From: Josef Bacik <josef@toxicpanda.com>
Date: Mon, 3 Dec 2018 10:20:36 -0500
Subject: btrfs: rework btrfs_check_space_for_delayed_refs
Git-commit: 64403612b73a94bc7b02cf8ca126e3b8ced6e921
Patch-mainline: v5.0-rc1
References: bsc#1165949

Now with the delayed_refs_rsv we can now know exactly how much pending
delayed refs space we need.  This means we can drastically simplify
btrfs_check_space_for_delayed_refs by simply checking how much space we
have reserved for the global rsv (which acts as a spill over buffer) and
the delayed refs rsv.  If our total size is beyond that amount then we
know it's time to commit the transaction and stop any more delayed refs
from being generated.

With the introduction of dealyed_refs_rsv infrastructure, namely
btrfs_update_delayed_refs_rsv we now know exactly how much pending
delayed refs space is required.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/ctree.h       |    3 +--
 fs/btrfs/extent-tree.c |   49 ++++++++++++++++++-------------------------------
 fs/btrfs/inode.c       |    2 +-
 fs/btrfs/transaction.c |    2 +-
 4 files changed, 21 insertions(+), 35 deletions(-)

--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2650,8 +2650,7 @@ static inline u64 btrfs_calc_trunc_metad
 
 int btrfs_should_throttle_delayed_refs(struct btrfs_trans_handle *trans,
 				       struct btrfs_fs_info *fs_info);
-int btrfs_check_space_for_delayed_refs(struct btrfs_trans_handle *trans,
-				       struct btrfs_fs_info *fs_info);
+bool btrfs_check_space_for_delayed_refs(struct btrfs_fs_info *fs_info);
 void btrfs_dec_block_group_reservations(struct btrfs_fs_info *fs_info,
 					 const u64 start);
 void btrfs_wait_block_group_reservations(struct btrfs_block_group_cache *bg);
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2931,40 +2931,27 @@ u64 btrfs_csum_bytes_to_leaves(struct bt
 	return num_csums;
 }
 
-int btrfs_check_space_for_delayed_refs(struct btrfs_trans_handle *trans,
-				       struct btrfs_fs_info *fs_info)
+bool btrfs_check_space_for_delayed_refs(struct btrfs_fs_info *fs_info)
 {
-	struct btrfs_block_rsv *global_rsv;
-	u64 num_heads = trans->transaction->delayed_refs.num_heads_ready;
-	u64 csum_bytes = trans->transaction->delayed_refs.pending_csums;
-	u64 num_dirty_bgs = trans->transaction->num_dirty_bgs;
-	u64 num_bytes, num_dirty_bgs_bytes;
-	int ret = 0;
-
-	num_bytes = btrfs_calc_trans_metadata_size(fs_info, 1);
-	num_heads = heads_to_leaves(fs_info, num_heads);
-	if (num_heads > 1)
-		num_bytes += (num_heads - 1) * fs_info->nodesize;
-	num_bytes <<= 1;
-	num_bytes += btrfs_csum_bytes_to_leaves(fs_info, csum_bytes) *
-							fs_info->nodesize;
-	num_dirty_bgs_bytes = btrfs_calc_trans_metadata_size(fs_info,
-							     num_dirty_bgs);
-	global_rsv = &fs_info->global_block_rsv;
-
-	/*
-	 * If we can't allocate any more chunks lets make sure we have _lots_ of
-	 * wiggle room since running delayed refs can create more delayed refs.
-	 */
-	if (global_rsv->space_info->full) {
-		num_dirty_bgs_bytes <<= 1;
-		num_bytes <<= 1;
-	}
+	struct btrfs_block_rsv *delayed_refs_rsv = &fs_info->delayed_refs_rsv;
+	struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
+	bool ret = false;
+	u64 reserved;
 
 	spin_lock(&global_rsv->lock);
-	if (global_rsv->reserved <= num_bytes + num_dirty_bgs_bytes)
-		ret = 1;
+	reserved = global_rsv->reserved;
 	spin_unlock(&global_rsv->lock);
+	/*
+	 * Since the global reserve is just kind of magic we don't really want
+	 * to rely on it to save our bacon, so if our size is more than the
+	 * delayed_refs_rsv and the global rsv then it's time to think about
+	 * bailing.
+	 */
+	spin_lock(&delayed_refs_rsv->lock);
+	reserved += delayed_refs_rsv->reserved;
+	if (delayed_refs_rsv->size >= reserved)
+		ret = true;
+	spin_unlock(&delayed_refs_rsv->lock);
 	return ret;
 }
 
@@ -2984,7 +2971,7 @@ int btrfs_should_throttle_delayed_refs(s
 	if (val >= NSEC_PER_SEC / 2)
 		return 2;
 
-	return btrfs_check_space_for_delayed_refs(trans, fs_info);
+	return btrfs_check_space_for_delayed_refs(fs_info);
 }
 
 struct async_delayed_refs {
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5113,7 +5113,7 @@ static struct btrfs_trans_handle *evict_
 		 * Try to steal from the global reserve if there is space for
 		 * it.
 		 */
-		if (!btrfs_check_space_for_delayed_refs(trans, fs_info) &&
+		if (!btrfs_check_space_for_delayed_refs(fs_info) &&
 		    !btrfs_block_rsv_migrate(global_rsv, rsv, rsv->size, 0))
 			return trans;
 
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -828,7 +828,7 @@ static int should_end_transaction(struct
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
 
-	if (btrfs_check_space_for_delayed_refs(trans, fs_info))
+	if (btrfs_check_space_for_delayed_refs(fs_info))
 		return 1;
 
 	return !!btrfs_block_rsv_check(&fs_info->global_block_rsv, 5);