Remove open coded implementation of memclear_highpage flush

There are a series of open coded reimplementation of memclear_highpage_flush
all over the page cache code. Call memclear_highpage_flush in those locations.
Consolidates code and eases maintenance.

[There seems to be a better patch in mm. This patch here is just to make things
work against 2.6.21 until the rest of the patch is diffed against mm]

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

---
 fs/buffer.c |   23 ++++++++---------------
 fs/libfs.c  |   10 +++++-----
 2 files changed, 13 insertions(+), 20 deletions(-)

Index: linux-2.6.21-rc7-mm1/fs/buffer.c
===================================================================
--- linux-2.6.21-rc7-mm1.orig/fs/buffer.c	2007-04-25 00:17:31.000000000 -0700
+++ linux-2.6.21-rc7-mm1/fs/buffer.c	2007-04-25 00:18:17.000000000 -0700
@@ -1797,17 +1797,12 @@ static int __block_prepare_write(struct 
 					continue;
 				}
 				if (block_end > to || block_start < from) {
-					void *kaddr;
-
-					kaddr = kmap_atomic(page, KM_USER0);
 					if (block_end > to)
-						memset(kaddr+to, 0,
-							block_end-to);
+						memclear_highpage_flush(page,
+							to, block_end - to);
 					if (block_start < from)
-						memset(kaddr+block_start,
-							0, from-block_start);
-					flush_dcache_page(page);
-					kunmap_atomic(kaddr, KM_USER0);
+						memclear_highpage_flush(page,
+						block_start, from - block_start);
 				}
 				continue;
 			}
@@ -2224,7 +2219,6 @@ int nobh_prepare_write(struct page *page
 	unsigned block_in_page;
 	unsigned block_start;
 	sector_t block_in_file;
-	char *kaddr;
 	int nr_reads = 0;
 	int i;
 	int ret = 0;
@@ -2264,13 +2258,12 @@ int nobh_prepare_write(struct page *page
 		if (PageUptodate(page))
 			continue;
 		if (buffer_new(&map_bh) || !buffer_mapped(&map_bh)) {
-			kaddr = kmap_atomic(page, KM_USER0);
 			if (block_start < from)
-				memset(kaddr+block_start, 0, from-block_start);
+				memclear_highpage_flush(page,
+					block_start, from - block_start);
 			if (block_end > to)
-				memset(kaddr + to, 0, block_end - to);
-			flush_dcache_page(page);
-			kunmap_atomic(kaddr, KM_USER0);
+				memclear_highpage_flush(page,
+					to, block_end - to);
 			continue;
 		}
 		if (buffer_uptodate(&map_bh))
Index: linux-2.6.21-rc7-mm1/fs/libfs.c
===================================================================
--- linux-2.6.21-rc7-mm1.orig/fs/libfs.c	2007-04-25 00:17:22.000000000 -0700
+++ linux-2.6.21-rc7-mm1/fs/libfs.c	2007-04-25 00:18:17.000000000 -0700
@@ -338,11 +338,11 @@ int simple_prepare_write(struct file *fi
 {
 	if (!PageUptodate(page)) {
 		if (to - from != PAGE_CACHE_SIZE) {
-			void *kaddr = kmap_atomic(page, KM_USER0);
-			memset(kaddr, 0, from);
-			memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
-			flush_dcache_page(page);
-			kunmap_atomic(kaddr, KM_USER0);
+			if (from)
+				memclear_highpage_flush(page, 0, from);
+			if (to < PAGE_CACHE_SIZE)
+				memclear_highpage_flush(page, to,
+					PAGE_CACHE_SIZE - to);
 		}
 	}
 	return 0;