ext4: rework reserved cluster accounting when invalidating pages

The goal of this patch is to remove two references to the buffer delay
bit in ext4_da_page_release_reservation() as part of a larger effort
to remove all such references from ext4.  These two references are
principally used to reduce the reserved block/cluster count when pages
are invalidated as a result of truncating, punching holes, or
collapsing a block range in a file.  The entire function is removed
and replaced with code in ext4_es_remove_extent() that reduces the
reserved count as a side effect of removing a block range from delayed
and not unwritten extents in the extent status tree as is done when
truncating, punching holes, or collapsing ranges.

The code is written to minimize the number of searches descending from
rb tree roots for scalability.
Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -284,6 +284,9 @@ struct ext4_io_submit {
 				  ~((ext4_fsblk_t) (s)->s_cluster_ratio - 1))
 #define EXT4_LBLK_CMASK(s, lblk) ((lblk) &				\
 				  ~((ext4_lblk_t) (s)->s_cluster_ratio - 1))
+/* Fill in the low bits to get the last block of the cluster */
+#define EXT4_LBLK_CFILL(sbi, lblk) ((lblk) |				\
+				    ((ext4_lblk_t) (sbi)->s_cluster_ratio - 1))
 /* Get the cluster offset */
 #define EXT4_PBLK_COFF(s, pblk) ((pblk) &				\
 				 ((ext4_fsblk_t) (s)->s_cluster_ratio - 1))

fs/ext4/extents_status.h

@@ -247,8 +247,6 @@ extern int ext4_es_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk,
 					bool allocated);
 extern unsigned int ext4_es_delayed_clu(struct inode *inode, ext4_lblk_t lblk,
 					ext4_lblk_t len);
-extern void ext4_es_remove_blks(struct inode *inode, ext4_lblk_t lblk,
-				ext4_lblk_t len);
 extern void ext4_clear_inode_es(struct inode *inode);
 
 #endif /* _EXT4_EXTENTS_STATUS_H */

fs/ext4/inode.c

@@ -1646,49 +1646,6 @@ void ext4_da_release_space(struct inode *inode, int to_free)
 	dquot_release_reservation_block(inode, EXT4_C2B(sbi, to_free));
 }
 
-static void ext4_da_page_release_reservation(struct page *page,
-					     unsigned int offset,
-					     unsigned int length)
-{
-	int contiguous_blks = 0;
-	struct buffer_head *head, *bh;
-	unsigned int curr_off = 0;
-	struct inode *inode = page->mapping->host;
-	unsigned int stop = offset + length;
-	ext4_fsblk_t lblk;
-
-	BUG_ON(stop > PAGE_SIZE || stop < length);
-
-	head = page_buffers(page);
-	bh = head;
-	do {
-		unsigned int next_off = curr_off + bh->b_size;
-
-		if (next_off > stop)
-			break;
-
-		if ((offset <= curr_off) && (buffer_delay(bh))) {
-			contiguous_blks++;
-			clear_buffer_delay(bh);
-		} else if (contiguous_blks) {
-			lblk = page->index <<
-			       (PAGE_SHIFT - inode->i_blkbits);
-			lblk += (curr_off >> inode->i_blkbits) -
-				contiguous_blks;
-			ext4_es_remove_blks(inode, lblk, contiguous_blks);
-			contiguous_blks = 0;
-		}
-		curr_off = next_off;
-	} while ((bh = bh->b_this_page) != head);
-
-	if (contiguous_blks) {
-		lblk = page->index << (PAGE_SHIFT - inode->i_blkbits);
-		lblk += (curr_off >> inode->i_blkbits) - contiguous_blks;
-		ext4_es_remove_blks(inode, lblk, contiguous_blks);
-	}
-
-}
-
 /*
  * Delayed allocation stuff
  */
@@ -3227,24 +3184,6 @@ static int ext4_da_write_end(struct file *file,
 	return ret ? ret : copied;
 }
 
-static void ext4_da_invalidatepage(struct page *page, unsigned int offset,
-				   unsigned int length)
-{
-	/*
-	 * Drop reserved blocks
-	 */
-	BUG_ON(!PageLocked(page));
-	if (!page_has_buffers(page))
-		goto out;
-
-	ext4_da_page_release_reservation(page, offset, length);
-
-out:
-	ext4_invalidatepage(page, offset, length);
-
-	return;
-}
-
 /*
  * Force all delayed allocation blocks to be allocated for a given inode.
  */
@@ -3985,7 +3924,7 @@ static const struct address_space_operations ext4_da_aops = {
 	.write_end		= ext4_da_write_end,
 	.set_page_dirty		= ext4_set_page_dirty,
 	.bmap			= ext4_bmap,
-	.invalidatepage		= ext4_da_invalidatepage,
+	.invalidatepage		= ext4_invalidatepage,
 	.releasepage		= ext4_releasepage,
 	.direct_IO		= ext4_direct_IO,
 	.migratepage		= buffer_migrate_page,