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, 6 insertions, 8 deletions

diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index 8fd6dfbe1bc3..3d7d9631e125 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -79,7 +79,7 @@ void nfs_readdata_release(void *data)
 static
 int nfs_return_empty_page(struct page *page)
 {
-        zero_user_page(page, 0, PAGE_CACHE_SIZE, KM_USER0);
+        zero_user(page, 0, PAGE_CACHE_SIZE);
         SetPageUptodate(page);
         unlock_page(page);
         return 0;
@@ -103,10 +103,10 @@ static void nfs_readpage_truncate_uninitialised_page(struct nfs_read_data *data)
         pglen = PAGE_CACHE_SIZE - base;
         for (;;) {
                 if (remainder <= pglen) {
-                        zero_user_page(*pages, base, remainder, KM_USER0);
+                        zero_user(*pages, base, remainder);
                         break;
                 }
-                zero_user_page(*pages, base, pglen, KM_USER0);
+                zero_user(*pages, base, pglen);
                 pages++;
                 remainder -= pglen;
                 pglen = PAGE_CACHE_SIZE;
@@ -130,7 +130,7 @@ static int nfs_readpage_async(struct nfs_open_context *ctx, struct inode *inode,
                 return PTR_ERR(new);
         }
         if (len < PAGE_CACHE_SIZE)
-                zero_user_page(page, len, PAGE_CACHE_SIZE - len, KM_USER0);
+                zero_user_segment(page, len, PAGE_CACHE_SIZE);
 
         nfs_list_add_request(new, &one_request);
         if (NFS_SERVER(inode)->rsize < PAGE_CACHE_SIZE)
@@ -532,7 +532,7 @@ readpage_async_filler(void *data, struct page *page)
                 goto out_error;
 
         if (len < PAGE_CACHE_SIZE)
-                zero_user_page(page, len, PAGE_CACHE_SIZE - len, KM_USER0);
+                zero_user_segment(page, len, PAGE_CACHE_SIZE);
         nfs_pageio_add_request(desc->pgio, new);
         return 0;
 out_error:
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 522efff3e2c5..b144b1957dd9 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -665,9 +665,7 @@ zero_page:
          * then we need to zero any uninitalised data. */
         if (req->wb_pgbase == 0 && req->wb_bytes != PAGE_CACHE_SIZE
                         && !PageUptodate(req->wb_page))
-                zero_user_page(req->wb_page, req->wb_bytes,
-                                PAGE_CACHE_SIZE - req->wb_bytes,
-                                KM_USER0);
+                zero_user_segment(req->wb_page, req->wb_bytes, PAGE_CACHE_SIZE);
         return req;
 }