Re: [PATCH 1/2] btrfs: implement launder_folio for clearing dirty page rsv

[Qu Wenruo <wqu@suse.com>]

在 2024/7/24 08:25, Boris Burkov 写道:
> In the buffered write path, dirty pages can be said to "own" the qgroup
> reservation until they create an ordered_extent. It is possible for
> there to be outstanding dirty pages when a transaction is aborted, in
> which case there is no cancellation path for freeing this reservation
> and it is leaked.
> 
> We do already walk the list of outstanding delalloc inodes in
> btrfs_destroy_delalloc_inodes and call invalidate_inode_pages2 on them.
> 
> This does *not* call btrfs_invalidate_folio, as one might guess, but
> rather calls launder_folio and release_folio. Since this is a
> reservation associated with dirty pages only, rather than something
> associated with the private bit (ordered_extent is cancelled separately
> already in the cleanup txn path), implementing this release should be
> done via launder_folio.

Well, the launder_folio() is completely new to me.

But indeed invalidate_inode_pages2_range() calls folio_launder() then
invalidate_complete_folio2() -> filemap_release_folio() -> 
btrfs_release_folio().

Thus we lack the handling for such cases.

> 
> Signed-off-by: Boris Burkov <boris@bur.io>

Reviewed-by: Qu Wenruo <wqu@suse.com>

Thanks,
Qu
> ---
>   fs/btrfs/inode.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 8f38eefc8acd..c5155981f99a 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -7198,6 +7198,11 @@ static void wait_subpage_spinlock(struct page *page)
>   	spin_unlock_irq(&subpage->lock);
>   }
>   
> +static int btrfs_launder_folio(struct folio *folio)
> +{
> +	return btrfs_qgroup_free_data(folio_to_inode(folio), NULL, folio_pos(folio), PAGE_SIZE, NULL);
> +}
> +
>   static bool __btrfs_release_folio(struct folio *folio, gfp_t gfp_flags)
>   {
>   	if (try_release_extent_mapping(&folio->page, gfp_flags)) {
> @@ -10133,6 +10138,7 @@ static const struct address_space_operations btrfs_aops = {
>   	.writepages	= btrfs_writepages,
>   	.readahead	= btrfs_readahead,
>   	.invalidate_folio = btrfs_invalidate_folio,
> +	.launder_folio	= btrfs_launder_folio,
>   	.release_folio	= btrfs_release_folio,
>   	.migrate_folio	= btrfs_migrate_folio,
>   	.dirty_folio	= filemap_dirty_folio,