mm: revert KERNEL_DS buffered write optimisation

Revert the patch from Neil Brown to optimise NFSD writev handling.

Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index 7989c44cb293d09c5c6b306128aceafdb369d311..c504db18ac2640d2344e151d6712b94b5f433a96 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1874,27 +1874,21 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
                /* Limit the size of the copy to the caller's write size */
                bytes = min(bytes, count);
 
-               /* We only need to worry about prefaulting when writes are from
-                * user-space.  NFSd uses vfs_writev with several non-aligned
-                * segments in the vector, and limiting to one segment a time is
-                * a noticeable performance for re-write
+               /*
+                * Limit the size of the copy to that of the current segment,
+                * because fault_in_pages_readable() doesn't know how to walk
+                * segments.
                 */
-               if (!segment_eq(get_fs(), KERNEL_DS)) {
-                       /*
-                        * Limit the size of the copy to that of the current
-                        * segment, because fault_in_pages_readable() doesn't
-                        * know how to walk segments.
-                        */
-                       bytes = min(bytes, cur_iov->iov_len - iov_base);
+               bytes = min(bytes, cur_iov->iov_len - iov_base);
+
+               /*
+                * Bring in the user page that we will copy from _first_.
+                * Otherwise there's a nasty deadlock on copying from the
+                * same page as we're writing to, without it being marked
+                * up-to-date.
+                */
+               fault_in_pages_readable(buf, bytes);
 
-                       /*
-                        * Bring in the user page that we will copy from
-                        * _first_.  Otherwise there's a nasty deadlock on
-                        * copying from the same page as we're writing to,
-                        * without it being marked up-to-date.
-                        */
-                       fault_in_pages_readable(buf, bytes);
-               }
                page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec);
                if (!page) {
                        status = -ENOMEM;