GFS2: rewrite fallocate code to write blocks directly

GFS2's fallocate code currently goes through the page cache. Since it's only
writing to the end of the file or to holes in it, it doesn't need to, and it
was causing issues on low memory environments. This patch pulls in some of
Steve's block allocation work, and uses it to simply allocate the blocks for
the file, and zero them out at allocation time.  It provides a slight
performance increase, and it dramatically simplifies the code.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 24 insertions, 147 deletions

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index aa3a4dd..5002408 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -669,135 +669,18 @@ static ssize_t gfs2_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	return generic_file_aio_write(iocb, iov, nr_segs, pos);
 }
 
-static int empty_write_end(struct page *page, unsigned from,
-			   unsigned to, int mode)
-{
-	struct inode *inode = page->mapping->host;
-	struct gfs2_inode *ip = GFS2_I(inode);
-	struct buffer_head *bh;
-	unsigned offset, blksize = 1 << inode->i_blkbits;
-	pgoff_t end_index = i_size_read(inode) >> PAGE_CACHE_SHIFT;
-
-	zero_user(page, from, to-from);
-	mark_page_accessed(page);
-
-	if (page->index < end_index || !(mode & FALLOC_FL_KEEP_SIZE)) {
-		if (!gfs2_is_writeback(ip))
-			gfs2_page_add_databufs(ip, page, from, to);
-
-		block_commit_write(page, from, to);
-		return 0;
-	}
-
-	offset = 0;
-	bh = page_buffers(page);
-	while (offset < to) {
-		if (offset >= from) {
-			set_buffer_uptodate(bh);
-			mark_buffer_dirty(bh);
-			clear_buffer_new(bh);
-			write_dirty_buffer(bh, WRITE);
-		}
-		offset += blksize;
-		bh = bh->b_this_page;
-	}
-
-	offset = 0;
-	bh = page_buffers(page);
-	while (offset < to) {
-		if (offset >= from) {
-			wait_on_buffer(bh);
-			if (!buffer_uptodate(bh))
-				return -EIO;
-		}
-		offset += blksize;
-		bh = bh->b_this_page;
-	}
-	return 0;
-}
-
-static int needs_empty_write(sector_t block, struct inode *inode)
-{
-	int error;
-	struct buffer_head bh_map = { .b_state = 0, .b_blocknr = 0 };
-
-	bh_map.b_size = 1 << inode->i_blkbits;
-	error = gfs2_block_map(inode, block, &bh_map, 0);
-	if (unlikely(error))
-		return error;
-	return !buffer_mapped(&bh_map);
-}
-
-static int write_empty_blocks(struct page *page, unsigned from, unsigned to,
-			      int mode)
-{
-	struct inode *inode = page->mapping->host;
-	unsigned start, end, next, blksize;
-	sector_t block = page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
-	int ret;
-
-	blksize = 1 << inode->i_blkbits;
-	next = end = 0;
-	while (next < from) {
-		next += blksize;
-		block++;
-	}
-	start = next;
-	do {
-		next += blksize;
-		ret = needs_empty_write(block, inode);
-		if (unlikely(ret < 0))
-			return ret;
-		if (ret == 0) {
-			if (end) {
-				ret = __block_write_begin(page, start, end - start,
-							  gfs2_block_map);
-				if (unlikely(ret))
-					return ret;
-				ret = empty_write_end(page, start, end, mode);
-				if (unlikely(ret))
-					return ret;
-				end = 0;
-			}
-			start = next;
-		}
-		else
-			end = next;
-		block++;
-	} while (next < to);
-
-	if (end) {
-		ret = __block_write_begin(page, start, end - start, gfs2_block_map);
-		if (unlikely(ret))
-			return ret;
-		ret = empty_write_end(page, start, end, mode);
-		if (unlikely(ret))
-			return ret;
-	}
-
-	return 0;
-}
-
 static int fallocate_chunk(struct inode *inode, loff_t offset, loff_t len,
 			   int mode)
 {
 	struct gfs2_inode *ip = GFS2_I(inode);
 	struct buffer_head *dibh;
 	int error;
-	u64 start = offset >> PAGE_CACHE_SHIFT;
-	unsigned int start_offset = offset & ~PAGE_CACHE_MASK;
-	u64 end = (offset + len - 1) >> PAGE_CACHE_SHIFT;
-	pgoff_t curr;
-	struct page *page;
-	unsigned int end_offset = (offset + len) & ~PAGE_CACHE_MASK;
-	unsigned int from, to;
-
-	if (!end_offset)
-		end_offset = PAGE_CACHE_SIZE;
+	unsigned int nr_blks;
+	sector_t lblock = offset >> inode->i_blkbits;
 
 	error = gfs2_meta_inode_buffer(ip, &dibh);
 	if (unlikely(error))
-		goto out;
+		return error;
 
 	gfs2_trans_add_bh(ip->i_gl, dibh, 1);
 
@@ -807,39 +690,31 @@ static int fallocate_chunk(struct inode *inode, loff_t offset, loff_t len,
 			goto out;
 	}
 
-	curr = start;
-	offset = start << PAGE_CACHE_SHIFT;
-	from = start_offset;
-	to = PAGE_CACHE_SIZE;
-	while (curr <= end) {
-		page = grab_cache_page_write_begin(inode->i_mapping, curr,
-						   AOP_FLAG_NOFS);
-		if (unlikely(!page)) {
-			error = -ENOMEM;
-			goto out;
-		}
+	while (len) {
+		struct buffer_head bh_map = { .b_state = 0, .b_blocknr = 0 };
+		bh_map.b_size = len;
+		set_buffer_zeronew(&bh_map);
 
-		if (curr == end)
-			to = end_offset;
-		error = write_empty_blocks(page, from, to, mode);
-		if (!error && offset + to > inode->i_size &&
-		    !(mode & FALLOC_FL_KEEP_SIZE)) {
-			i_size_write(inode, offset + to);
-		}
-		unlock_page(page);
-		page_cache_release(page);
-		if (error)
+		error = gfs2_block_map(inode, lblock, &bh_map, 1);
+		if (unlikely(error))
 			goto out;
-		curr++;
-		offset += PAGE_CACHE_SIZE;
-		from = 0;
+		len -= bh_map.b_size;
+		nr_blks = bh_map.b_size >> inode->i_blkbits;
+		lblock += nr_blks;
+		if (!buffer_new(&bh_map))
+			continue;
+		if (unlikely(!buffer_zeronew(&bh_map))) {
+			error = -EIO;
+			goto out;
+		}
 	}
+	if (offset + len > inode->i_size && !(mode & FALLOC_FL_KEEP_SIZE))
+		i_size_write(inode, offset + len);
 
 	mark_inode_dirty(inode);
 
-	brelse(dibh);
-
 out:
+	brelse(dibh);
 	return error;
 }
 
@@ -879,6 +754,7 @@ static long gfs2_fallocate(struct file *file, int mode, loff_t offset,
 	int error;
 	loff_t bsize_mask = ~((loff_t)sdp->sd_sb.sb_bsize - 1);
 	loff_t next = (offset + len - 1) >> sdp->sd_sb.sb_bsize_shift;
+	loff_t max_chunk_size = UINT_MAX & bsize_mask;
 	next = (next + 1) << sdp->sd_sb.sb_bsize_shift;
 
 	/* We only support the FALLOC_FL_KEEP_SIZE mode */
@@ -932,7 +808,8 @@ retry:
 			goto out_qunlock;
 		}
 		max_bytes = bytes;
-		calc_max_reserv(ip, len, &max_bytes, &data_blocks, &ind_blocks);
+		calc_max_reserv(ip, (len > max_chunk_size)? max_chunk_size: len,
+				&max_bytes, &data_blocks, &ind_blocks);
 		al->al_requested = data_blocks + ind_blocks;
 
 		rblocks = RES_DINODE + ind_blocks + RES_STATFS + RES_QUOTA +