Re: [PATCH v2 08/18] btrfs: extent_io: support subpage for extent buffer page release

[Nikolay Borisov <nborisov@suse.com>]

On 10.12.20 г. 8:38 ч., Qu Wenruo wrote:
> In btrfs_release_extent_buffer_pages(), we need to add extra handling
> for subpage.
> 
> To do so, introduce a new helper, detach_extent_buffer_page(), to do
> different handling for regular and subpage cases.
> 
> For subpage case, the new trick is to clear the range of current extent
> buffer, and detach page private if and only if we're the last tree block
> of the page.
> This part is handled by the subpage helper,
> btrfs_subpage_clear_and_test_tree_block().
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/extent_io.c | 59 +++++++++++++++++++++++++++++++-------------
>  fs/btrfs/subpage.h   | 24 ++++++++++++++++++
>  2 files changed, 66 insertions(+), 17 deletions(-)

<snip>

> @@ -5031,6 +5018,44 @@ static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
>  			 */
>  			detach_page_private(page);
>  		}
> +		return;
> +	}
> +
> +	/*
> +	 * For subpage case, clear the range in tree_block_bitmap,
> +	 * and if we're the last one, detach private completely.
> +	 */
> +	if (PagePrivate(page)) {

Under what condition can you have subpage fs and call
detach_extent_buffer_page on a page that doesn't have PagePrivate flag
set ?  I think that's impossible i.e that check should be really an assert?

> +		bool last = false;
> +
> +		last = btrfs_subpage_clear_and_test_tree_block(fs_info, page,
> +						eb->start, eb->len);
> +		if (last)
> +			btrfs_detach_subpage(fs_info, page);
> +	}
> +}
> +


<snip>