ext4: Retry block reservation

During block reservation if we don't have enough blocks left, retry
block reservation with smaller block counts.  This makes sure we try
fallocate and DIO with smaller request size and don't fail early.  The
delayed allocation reservation cannot try with smaller block count. So
retry block reservation to handle temporary disk full conditions.  Also
print free blocks details if we fail block allocation during writepages.

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

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 2c10b5058a8d..e4f30de11a9d 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4395,7 +4395,12 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
                 /*
                  * With delalloc we already reserved the blocks
                  */
-                if (ext4_claim_free_blocks(sbi, ar->len)) {
+                while (ar->len && ext4_claim_free_blocks(sbi, ar->len)) {
+                        /* let others to free the space */
+                        yield();
+                        ar->len = ar->len >> 1;
+                }
+                if (!ar->len) {
                         *errp = -ENOSPC;
                         return 0;
                 }