GFS2: Optimise writepage for metadata

This adds a GFS2 specific writepage for metadata, rather than
continuing to use the VFS function. As a result we now tag all
our metadata I/O with the correct flag so that blktraces will
now be less confusing.

Also, the generic function was checking for a number of corner
cases which cannot happen on the metadata address spaces so that
this should be faster too.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 57 insertions, 9 deletions

diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index 75b2aec06f85..78a5f4312667 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -33,17 +33,65 @@
 #include "util.h"
 #include "ops_address.h"
 
-static int aspace_get_block(struct inode *inode, sector_t lblock,
-                            struct buffer_head *bh_result, int create)
+static int gfs2_aspace_writepage(struct page *page, struct writeback_control *wbc)
 {
-        gfs2_assert_warn(inode->i_sb->s_fs_info, 0);
-        return -EOPNOTSUPP;
-}
+        int err;
+        struct buffer_head *bh, *head;
+        int nr_underway = 0;
+        int write_op = (1 << BIO_RW_META) | ((wbc->sync_mode == WB_SYNC_ALL ?
+                        WRITE_SYNC_PLUG : WRITE));
+
+        BUG_ON(!PageLocked(page));
+        BUG_ON(!page_has_buffers(page));
+
+        head = page_buffers(page);
+        bh = head;
+
+        do {
+                if (!buffer_mapped(bh))
+                        continue;
+                /*
+                 * If it's a fully non-blocking write attempt and we cannot
+                 * lock the buffer then redirty the page.  Note that this can
+                 * potentially cause a busy-wait loop from pdflush and kswapd
+                 * activity, but those code paths have their own higher-level
+                 * throttling.
+                 */
+                if (wbc->sync_mode != WB_SYNC_NONE || !wbc->nonblocking) {
+                        lock_buffer(bh);
+                } else if (!trylock_buffer(bh)) {
+                        redirty_page_for_writepage(wbc, page);
+                        continue;
+                }
+                if (test_clear_buffer_dirty(bh)) {
+                        mark_buffer_async_write(bh);
+                } else {
+                        unlock_buffer(bh);
+                }
+        } while ((bh = bh->b_this_page) != head);
+
+        /*
+         * The page and its buffers are protected by PageWriteback(), so we can
+         * drop the bh refcounts early.
+         */
+        BUG_ON(PageWriteback(page));
+        set_page_writeback(page);
+
+        do {
+                struct buffer_head *next = bh->b_this_page;
+                if (buffer_async_write(bh)) {
+                        submit_bh(write_op, bh);
+                        nr_underway++;
+                }
+                bh = next;
+        } while (bh != head);
+        unlock_page(page);
 
-static int gfs2_aspace_writepage(struct page *page,
-                                 struct writeback_control *wbc)
-{
-        return block_write_full_page(page, aspace_get_block, wbc);
+        err = 0;
+        if (nr_underway == 0)
+                end_page_writeback(page);
+
+        return err;
 }
 
 static const struct address_space_operations aspace_aops = {