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>

2 files changed, 4 insertions, 4 deletions

diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
index 64713e1..447206eb 100644
--- a/fs/ocfs2/alloc.c
+++ b/fs/ocfs2/alloc.c
@@ -5670,7 +5670,7 @@ static void ocfs2_map_and_dirty_page(struct inode *inode, handle_t *handle,
 		mlog_errno(ret);
 
 	if (zero)
-		zero_user_page(page, from, to - from, KM_USER0);
+		zero_user_segment(page, from, to);
 
 	/*
 	 * Need to set the buffers we zero'd into uptodate
diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index bc7b4cb..8224312 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -307,7 +307,7 @@ static int ocfs2_readpage(struct file *file, struct page *page)
 	 * XXX sys_readahead() seems to get that wrong?
 	 */
 	if (start >= i_size_read(inode)) {
-		zero_user_page(page, 0, PAGE_SIZE, KM_USER0);
+		zero_user(page, 0, PAGE_SIZE);
 		SetPageUptodate(page);
 		ret = 0;
 		goto out_alloc;
@@ -869,7 +869,7 @@ int ocfs2_map_page_blocks(struct page *page, u64 *p_blkno,
 		if (block_start >= to)
 			break;
 
-		zero_user_page(page, block_start, bh->b_size, KM_USER0);
+		zero_user(page, block_start, bh->b_size);
 		set_buffer_uptodate(bh);
 		mark_buffer_dirty(bh);
 
@@ -1034,7 +1034,7 @@ static void ocfs2_zero_new_buffers(struct page *page, unsigned from, unsigned to
 					start = max(from, block_start);
 					end = min(to, block_end);
 
-					zero_user_page(page, start, end - start, KM_USER0);
+					zero_user_segment(page, start, end);
 					set_buffer_uptodate(bh);
 				}