On Wed, Feb 20, 2013 at 8:10 AM, Liu Bo <bo.li.liu@xxxxxxxxxx> wrote:
> Right now inode cache inode is treated as the same as space cache
> inode, ie. keep inode in memory till putting super.
>
> But this leads to an awkward situation.
>
> If we're going to delete a snapshot/subvolume, btrfs will not
> actually delete it and return free space, but will add it to dead
> roots list until the last inode on this snap/subvol being destroyed.
> Then we'll fetch deleted roots and cleanup them via cleaner thread.
>
> So here is the problem, if we enable inode cache option, each
> snap/subvol has a cached inode which is used to store inode allcation
> information. And this cache inode will be kept in memory, as the above
> said. So with inode cache, snap/subvol can only be added into
> dead roots list during freeing roots stage in umount, so that we can
> ONLY get space back after another remount(we cleanup dead roots on mount).
>
> But the real thing is we'll no more use the snap/subvol if we mark it
> deleted, so we can safely iput its cache inode when we delete snap/subvol.
>
> Another thing is that we need to change the rules of droping inode, we
> don't keep snap/subvol's cache inode in memory till end so that we can
> add snap/subvol into dead roots list in time.
>
> Reported-by: Mitch Harder <mitch.harder@xxxxxxxxxxxxxxxx>
> Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> ---
> fs/btrfs/inode.c | 3 ++-
> fs/btrfs/ioctl.c | 6 ++++++
> 2 files changed, 8 insertions(+), 1 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index ca7ace7..d9984fa 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -7230,8 +7230,9 @@ int btrfs_drop_inode(struct inode *inode)
> {
> struct btrfs_root *root = BTRFS_I(inode)->root;
>
> + /* the snap/subvol tree is on deleting */
> if (btrfs_root_refs(&root->root_item) == 0 &&
> - !btrfs_is_free_space_inode(inode))
> + root != root->fs_info->tree_root)
> return 1;
> else
> return generic_drop_inode(inode);
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index a31cd93..375f31f 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2171,6 +2171,12 @@ out_unlock:
> shrink_dcache_sb(root->fs_info->sb);
> btrfs_invalidate_inodes(dest);
> d_delete(dentry);
> +
> + /* the last ref */
> + if (dest->cache_inode) {
> + iput(dest->cache_inode);
> + dest->cache_inode = NULL;
> + }
> }
> out_dput:
> dput(dentry);
> --
> 1.7.7.6
>
Thanks, I tested this patch, and it fixes the issues I was seeing.
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