ext4: Fix small file fragmentation

For small file block allocations, mballoc uses per cpu prealloc
space.  Use goal block when searching for the right prealloc
space.  Also make sure ext4_da_writepages tries to write
all the pages for small files in single attempt

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, 15 insertions, 6 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d1906d9a22de..7e91913e325b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2282,13 +2282,12 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode)
 static int ext4_da_writepages(struct address_space *mapping,
                               struct writeback_control *wbc)
 {
-        struct inode *inode = mapping->host;
         handle_t *handle = NULL;
-        int needed_blocks;
-        int ret = 0;
-        long to_write;
         loff_t range_start = 0;
-        long pages_skipped = 0;
+        struct inode *inode = mapping->host;
+        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);
 
         /*
          * No pages to write? This is mainly a kludge to avoid starting
@@ -2297,6 +2296,16 @@ static int ext4_da_writepages(struct address_space *mapping,
          */
         if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
                 return 0;
+        /*
+         * Make sure nr_to_write is >= sbi->s_mb_stream_request
+         * This make sure small files blocks are allocated in
+         * single attempt. This ensure that small files
+         * get less fragmented.
+         */
+        if (wbc->nr_to_write < sbi->s_mb_stream_request) {
+                nr_to_writebump = sbi->s_mb_stream_request - wbc->nr_to_write;
+                wbc->nr_to_write = sbi->s_mb_stream_request;
+        }
 
         if (!wbc->range_cyclic)
                 /*
@@ -2377,7 +2386,7 @@ restart_loop:
         }
 
 out_writepages:
-        wbc->nr_to_write = to_write;
+        wbc->nr_to_write = to_write - nr_to_writebump;
         wbc->range_start = range_start;
         return ret;
 }