Re: [RFC PATCH] mm/khugepaged: free empty xa_nodes when rollbacks in collapse_file

[Jinjiang Tu <tujinjiang@huawei.com>]

在 2026/1/21 14:38, Matthew Wilcox 写道:
> On Wed, Jan 21, 2026 at 02:22:43PM +0800, Jinjiang Tu wrote:
>> collapse_file() calls xas_create_range() to pre-create all slots needed.
>> If collapse_file() finally fails, these pre-created slots are empty nodes
>> and aren't destroyed.
> try this instead
>
> diff --git a/fs/inode.c b/fs/inode.c
> index cff1d3af0d57..85886af1e7ab 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -744,22 +744,18 @@ void dump_mapping(const struct address_space *mapping)
>   
>   void clear_inode(struct inode *inode)
>   {
> -	/*
> -	 * We have to cycle the i_pages lock here because reclaim can be in the
> -	 * process of removing the last page (in __filemap_remove_folio())
> -	 * and we must not free the mapping under it.
> -	 */
> -	xa_lock_irq(&inode->i_data.i_pages);
> -	BUG_ON(inode->i_data.nrpages);
>   	/*
>   	 * Almost always, mapping_empty(&inode->i_data) here; but there are
>   	 * two known and long-standing ways in which nodes may get left behind
>   	 * (when deep radix-tree node allocation failed partway; or when THP
> -	 * collapse_file() failed). Until those two known cases are cleaned up,
> -	 * or a cleanup function is called here, do not BUG_ON(!mapping_empty),
> -	 * nor even WARN_ON(!mapping_empty).
> +	 * collapse_file() failed).
> +	 *
> +	 * xa_destroy() also cycles the lock for us, which is needed because
> +	 * reclaim can be in the process of removing the last folio (in
> +	 * __filemap_remove_folio()) and we must not free the mapping under it.
>   	 */
> -	xa_unlock_irq(&inode->i_data.i_pages);
> +	xa_destroy(&inode->i_data.i_pages);
> +	BUG_ON(inode->i_data.nrpages);
>   	BUG_ON(!list_empty(&inode->i_data.i_private_list));
>   	BUG_ON(!(inode->i_state & I_FREEING));
>   	BUG_ON(inode->i_state & I_CLEAR);

Hi, Matthew

This appoach is much simpler. Could you please send a formal patch?