking
+ * 12/10/04 clameter Make it work on pages of order size
*/
#include <linux/config.h>

@@ -29,27 +30,33 @@
#define dst4 r11

#define dst_last r31
+#define totsize r14

-GLOBAL_ENTRY(clear_page)
+GLOBAL_ENTRY(clear_pages)
.prologue
- .regstk 1,0,0,0
- mov r16 = PAGE_SIZE/L3_LINE_SIZE-1 // main loop count, -1=repeat/until
+ .regstk 2,0,0,0
+ mov r16 = PAGE_SIZE/L3_LINE_SIZE // main loop count
+ mov totsize = PAGE_SIZE
.save ar.lc, saved_lc
mov saved_lc = ar.lc
-
+ ;;
.body
+ adds dst1 = 16, in0
mov ar.lc = (PREFETCH_LINES - 1)
mov dst_fetch = in0
- adds dst1 = 16, in0
adds dst2 = 32, in0
+ shl r16 = r16, in1
+ shl totsize = totsize, in1
;;
.fetch: stf.spill.nta [dst_fetch] = f0, L3_LINE_SIZE
adds dst3 = 48, in0 // executing this multiple times is harmless
br.cloop.sptk.few .fetch
+ add r16 = -1,r16
+ add dst_last = totsize, dst_fetch
+ adds dst4 = 64, in0
;;
- addl dst_last = (PAGE_SIZE - PREFETCH_LINES*L3_LINE_SIZE), dst_fetch
mov ar.lc = r16 // one L3 line per iteration
- adds dst4 = 64, in0
+ adds dst_last = -PREFETCH_LINES*L3_LINE_SIZE, dst_last
;;
#ifdef CONFIG_ITANIUM
// Optimized for Itanium
@@ -74,4 +81,4 @@ GLOBAL_ENTRY(clear_page)
;;
mov ar.lc = saved_lc // restore lc
br.ret.sptk.many rp
-END(clear_page)
+END(clear_pages)
Index: linux-2.6.11/include/asm-i386/page.h
===================================================================
--- linux-2.6.11.orig/include/asm-i386/page.h 2005-03-01 23:37:49.000000000 -0800
+++ linux-2.6.11/include/asm-i386/page.h 2005-03-10 10:57:10.000000000 -0800
@@ -18,7 +18,7 @@

#include <asm/mmx.h>

-#define clear_page(page) mmx_clear_page((void *)(page))
+#define clear_pages(page, order) mmx_clear_page((void *)(page),order)
#define copy_page(to,from) mmx_copy_page(to,from)

#else
@@ -28,11 +28,13 @@
* Maybe the K6-III ?
*/

-#define clear_page(page) memset((void *)(page), 0, PAGE_SIZE)
+#define clear_pages(page, order) memset((void *)(page), 0, PAGE_SIZE << (order))
#define copy_page(to,from) memcpy((void *)(to), (void *)(from), PAGE_SIZE)

#endif

+#define __HAVE_ARCH_CLEAR_PAGES
+#define clear_page(page) clear_pages(page, 0)
#define clear_user_page(page, vaddr, pg) clear_page(page)
#define copy_user_page(to, from, vaddr, pg) copy_page(to, from)

Index: linux-2.6.11/include/asm-i386/mmx.h
===================================================================
--- linux-2.6.11.orig/include/asm-i386/mmx.h 2005-03-01 23:38:09.000000000 -0800
+++ linux-2.6.11/include/asm-i386/mmx.h 2005-03-10 10:57:10.000000000 -0800
@@ -8,7 +8,7 @@
#include <linux/types.h>

extern void *_mmx_memcpy(void *to, const void *from, size_t size);
-extern void mmx_clear_page(void *page);
+extern void mmx_clear_page(void *page, int order);
extern void mmx_copy_page(void *to, void *from);

#endif
Index: linux-2.6.11/arch/i386/lib/mmx.c
===================================================================
--- linux-2.6.11.orig/arch/i386/lib/mmx.c 2005-03-01 23:38:09.000000000 -0800
+++ linux-2.6.11/arch/i386/lib/mmx.c 2005-03-10 10:57:10.000000000 -0800
@@ -128,7 +128,7 @@ void *_mmx_memcpy(void *to, const void *
* other MMX using processors do not.
*/

-static void fast_clear_page(void *page)
+static void fast_clear_page(void *page, int order)
{
int i;

@@ -138,7 +138,7 @@ static void fast_clear_page(void *page)
" pxor %%mm0, %%mm0\n" : :
);

- for(i=0;i<4096/64;i++)
+ for(i=0;i<((4096/64) << order);i++)
{
__asm__ __volatile__ (
" movntq %%mm0, (%0)\n"
@@ -257,7 +257,7 @@ static void fast_copy_page(void *to, voi
* Generic MMX implementation without K7 specific streaming
*/

-static void fast_clear_page(void *page)
+static void fast_clear_page(void *page, int order)
{
int i;

@@ -267,7 +267,7 @@ static void fast_clear_page(void *page)
" pxor %%mm0, %%mm0\n" : :
);

- for(i=0;i<4096/128;i++)
+ for(i=0;i<((4096/128) << order);i++)
{
__asm__ __volatile__ (
" movq %%mm0, (%0)\n"
@@ -359,23 +359,23 @@ static void fast_copy_page(void *to, voi
* Favour MMX for page clear and copy.
*/

-static void slow_zero_page(void * page)
+static void slow_clear_page(void * page, int order)
{
int d0, d1;
__asm__ __volatile__( \
"cld\n\t" \
"rep ; stosl" \
: "=&c" (d0), "=&D" (d1)
- :"a" (0),"1" (page),"0" (1024)
+ :"a" (0),"1" (page),"0" (1024 << order)
:"memory");
}
-
-void mmx_clear_page(void * page)
+
+void mmx_clear_page(void * page, int order)
{
if(unlikely(in_interrupt()))
- slow_zero_page(page);
+ slow_clear_page(page, order);
else
- fast_clear_page(page);
+ fast_clear_page(page, order);
}

static void slow_copy_page(void *to, void *from)
Index: linux-2.6.11/include/asm-x86_64/page.h
===================================================================
--- linux-2.6.11.orig/include/asm-x86_64/page.h 2005-03-01 23:37:47.000000000 -0800
+++ linux-2.6.11/include/asm-x86_64/page.h 2005-03-10 10:57:10.000000000 -0800
@@ -32,8 +32,10 @@
#ifdef __KERNEL__
#ifndef __ASSEMBLY__

-void clear_page(void *);
+void clear_pages(void *, int);
void copy_page(void *, void *);
+#define __HAVE_ARCH_CLEAR_PAGES
+#define clear_page(__page) clear_pages(__page, 0)

#define clear_user_page(page, vaddr, pg) clear_page(page)
#define copy_user_page(to, from, vaddr, pg) copy_page(to, from)
Index: linux-2.6.11/arch/x86_64/kernel/x8664_ksyms.c
===================================================================
--- linux-2.6.11.orig/arch/x86_64/kernel/x8664_ksyms.c 2005-03-01 23:37:49.000000000 -0800
+++ linux-2.6.11/arch/x86_64/kernel/x8664_ksyms.c 2005-03-10 10:57:10.000000000 -0800
@@ -108,7 +108,7 @@ EXPORT_SYMBOL(pci_mem_start);
#endif

EXPORT_SYMBOL(copy_page);
-EXPORT_SYMBOL(clear_page);
+EXPORT_SYMBOL(clear_pages);

EXPORT_SYMBOL(cpu_pda);
#ifdef CONFIG_SMP
Index: linux-2.6.11/arch/x86_64/lib/clear_page.S
===================================================================
--- linux-2.6.11.orig/arch/x86_64/lib/clear_page.S 2005-03-01 23:38:08.000000000 -0800
+++ linux-2.6.11/arch/x86_64/lib/clear_page.S 2005-03-10 10:57:10.000000000 -0800
@@ -1,12 +1,16 @@
/*
* Zero a page.
* rdi page
+ * rsi order
*/
- .globl clear_page
+ .globl clear_pages
.p2align 4
-clear_page:
+clear_pages:
+ movl $4096/64,%eax
+ movl %esi, %ecx
+ shll %cl, %eax
+ movl %eax, %ecx
xorl %eax,%eax
- movl $4096/64,%ecx
.p2align 4
.Lloop:
decl %ecx
@@ -23,7 +27,7 @@ clear_page:
jnz .Lloop
nop
ret
-clear_page_end:
+clear_pages_end:

/* C stepping K8 run faster using the string instructions.
It is also a lot simpler. Use this when possible */
@@ -32,19 +36,22 @@ clear_page_end:

.section .altinstructions,"a"
.align 8
- .quad clear_page
- .quad clear_page_c
+ .quad clear_pages
+ .quad clear_pages_c
.byte X86_FEATURE_K8_C
- .byte clear_page_end-clear_page
- .byte clear_page_c_end-clear_page_c
+ .byte clear_pages_end-clear_pages
+ .byte clear_pages_c_end-clear_pages_c
.previous

.section .altinstr_replacement,"ax"
-clear_page_c:
- movl $4096/8,%ecx
+clear_pages_c:
+ movl $4096/8,%eax
+ movl %esi, %ecx
+ shll %cl, %eax
+ movl %eax, %ecx
xorl %eax,%eax
rep
stosq
ret
-clear_page_c_end:
+clear_pages_c_end:
.previous
Index: linux-2.6.11/arch/sparc64/lib/clear_page.S
===================================================================
--- linux-2.6.11.orig/arch/sparc64/lib/clear_page.S 2005-03-01 23:38:17.000000000 -0800
+++ linux-2.6.11/arch/sparc64/lib/clear_page.S 2005-03-10 10:57:10.000000000 -0800
@@ -28,9 +28,12 @@
.text

.globl _clear_page
-_clear_page: /* %o0=dest */
+_clear_page: /* %o0=dest, %o1=order */
+ sethi %hi(PAGE_SIZE/64), %o2
+ clr %o4
+ or %o2, %lo(PAGE_SIZE/64), %o2
ba,pt %xcc, clear_page_common
- clr %o4
+ sllx %o2, %o1, %o1

/* This thing is pretty important, it shows up
* on the profiles via do_anonymous_page().
@@ -69,16 +72,16 @@ clear_user_page: /* %o0=dest, %o1=vaddr
flush %g6
wrpr %o4, 0x0, %pstate

+ sethi %hi(PAGE_SIZE/64), %o1
mov 1, %o4
+ or %o1, %lo(PAGE_SIZE/64), %o1

clear_page_common:
VISEntryHalf
membar #StoreLoad | #StoreStore | #LoadStore
fzero %f0
- sethi %hi(PAGE_SIZE/64), %o1
mov %o0, %g1 ! remember vaddr for tlbflush
fzero %f2
- or %o1, %lo(PAGE_SIZE/64), %o1
faddd %f0, %f2, %f4
fmuld %f0, %f2, %f6
faddd %f0, %f2, %f8
Index: linux-2.6.11/include/asm-sparc64/page.h
===================================================================
--- linux-2.6.11.orig/include/asm-sparc64/page.h 2005-03-01 23:38:07.000000000 -0800
+++ linux-2.6.11/include/asm-sparc64/page.h 2005-03-10 10:57:10.000000000 -0800
@@ -14,8 +14,10 @@

#ifndef __ASSEMBLY__

-extern void _clear_page(void *page);
-#define clear_page(X) _clear_page((void *)(X))
+extern void _clear_page(void *page, int order);
+#define clear_page(X) _clear_page((void *)(X), 0)
+#define clear_pages _clear_page
+
struct page;
extern void clear_user_page(void *addr, unsigned long vaddr, struct page *page);
#define copy_page(X,Y) memcpy((void *)(X), (void *)(Y), PAGE_SIZE)
Index: linux-2.6.11/include/linux/gfp.h
===================================================================
--- linux-2.6.11.orig/include/linux/gfp.h 2005-03-01 23:37:50.000000000 -0800
+++ linux-2.6.11/include/linux/gfp.h 2005-03-10 10:57:10.000000000 -0800
@@ -131,4 +131,5 @@ extern void FASTCALL(free_cold_page(stru

void page_alloc_init(void);

+void prep_zero_page(struct page *, unsigned int order, unsigned int gfp_flags);
#endif /* __LINUX_GFP_H */
-
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