On 2019/11/25 下午10:40, Josef Bacik wrote:
> 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.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  fs/btrfs/block-group.c | 22 ++++------------------
>  1 file changed, 4 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> index 6934a5b8708f..db539bfc5a52 100644
> --- a/fs/btrfs/block-group.c
> +++ b/fs/btrfs/block-group.c
> @@ -1185,21 +1185,8 @@ static int inc_block_group_ro(struct btrfs_block_group *cache, int force)
>  	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);
>  
> @@ -1217,10 +1204,9 @@ static int inc_block_group_ro(struct btrfs_block_group *cache, int force)
>  	 * 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) {

I guess it's a typo.

It should be "if (sinfo_used + num_bytes <= sinfo->total_bytes) {"

Although the last patch will remove the check, it's still better to keep
each patch works fine to make bisect easier.

Thanks,
Qu

>  		sinfo->bytes_readonly += num_bytes;
>  		cache->ro++;
>  		list_add_tail(&cache->ro_list, &sinfo->ro_bgs);
> @@ -1233,8 +1219,8 @@ static int inc_block_group_ro(struct btrfs_block_group *cache, int force)
>  		btrfs_info(cache->fs_info,
>  			"unable to make block group %llu ro", cache->start);
>  		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;
>