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Commit 41cb8ac0 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

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: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 902aaed0

mm/filemap.c

+13 −19
Original line number Diff line number Diff line
@@ -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

		 */

		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.

		 * 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);



		/*

			 * 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.

		 * 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;