ocfs2: lighten up allocate transaction

The issue scenario is as following:
When fallocating a very large disk space for a small file, __ocfs2_extend_allocation attempts to get a very large transaction. For some journal sizes, there may be not enough room for this transaction, and the fallocate will fail.

The patch below extents & restarts the transaction as necessary while allocating space, and should work with even the smallest journal. This patch refers ext4 resize.

Test:

# mkfs.ocfs2 -b 4K -C 32K -T datafiles /dev/sdc
...(jounral size is 32M)
# mount.ocfs2 /dev/sdc /mnt/ocfs2/
# touch /mnt/ocfs2/1.log
# fallocate -o 0 -l 400G /mnt/ocfs2/1.log
fallocate: /mnt/ocfs2/1.log: fallocate failed: Cannot allocate memory
# tail -f /var/log/messages
[ 7372.278591] JBD: fallocate wants too many credits (2051 > 2048)
[ 7372.278597] (fallocate,6438,0):__ocfs2_extend_allocation:709 ERROR: status = -12
[ 7372.278603] (fallocate,6438,0):ocfs2_allocate_unwritten_extents:1504 ERROR: status = -12
[ 7372.278607] (fallocate,6438,0):__ocfs2_change_file_space:1955 ERROR: status = -12
^C

With this patch, the test works well.

Compared with V1, add trace point in ocfs2_allocate_extend_trans.

Signed-off-by Younger Liu <[email protected]>

Cc Jie Liu <[email protected]>

---
 fs/ocfs2/file.c        |    6 +-----
 fs/ocfs2/journal.c     |   36 ++++++++++++++++++++++++++++++++++++
 fs/ocfs2/journal.h     |   11 +++++++++++
 fs/ocfs2/ocfs2_trace.h |    2 ++
 4 files changed, 50 insertions(+), 5 deletions(-)

fs/ocfs2/file.c +1 -5

index 05c0bb1..4943918 100644
@@ -666,11 +666,7 @@ restarted_transaction:
 		} else {
 			BUG_ON(why != RESTART_TRANS);
 
-			/* TODO: This can be more intelligent. */
-			credits = ocfs2_calc_extend_credits(osb->sb,
-							    &fe->id2.i_list,
-							    clusters_to_add);
-			status = ocfs2_extend_trans(handle, credits);
+			status = ocfs2_allocate_extend_trans(handle, 1);
 			if (status < 0) {
 				/* handle still has to be committed at
 				 * this point. */

fs/ocfs2/journal.c +20 -0

index 8eccfab..1d389fb 100644
@@ -455,6 +455,42 @@ bail:
 	return status;
 }
 
+/*
+ * If we have fewer than thresh credits, extend by OCFS2_MAX_TRANS_DATA.
+ * If that fails, restart the transaction & regain write access for the
+ * buffer head which is used for metadata modifications.
+ * Taken from Ext4: extend_or_restart_transaction() 
+ */
+int ocfs2_allocate_extend_trans(handle_t *handle, int thresh)
+{
+	int status, old_nblks;
+
+	BUG_ON(!handle);
+	
+	old_nblks = handle->h_buffer_credits;
+	trace_ocfs2_allocate_extend_trans(old_nblks, thresh);
+	
+	if (old_nblks < thresh)
+		return 0;
+
+	status = jbd2_journal_extend(handle, OCFS2_MAX_TRANS_DATA);
+	if (status < 0) {

fs/ocfs2/journal.c +6 -0

+	}
+	
+bail:
+	return status;
+}
+
 struct ocfs2_triggers {
 	struct jbd2_buffer_trigger_type	ot_triggers;
 	int				ot_offset;

fs/ocfs2/journal.h +11 -0

index a3385b6..62a26bd 100644
@@ -259,6 +259,17 @@ handle_t		    *ocfs2_start_trans(struct ocfs2_super *osb,
 int			     ocfs2_commit_trans(struct ocfs2_super *osb,
 						handle_t *handle);
 int			     ocfs2_extend_trans(handle_t *handle, int nblocks);
+int			     ocfs2_allocate_extend_trans(handle_t *handle,
+						int thresh);
+
+/* 
+ * Define an arbitrary limit for the amount of data we will anticipate
+ * writing to any given transaction.  For unbounded transactions such as
+ * fallocate(2) we can write more than this, but we always
+ * start off at the maximum transaction size and grow the transaction
+ * optimistically as we go.
+ */
+#define OCFS2_MAX_TRANS_DATA	64U
 
 /*
  * Create access is for when we get a newly created buffer and we're

fs/ocfs2/ocfs2_trace.h +2 -0

index 3b481f4..1b60c62 100644
@@ -2579,6 +2579,8 @@ DEFINE_OCFS2_INT_INT_EVENT(ocfs2_extend_trans);
 
 DEFINE_OCFS2_INT_EVENT(ocfs2_extend_trans_restart);
 
+DEFINE_OCFS2_INT_INT_EVENT(ocfs2_allocate_extend_trans);
+
 DEFINE_OCFS2_ULL_ULL_UINT_UINT_EVENT(ocfs2_journal_access);
 
 DEFINE_OCFS2_ULL_EVENT(ocfs2_journal_dirty);