jbd2: Completely fill journal descriptor blocks

With 32-bit block numbers, we don't allocate the array for journal
buffer heads large enough for corresponding descriptor tags to fill the
descriptor block. Thus we end up writing out half-full descriptor blocks
to the journal unnecessarily growing the transaction. Fix the logic to
allocate the array large enough.

Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20191105164437.32602-3-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 1c58859aa59245506b3cea0b5f955434f167a1f5..cc11097f117668ce9cf6b31a96fc62d5a547a0d2 100644 (file)
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1098,6 +1098,16 @@ static void jbd2_stats_proc_exit(journal_t *journal)
        remove_proc_entry(journal->j_devname, proc_jbd2_stats);
 }
 
+/* Minimum size of descriptor tag */
+static int jbd2_min_tag_size(void)
+{
+       /*
+        * Tag with 32-bit block numbers does not use last four bytes of the
+        * structure
+        */
+       return sizeof(journal_block_tag_t) - 4;
+}
+
 /*
  * Management for journal control blocks: functions to create and
  * destroy journal_t structures, and to initialise and read existing
@@ -1156,7 +1166,8 @@ static journal_t *journal_init_common(struct block_device *bdev,
        journal->j_fs_dev = fs_dev;
        journal->j_blk_offset = start;
        journal->j_maxlen = len;
-       n = journal->j_blocksize / sizeof(journal_block_tag_t);
+       /* We need enough buffers to write out full descriptor block. */
+       n = journal->j_blocksize / jbd2_min_tag_size();
        journal->j_wbufsize = n;
        journal->j_wbuf = kmalloc_array(n, sizeof(struct buffer_head *),
                                        GFP_KERNEL);