writeback: split writeback_inodes_wb

The case where we have a superblock doesn't require a loop here as we scan
over all inodes in writeback_sb_inodes. Split it out into a separate helper
to make the code simpler.  This also allows to get rid of the sb member in
struct writeback_control, which was rather out of place there.

Also update the comments in writeback_sb_inodes that explain the handling
of inodes from wrong superblocks.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 94a602e..8cc06d5 100644 (file)
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -554,29 +554,41 @@ static bool pin_sb_for_writeback(struct super_block *sb)
 
 /*
  * Write a portion of b_io inodes which belong to @sb.
- * If @wbc->sb != NULL, then find and write all such
+ *
+ * If @only_this_sb is true, then find and write all such
  * inodes. Otherwise write only ones which go sequentially
  * in reverse order.
+ *
  * Return 1, if the caller writeback routine should be
  * interrupted. Otherwise return 0.
  */
-static int writeback_sb_inodes(struct super_block *sb,
-                              struct bdi_writeback *wb,
-                              struct writeback_control *wbc)
+static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
+               struct writeback_control *wbc, bool only_this_sb)
 {
        while (!list_empty(&wb->b_io)) {
                long pages_skipped;
                struct inode *inode = list_entry(wb->b_io.prev,
                                                 struct inode, i_list);
-               if (wbc->sb && sb != inode->i_sb) {
-                       /* super block given and doesn't
-                          match, skip this inode */
-                       redirty_tail(inode);
-                       continue;
-               }
-               if (sb != inode->i_sb)
-                       /* finish with this superblock */
+
+               if (inode->i_sb != sb) {
+                       if (only_this_sb) {
+                               /*
+                                * We only want to write back data for this
+                                * superblock, move all inodes not belonging
+                                * to it back onto the dirty list.
+                                */
+                               redirty_tail(inode);
+                               continue;
+                       }
+
+                       /*
+                        * The inode belongs to a different superblock.
+                        * Bounce back to the caller to unpin this and
+                        * pin the next superblock.
+                        */
                        return 0;
+               }
+
                if (inode->i_state & (I_NEW | I_WILL_FREE)) {
                        requeue_io(inode);
                        continue;
@@ -629,29 +641,12 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
                                                 struct inode, i_list);
                struct super_block *sb = inode->i_sb;
 
-               if (wbc->sb) {
-                       /*
-                        * We are requested to write out inodes for a specific
-                        * superblock.  This means we already have s_umount
-                        * taken by the caller which also waits for us to
-                        * complete the writeout.
-                        */
-                       if (sb != wbc->sb) {
-                               redirty_tail(inode);
-                               continue;
-                       }
-
-                       WARN_ON(!rwsem_is_locked(&sb->s_umount));
-
-                       ret = writeback_sb_inodes(sb, wb, wbc);
-               } else {
-                       if (!pin_sb_for_writeback(sb)) {
-                               requeue_io(inode);
-                               continue;
-                       }
-                       ret = writeback_sb_inodes(sb, wb, wbc);
-                       drop_super(sb);
+               if (!pin_sb_for_writeback(sb)) {
+                       requeue_io(inode);
+                       continue;
                }
+               ret = writeback_sb_inodes(sb, wb, wbc, false);
+               drop_super(sb);
 
                if (ret)
                        break;
@@ -660,6 +655,19 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
        /* Leave any unwritten inodes on b_io */
 }
 
+static void __writeback_inodes_sb(struct super_block *sb,
+               struct bdi_writeback *wb, struct writeback_control *wbc)
+{
+       WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+       wbc->wb_start = jiffies; /* livelock avoidance */
+       spin_lock(&inode_lock);
+       if (!wbc->for_kupdate || list_empty(&wb->b_io))
+               queue_io(wb, wbc->older_than_this);
+       writeback_sb_inodes(sb, wb, wbc, true);
+       spin_unlock(&inode_lock);
+}
+
 /*
  * The maximum number of pages to writeout in a single bdi flush/kupdate
  * operation.  We do this so we don't hold I_SYNC against an inode for
@@ -698,7 +706,6 @@ static long wb_writeback(struct bdi_writeback *wb,
                         struct wb_writeback_args *args)
 {
        struct writeback_control wbc = {
-               .sb                     = args->sb,
                .sync_mode              = args->sync_mode,
                .older_than_this        = NULL,
                .for_kupdate            = args->for_kupdate,
@@ -736,7 +743,10 @@ static long wb_writeback(struct bdi_writeback *wb,
                wbc.more_io = 0;
                wbc.nr_to_write = MAX_WRITEBACK_PAGES;
                wbc.pages_skipped = 0;
-               writeback_inodes_wb(wb, &wbc);
+               if (args->sb)
+                       __writeback_inodes_sb(args->sb, wb, &wbc);
+               else
+                       writeback_inodes_wb(wb, &wbc);
                args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
                wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index f6756f6..c24eca7 100644 (file)
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -27,8 +27,6 @@ enum writeback_sync_modes {
  * in a manner such that unspecified fields are set to zero.
  */
 struct writeback_control {
-       struct super_block *sb;         /* if !NULL, only write inodes from
-                                          this super_block */
        enum writeback_sync_modes sync_mode;
        unsigned long *older_than_this; /* If !NULL, only write back inodes
                                           older than this */