From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH] Teach do_mpage_readpage() about unwritten buffers Date: Mon, 2 Jul 2007 20:28:27 -0700 Message-ID: <20070702202827.ffc59255.akpm@linux-foundation.org> References: <20070703011019.GQ989688@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: lkml , xfs-oss , "linux-ext4@vger.kernel.org" To: David Chinner Return-path: Received: from smtp2.linux-foundation.org ([207.189.120.14]:51912 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752802AbXGCD2i (ORCPT ); Mon, 2 Jul 2007 23:28:38 -0400 In-Reply-To: <20070703011019.GQ989688@sgi.com> Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Tue, 3 Jul 2007 11:10:19 +1000 David Chinner wrote: > Teach do_mpage_readpage() about unwritten extents so we can > always map them in get_blocks rather than they are are holes on > read. Allows setup_swap_extents() to use preallocated files on XFS > filesystems for swap files without ever needing to convert them. > > Signed-Off-By: Dave Chinner > > --- > fs/mpage.c | 5 +++-- > fs/xfs/linux-2.6/xfs_aops.c | 13 +++---------- > 2 files changed, 6 insertions(+), 12 deletions(-) > > Index: 2.6.x-xfs-new/fs/mpage.c > =================================================================== > --- 2.6.x-xfs-new.orig/fs/mpage.c 2007-05-29 16:17:59.000000000 +1000 > +++ 2.6.x-xfs-new/fs/mpage.c 2007-06-27 22:39:35.568852270 +1000 > @@ -207,7 +207,8 @@ do_mpage_readpage(struct bio *bio, struc > * Map blocks using the result from the previous get_blocks call first. > */ > nblocks = map_bh->b_size >> blkbits; > - if (buffer_mapped(map_bh) && block_in_file > *first_logical_block && > + if (buffer_mapped(map_bh) && !buffer_unwritten(map_bh) && > + block_in_file > *first_logical_block && > block_in_file < (*first_logical_block + nblocks)) { > unsigned map_offset = block_in_file - *first_logical_block; > unsigned last = nblocks - map_offset; > @@ -242,7 +243,7 @@ do_mpage_readpage(struct bio *bio, struc > *first_logical_block = block_in_file; > } > > - if (!buffer_mapped(map_bh)) { > + if (!buffer_mapped(map_bh) || buffer_unwritten(map_bh)) { > fully_mapped = 0; > if (first_hole == blocks_per_page) > first_hole = page_block; > Index: 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_aops.c > =================================================================== > --- 2.6.x-xfs-new.orig/fs/xfs/linux-2.6/xfs_aops.c 2007-06-05 22:14:39.000000000 +1000 > +++ 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_aops.c 2007-06-27 22:39:29.545636749 +1000 > @@ -1340,16 +1340,9 @@ __xfs_get_blocks( > return 0; > > if (iomap.iomap_bn != IOMAP_DADDR_NULL) { > - /* > - * For unwritten extents do not report a disk address on > - * the read case (treat as if we're reading into a hole). > - */ > - if (create || !(iomap.iomap_flags & IOMAP_UNWRITTEN)) { > - xfs_map_buffer(bh_result, &iomap, offset, > - inode->i_blkbits); > - } > - if (create && (iomap.iomap_flags & IOMAP_UNWRITTEN)) { > - if (direct) > + xfs_map_buffer(bh_result, &iomap, offset, inode->i_blkbits); > + if (iomap.iomap_flags & IOMAP_UNWRITTEN) { > + if (create && direct) > bh_result->b_private = inode; > set_buffer_unwritten(bh_result); > } Seems sane, although one does wonder whether it's a worthy tradeoff. We add additional overhead to readpage[s]() just to avoid some IO during mkswap? Also, I wonder what ext4 does in this situation?