ext4: Fix file fragmentation during large file write.

The range_cyclic writeback mode uses the address_space writeback_index
as the start index for writeback.  With delayed allocation we were
updating writeback_index wrongly resulting in highly fragmented file.
This patch reduces the number of extents reduced from 4000 to 27 for a
3GB file.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 57 insertions, 34 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4ee3f0692eeb..27fc6b951221 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1648,6 +1648,7 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd)
         int ret = 0, err, nr_pages, i;
         unsigned long index, end;
         struct pagevec pvec;
+        long pages_skipped;
 
         BUG_ON(mpd->next_page <= mpd->first_page);
         pagevec_init(&pvec, 0);
@@ -1655,7 +1656,6 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd)
         end = mpd->next_page - 1;
 
         while (index <= end) {
-                /* XXX: optimize tail */
                 /*
                  * We can use PAGECACHE_TAG_DIRTY lookup here because
                  * even though we have cleared the dirty flag on the page
@@ -1673,8 +1673,13 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd)
                 for (i = 0; i < nr_pages; i++) {
                         struct page *page = pvec.pages[i];
 
+                        pages_skipped = mpd->wbc->pages_skipped;
                         err = mapping->a_ops->writepage(page, mpd->wbc);
-                        if (!err)
+                        if (!err && (pages_skipped == mpd->wbc->pages_skipped))
+                                /*
+                                 * have successfully written the page
+                                 * without skipping the same
+                                 */
                                 mpd->pages_written++;
                         /*
                          * In error case, we have to continue because
@@ -2110,7 +2115,6 @@ static int mpage_da_writepages(struct address_space *mapping,
                                struct writeback_control *wbc,
                                struct mpage_da_data *mpd)
 {
-        long to_write;
         int ret;
 
         if (!mpd->get_block)
@@ -2125,19 +2129,18 @@ static int mpage_da_writepages(struct address_space *mapping,
         mpd->pages_written = 0;
         mpd->retval = 0;
 
-        to_write = wbc->nr_to_write;
-
         ret = write_cache_pages(mapping, wbc, __mpage_da_writepage, mpd);
-
         /*
          * Handle last extent of pages
          */
         if (!mpd->io_done && mpd->next_page != mpd->first_page) {
                 if (mpage_da_map_blocks(mpd) == 0)
                         mpage_da_submit_io(mpd);
-        }
 
-        wbc->nr_to_write = to_write - mpd->pages_written;
+                mpd->io_done = 1;
+                ret = MPAGE_DA_EXTENT_TAIL;
+        }
+        wbc->nr_to_write -= mpd->pages_written;
         return ret;
 }
 
@@ -2366,11 +2369,14 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode)
 static int ext4_da_writepages(struct address_space *mapping,
                               struct writeback_control *wbc)
 {
+        pgoff_t index;
+        int range_whole = 0;
         handle_t *handle = NULL;
         struct mpage_da_data mpd;
         struct inode *inode = mapping->host;
+        int no_nrwrite_index_update;
+        long pages_written = 0, pages_skipped;
         int needed_blocks, ret = 0, nr_to_writebump = 0;
-        long to_write, pages_skipped = 0;
         struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
 
         /*
@@ -2390,16 +2396,26 @@ static int ext4_da_writepages(struct address_space *mapping,
                 nr_to_writebump = sbi->s_mb_stream_request - wbc->nr_to_write;
                 wbc->nr_to_write = sbi->s_mb_stream_request;
         }
+        if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
+                range_whole = 1;
 
-
-        pages_skipped = wbc->pages_skipped;
+        if (wbc->range_cyclic)
+                index = mapping->writeback_index;
+        else
+                index = wbc->range_start >> PAGE_CACHE_SHIFT;
 
         mpd.wbc = wbc;
         mpd.inode = mapping->host;
 
-restart_loop:
-        to_write = wbc->nr_to_write;
-        while (!ret && to_write > 0) {
+        /*
+         * we don't want write_cache_pages to update
+         * nr_to_write and writeback_index
+         */
+        no_nrwrite_index_update = wbc->no_nrwrite_index_update;
+        wbc->no_nrwrite_index_update = 1;
+        pages_skipped = wbc->pages_skipped;
+
+        while (!ret && wbc->nr_to_write > 0) {
 
                 /*
                  * we  insert one extent at a time. So we need
@@ -2420,46 +2436,53 @@ restart_loop:
                         dump_stack();
                         goto out_writepages;
                 }
-                to_write -= wbc->nr_to_write;
-
                 mpd.get_block = ext4_da_get_block_write;
                 ret = mpage_da_writepages(mapping, wbc, &mpd);
 
                 ext4_journal_stop(handle);
 
-                if (mpd.retval == -ENOSPC)
+                if (mpd.retval == -ENOSPC) {
+                        /* commit the transaction which would
+                         * free blocks released in the transaction
+                         * and try again
+                         */
                         jbd2_journal_force_commit_nested(sbi->s_journal);
-
-                /* reset the retry count */
-                if (ret == MPAGE_DA_EXTENT_TAIL) {
+                        wbc->pages_skipped = pages_skipped;
+                        ret = 0;
+                } else if (ret == MPAGE_DA_EXTENT_TAIL) {
                         /*
                          * got one extent now try with
                          * rest of the pages
                          */
-                        to_write += wbc->nr_to_write;
+                        pages_written += mpd.pages_written;
+                        wbc->pages_skipped = pages_skipped;
                         ret = 0;
-                } else if (wbc->nr_to_write) {
+                } else if (wbc->nr_to_write)
                         /*
                          * There is no more writeout needed
                          * or we requested for a noblocking writeout
                          * and we found the device congested
                          */
-                        to_write += wbc->nr_to_write;
                         break;
-                }
-                wbc->nr_to_write = to_write;
-        }
-
-        if (!wbc->range_cyclic && (pages_skipped != wbc->pages_skipped)) {
-                /* We skipped pages in this loop */
-                wbc->nr_to_write = to_write +
-                                wbc->pages_skipped - pages_skipped;
-                wbc->pages_skipped = pages_skipped;
-                goto restart_loop;
         }
+        if (pages_skipped != wbc->pages_skipped)
+                printk(KERN_EMERG "This should not happen leaving %s "
+                                "with nr_to_write = %ld ret = %d\n",
+                                __func__, wbc->nr_to_write, ret);
+
+        /* Update index */
+        index += pages_written;
+        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
+                /*
+                 * set the writeback_index so that range_cyclic
+                 * mode will write it back later
+                 */
+                mapping->writeback_index = index;
 
 out_writepages:
-        wbc->nr_to_write = to_write - nr_to_writebump;
+        if (!no_nrwrite_index_update)
+                wbc->no_nrwrite_index_update = 0;
+        wbc->nr_to_write -= nr_to_writebump;
         return ret;
 }