ext4: Adjust ext4_da_writepages() to write out larger contiguous chunks

Work around problems in the writeback code to force out writebacks in
larger chunks than just 4mb, which is just too small.  This also works
around limitations in the ext4 block allocator, which can't allocate
more than 2048 blocks at a time.  So we need to defeat the round-robin
characteristics of the writeback code and try to write out as many
blocks in one inode before allowing the writeback code to move on to
another inode.  We add a a new per-filesystem tunable,
max_writeback_mb_bump, which caps this to a default of 128mb per
inode.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index e227eea23f0..a58438e18d0 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -942,6 +942,7 @@ struct ext4_sb_info {
 	unsigned int s_mb_stats;
 	unsigned int s_mb_order2_reqs;
 	unsigned int s_mb_group_prealloc;
+	unsigned int s_max_writeback_mb_bump;
 	/* where last allocation was done - for stream allocation */
 	unsigned long s_mb_last_group;
 	unsigned long s_mb_last_start;