Re: [PATCH 3/8] btrfs: move the root freeing stuff into btrfs_put_root

From: Nikolay Borisov <nborisov@suse.com>
To: Josef Bacik <josef@toxicpanda.com>,
	linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH 3/8] btrfs: move the root freeing stuff into btrfs_put_root
Date: Wed, 19 Feb 2020 17:10:16 +0200	[thread overview]
Message-ID: <058f94f8-7fb6-9dfb-61e0-21dc989e22bc@suse.com> (raw)
In-Reply-To: <20200214211147.24610-4-josef@toxicpanda.com>

On 14.02.20 г. 23:11 ч., Josef Bacik wrote:
> There are a few different ways to free roots, either you allocated them
> yourself and you just do
> 
> free_extent_buffer(root->node);
> free_extent_buffer(root->commit_node);
> btrfs_put_root(root);
> 
> Which is the pattern for log roots.  Or for snapshots/subvolumes that
> are being dropped you simply call btrfs_free_fs_root() which does all
> the cleanup for you.
> 
> Unify this all into btrfs_put_root(), so that we don't free up things
> associated with the root until the last reference is dropped.  This
> makes the root freeing code much more significant.
> 
> The only caveat is at close_ctree() time we have to free the extent
> buffers for all of our main roots (extent_root, chunk_root, etc) because
> we have to drop the btree_inode and we'll run into issues if we hold
> onto those nodes until ->kill_sb() time.  This will be addressed in the
> future when we kill the btree_inode.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

Nit: This patch obsoleted the last comment in btrfs_init_fs_root, namely:

/* The caller is responsible to call btrfs_free_fs_root */

> ---
>  fs/btrfs/disk-io.c           | 64 ++++++++++++++++++------------------
>  fs/btrfs/disk-io.h           | 16 +--------
>  fs/btrfs/extent-tree.c       |  7 ++--
>  fs/btrfs/extent_io.c         | 16 +++++++--
>  fs/btrfs/free-space-tree.c   |  2 --
>  fs/btrfs/qgroup.c            |  7 +---
>  fs/btrfs/relocation.c        |  4 ---
>  fs/btrfs/tests/btrfs-tests.c |  5 +--
>  fs/btrfs/tree-log.c          |  6 ----
>  9 files changed, 50 insertions(+), 77 deletions(-)
> 

<snip>

> @@ -4795,7 +4803,6 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>  
>  static void __free_extent_buffer(struct extent_buffer *eb)
>  {
> -	btrfs_leak_debug_del(&eb->fs_info->eb_leak_lock, &eb->leak_list);
>  	kmem_cache_free(extent_buffer_cache, eb);
>  }

This function becomes a trivial wrapper so should be eliminated altogether.

<snip>

> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index 034f5f151a74..4fb7e3cc2aca 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -2549,10 +2549,6 @@ void free_reloc_roots(struct list_head *list)
>  		reloc_root = list_entry(list->next, struct btrfs_root,
>  					root_list);
>  		__del_reloc_root(reloc_root);
> -		free_extent_buffer(reloc_root->node);
> -		free_extent_buffer(reloc_root->commit_root);
> -		reloc_root->node = NULL;
> -		reloc_root->commit_root = NULL;

Shouldn't you do btrfs_put_root(reloc_root) here ?

>  	}
>  }
>  

<snip>