From: Josef Bacik <josef@toxicpanda.com>
Date: Tue, 26 Nov 2019 11:25:54 -0500
Subject: btrfs: kill min_allocable_bytes in inc_block_group_ro
Git-commit: f8935566372c579cf9076d344a76e7781365c6e3
Patch-mainline: v5.6-rc1
References: bsc#1178897

This is a relic from a time before we had a proper reservation mechanism
and you could end up with really full chunks at chunk allocation time.
This doesn't make sense anymore, so just kill it.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/block-group.c |   22 ++++------------------
 1 file changed, 4 insertions(+), 18 deletions(-)

--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1173,21 +1173,8 @@ static int inc_block_group_ro(struct btr
 	struct btrfs_space_info *sinfo = cache->space_info;
 	u64 num_bytes;
 	u64 sinfo_used;
-	u64 min_allocable_bytes;
 	int ret = -ENOSPC;
 
-	/*
-	 * We need some metadata space and system metadata space for
-	 * allocating chunks in some corner cases until we force to set
-	 * it to be readonly.
-	 */
-	if ((sinfo->flags &
-	     (BTRFS_BLOCK_GROUP_SYSTEM | BTRFS_BLOCK_GROUP_METADATA)) &&
-	    !force)
-		min_allocable_bytes = SZ_1M;
-	else
-		min_allocable_bytes = 0;
-
 	spin_lock(&sinfo->lock);
 	spin_lock(&cache->lock);
 
@@ -1205,10 +1192,9 @@ static int inc_block_group_ro(struct btr
 	 * sinfo_used + num_bytes should always <= sinfo->total_bytes.
 	 *
 	 * Here we make sure if we mark this bg RO, we still have enough
-	 * free space as buffer (if min_allocable_bytes is not 0).
+	 * free space as buffer.
 	 */
-	if (sinfo_used + num_bytes + min_allocable_bytes <=
-	    sinfo->total_bytes) {
+	if (sinfo_used + num_bytes <= sinfo->total_bytes) {
 		sinfo->bytes_readonly += num_bytes;
 		cache->ro++;
 		list_add_tail(&cache->ro_list, &sinfo->ro_bgs);
@@ -1222,8 +1208,8 @@ out:
 			"unable to make block group %llu ro",
 			cache->key.objectid);
 		btrfs_info(cache->fs_info,
-			"sinfo_used=%llu bg_num_bytes=%llu min_allocable=%llu",
-			sinfo_used, num_bytes, min_allocable_bytes);
+			"sinfo_used=%llu bg_num_bytes=%llu",
+			sinfo_used, num_bytes);
 		btrfs_dump_space_info(cache->fs_info, cache->space_info, 0, 0);
 	}
 	return ret;