Btrfs: rework how we reserve metadata bytes

With multi-threaded writes we were getting ENOSPC early because somebody would
come in, start flushing delalloc because they couldn't make their reservation,
and in the meantime other threads would come in and use the space that was
getting freed up, so when the original thread went to check to see if they had
space they didn't and they'd return ENOSPC.  So instead if we have some free
space but not enough for our reservation, take the reservation and then start
doing the flushing.  The only time we don't take reservations is when we've
already overcommitted our space, that way we don't have people who come late to
the party way overcommitting ourselves.  This also moves all of the retrying and
flushing code into reserve_metdata_bytes so it's all uniform.  This keeps my
fs_mark test from returning -ENOSPC as soon as it starts and actually lets me
fill up the disk.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 2 insertions, 5 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 66e4c66cc63b..abbec80aaa44 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -179,7 +179,6 @@ static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
 {
         struct btrfs_trans_handle *h;
         struct btrfs_transaction *cur_trans;
-        int retries = 0;
         int ret;
 again:
         h = kmem_cache_alloc(btrfs_trans_handle_cachep, GFP_NOFS);
@@ -212,8 +211,7 @@ again:
         }
 
         if (num_items > 0) {
-                ret = btrfs_trans_reserve_metadata(h, root, num_items,
-                                                   &retries);
+                ret = btrfs_trans_reserve_metadata(h, root, num_items);
                 if (ret == -EAGAIN) {
                         btrfs_commit_transaction(h, root);
                         goto again;
@@ -836,7 +834,6 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
         struct extent_buffer *tmp;
         struct extent_buffer *old;
         int ret;
-        int retries = 0;
         u64 to_reserve = 0;
         u64 index = 0;
         u64 objectid;
@@ -858,7 +855,7 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
 
         if (to_reserve > 0) {
                 ret = btrfs_block_rsv_add(trans, root, &pending->block_rsv,
-                                          to_reserve, &retries);
+                                          to_reserve);
                 if (ret) {
                         pending->error = ret;
                         goto fail;