nilfs2: separate wait function from nilfs_segctor_write

This separates wait function for submitted logs from the write
function nilfs_segctor_write().  A new list of segment buffers
"sc_write_logs" is added to hold logs under writing, and double
buffering is partially applied to hide io latency.

At this point, the double buffering is disabled for blocksize <
pagesize because page dirty flag is turned off during write and dirty
buffers are not properly collected for pages crossing over segments.

To receive full benefit of the double buffering, further refinement is
needed to move the io wait outside the lock section of log writer.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/nilfs2/segment.h b/fs/nilfs2/segment.h
index 0d2a475a741b..3d3ab2f9864c 100644
--- a/fs/nilfs2/segment.h
+++ b/fs/nilfs2/segment.h
@@ -97,6 +97,7 @@ struct nilfs_segsum_pointer {
  * @sc_dsync_start: start byte offset of data pages
  * @sc_dsync_end: end byte offset of data pages (inclusive)
  * @sc_segbufs: List of segment buffers
+ * @sc_write_logs: List of segment buffers to hold logs under writing
  * @sc_segbuf_nblocks: Number of available blocks in segment buffers.
  * @sc_curseg: Current segment buffer
  * @sc_super_root: Pointer to the super root buffer
@@ -143,6 +144,7 @@ struct nilfs_sc_info {
 
 	/* Segment buffers */
 	struct list_head	sc_segbufs;
+	struct list_head	sc_write_logs;
 	unsigned long		sc_segbuf_nblocks;
 	struct nilfs_segment_buffer *sc_curseg;
 	struct buffer_head     *sc_super_root;