Pagecache zeroing: zero_user_segment, zero_user_segments and zero_user

Simplify page cache zeroing of segments of pages through 3 functions

zero_user_segments(page, start1, end1, start2, end2)

        Zeros two segments of the page. It takes the position where to
        start and end the zeroing which avoids length calculations and
	makes code clearer.

zero_user_segment(page, start, end)

        Same for a single segment.

zero_user(page, start, length)

        Length variant for the case where we know the length.

We remove the zero_user_page macro. Issues:

1. Its a macro. Inline functions are preferable.

2. The KM_USER0 macro is only defined for HIGHMEM.

   Having to treat this special case everywhere makes the
   code needlessly complex. The parameter for zeroing is always
   KM_USER0 except in one single case that we open code.

Avoiding KM_USER0 makes a lot of code not having to be dealing
with the special casing for HIGHMEM anymore. Dealing with
kmap is only necessary for HIGHMEM configurations. In those
configurations we use KM_USER0 like we do for a series of other
functions defined in highmem.h.

Since KM_USER0 is depends on HIGHMEM the existing zero_user_page
function could not be a macro. zero_user_* functions introduced
here can be be inline because that constant is not used when these
functions are called.

Also extract the flushing of the caches to be outside of the kmap.

[akpm@linux-foundation.org: fix nfs and ntfs build]
[akpm@linux-foundation.org: fix ntfs build some more]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Steven French <sfrench@us.ibm.com>
Cc: Michael Halcrow <mhalcrow@us.ibm.com>
Cc: <linux-ext4@vger.kernel.org>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Anton Altaparmakov <aia21@cantab.net>
Cc: Mark Fasheh <mark.fasheh@oracle.com>
Cc: David Chinner <dgc@sgi.com>
Cc: Michael Halcrow <mhalcrow@us.ibm.com>
Cc: Steven French <sfrench@us.ibm.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 30 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 456c9ab..1de9214 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1798,7 +1798,7 @@ void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
 					start = max(from, block_start);
 					size = min(to, block_end) - start;
 
-					zero_user_page(page, start, size, KM_USER0);
+					zero_user(page, start, size);
 					set_buffer_uptodate(bh);
 				}
 
@@ -1861,19 +1861,10 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
 					mark_buffer_dirty(bh);
 					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);
-					if (block_start < from)
-						memset(kaddr+block_start,
-							0, from-block_start);
-					flush_dcache_page(page);
-					kunmap_atomic(kaddr, KM_USER0);
-				}
+				if (block_end > to || block_start < from)
+					zero_user_segments(page,
+						to, block_end,
+						block_start, from);
 				continue;
 			}
 		}
@@ -2104,8 +2095,7 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
 					SetPageError(page);
 			}
 			if (!buffer_mapped(bh)) {
-				zero_user_page(page, i * blocksize, blocksize,
-						KM_USER0);
+				zero_user(page, i * blocksize, blocksize);
 				if (!err)
 					set_buffer_uptodate(bh);
 				continue;
@@ -2218,7 +2208,7 @@ int cont_expand_zero(struct file *file, struct address_space *mapping,
 						&page, &fsdata);
 		if (err)
 			goto out;
-		zero_user_page(page, zerofrom, len, KM_USER0);
+		zero_user(page, zerofrom, len);
 		err = pagecache_write_end(file, mapping, curpos, len, len,
 						page, fsdata);
 		if (err < 0)
@@ -2245,7 +2235,7 @@ int cont_expand_zero(struct file *file, struct address_space *mapping,
 						&page, &fsdata);
 		if (err)
 			goto out;
-		zero_user_page(page, zerofrom, len, KM_USER0);
+		zero_user(page, zerofrom, len);
 		err = pagecache_write_end(file, mapping, curpos, len, len,
 						page, fsdata);
 		if (err < 0)
@@ -2422,7 +2412,6 @@ int nobh_write_begin(struct file *file, struct address_space *mapping,
 	unsigned block_in_page;
 	unsigned block_start, block_end;
 	sector_t block_in_file;
-	char *kaddr;
 	int nr_reads = 0;
 	int ret = 0;
 	int is_mapped_to_disk = 1;
@@ -2493,13 +2482,8 @@ int nobh_write_begin(struct file *file, struct address_space *mapping,
 			continue;
 		}
 		if (buffer_new(bh) || !buffer_mapped(bh)) {
-			kaddr = kmap_atomic(page, KM_USER0);
-			if (block_start < from)
-				memset(kaddr+block_start, 0, from-block_start);
-			if (block_end > to)
-				memset(kaddr + to, 0, block_end - to);
-			flush_dcache_page(page);
-			kunmap_atomic(kaddr, KM_USER0);
+			zero_user_segments(page, block_start, from,
+							to, block_end);
 			continue;
 		}
 		if (buffer_uptodate(bh))
@@ -2636,7 +2620,7 @@ int nobh_writepage(struct page *page, get_block_t *get_block,
 	 * the  page size, the remaining memory is zeroed when mapped, and
 	 * writes to that region are not written out to the file."
 	 */
-	zero_user_page(page, offset, PAGE_CACHE_SIZE - offset, KM_USER0);
+	zero_user_segment(page, offset, PAGE_CACHE_SIZE);
 out:
 	ret = mpage_writepage(page, get_block, wbc);
 	if (ret == -EAGAIN)
@@ -2709,7 +2693,7 @@ has_buffers:
 		if (page_has_buffers(page))
 			goto has_buffers;
 	}
-	zero_user_page(page, offset, length, KM_USER0);
+	zero_user(page, offset, length);
 	set_page_dirty(page);
 	err = 0;
 
@@ -2785,7 +2769,7 @@ int block_truncate_page(struct address_space *mapping,
 			goto unlock;
 	}
 
-	zero_user_page(page, offset, length, KM_USER0);
+	zero_user(page, offset, length);
 	mark_buffer_dirty(bh);
 	err = 0;
 
@@ -2831,7 +2815,7 @@ int block_write_full_page(struct page *page, get_block_t *get_block,
 	 * the  page size, the remaining memory is zeroed when mapped, and
 	 * writes to that region are not written out to the file."
 	 */
-	zero_user_page(page, offset, PAGE_CACHE_SIZE - offset, KM_USER0);
+	zero_user_segment(page, offset, PAGE_CACHE_SIZE);
 	return __block_write_full_page(inode, page, get_block, wbc);
 }