Btrfs: Optimize compressed writeback and reads

When reading compressed extents, try to put pages into the page cache
for any pages covered by the compressed extent that readpages didn't already
preload.

Add an async work queue to handle transformations at delayed allocation processing
time.  Right now this is just compression.  The workflow is:

1) Find offsets in the file marked for delayed allocation
2) Lock the pages
3) Lock the state bits
4) Call the async delalloc code

The async delalloc code clears the state lock bits and delalloc bits.  It is
important this happens before the range goes into the work queue because
otherwise it might deadlock with other work queue items that try to lock
those extent bits.

The file pages are compressed, and if the compression doesn't work the
pages are written back directly.

An ordered work queue is used to make sure the inodes are written in the same
order that pdflush or writepages sent them down.

This changes extent_write_cache_pages to let the writepage function
update the wbc nr_written count.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 370bb4285597..027ad6b3839e 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -390,7 +390,7 @@ void btrfs_start_ordered_extent(struct inode *inode,
          * start IO on any dirty ones so the wait doesn't stall waiting
          * for pdflush to find them
          */
-        btrfs_fdatawrite_range(inode->i_mapping, start, end, WB_SYNC_NONE);
+        btrfs_fdatawrite_range(inode->i_mapping, start, end, WB_SYNC_ALL);
         if (wait) {
                 wait_event(entry->wait, test_bit(BTRFS_ORDERED_COMPLETE,
                                                  &entry->flags));
@@ -421,6 +421,12 @@ again:
          */
         btrfs_fdatawrite_range(inode->i_mapping, start, orig_end, WB_SYNC_NONE);
 
+        /* The compression code will leave pages locked but return from
+         * writepage without setting the page writeback.  Starting again
+         * with WB_SYNC_ALL will end up waiting for the IO to actually start.
+         */
+        btrfs_fdatawrite_range(inode->i_mapping, start, orig_end, WB_SYNC_ALL);
+
         btrfs_wait_on_page_writeback_range(inode->i_mapping,
                                            start >> PAGE_CACHE_SHIFT,
                                            orig_end >> PAGE_CACHE_SHIFT);
@@ -448,10 +454,7 @@ again:
         }
         if (test_range_bit(&BTRFS_I(inode)->io_tree, start, orig_end,
                            EXTENT_ORDERED | EXTENT_DELALLOC, 0)) {
-                printk("inode %lu still ordered or delalloc after wait "
-                       "%llu %llu\n", inode->i_ino,
-                       (unsigned long long)start,
-                       (unsigned long long)orig_end);
+                schedule_timeout(1);
                 goto again;
         }
         return 0;