[Ocfs2-devel] [PATCH] ocfs2: lighten up allocate transaction

[Younger Liu]

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
Jul  3 19:42:08 linux-KooNDD kernel: [ 7372.278591] JBD: fallocate wants too many credits (2051 > 2048)
Jul  3 19:42:08 linux-KooNDD kernel: [ 7372.278597] (fallocate,6438,0):__ocfs2_extend_allocation:709 ERROR: status = -12
Jul  3 19:42:08 linux-KooNDD kernel: [ 7372.278603] (fallocate,6438,0):ocfs2_allocate_unwritten_extents:1504 ERROR: status = -12
Jul  3 19:42:08 linux-KooNDD kernel: [ 7372.278607] (fallocate,6438,0):__ocfs2_change_file_space:1955 ERROR: status = -12
^C

With this patch, the test works well.

Signed-off-by: Younger Liu <younger.liu at huawei.com>
---
 fs/ocfs2/file.c    |    6 +-----
 fs/ocfs2/journal.c |   34 ++++++++++++++++++++++++++++++++++
 fs/ocfs2/journal.h |   11 +++++++++++
 3 files changed, 46 insertions(+), 5 deletions(-)

diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index 05c0bb1..4943918 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -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. */
diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
index 8eccfab..501b2fe 100644
--- a/fs/ocfs2/journal.c
+++ b/fs/ocfs2/journal.c
@@ -455,6 +455,40 @@ 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.
+ * Refer extend_or_restart_transaction() 
+ */
+int ocfs2_allocate_extend_trans(handle_t *handle, int thresh)
+{
+	int status;
+
+	BUG_ON(!handle);
+	
+	if (handle->h_buffer_credits < thresh)
+		return 0;
+
+	status = jbd2_journal_extend(handle, OCFS2_MAX_TRANS_DATA);
+	if (status < 0) {
+		mlog_errno(status);
+		goto bail;
+	}
+
+	if (status > 0) {
+		status = jbd2_journal_restart(handle, OCFS2_MAX_TRANS_DATA);
+		if (status < 0) {
+			mlog_errno(status);
+			goto bail;
+		}
+	}
+	
+bail:
+	return status;
+}
+
+
 struct ocfs2_triggers {
 	struct jbd2_buffer_trigger_type	ot_triggers;
 	int				ot_offset;
diff --git a/fs/ocfs2/journal.h b/fs/ocfs2/journal.h
index a3385b6..62a26bd 100644
--- a/fs/ocfs2/journal.h
+++ b/fs/ocfs2/journal.h
@@ -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
-- 
1.7.9.7