On Tue, Oct 24, 2023 at 08:44:14AM +0200, Christoph Hellwig wrote:
> folio_wait_stable waits for writeback to finish before modifying the
> contents of a folio again, e.g. to support check summing of the data
> in the block integrity code.
>
> Currently this behavior is controlled by the SB_I_STABLE_WRITES flag
> on the super_block, which means it is uniform for the entire file system.
> This is wrong for the block device pseudofs which is shared by all
> block devices, or file systems that can use multiple devices like XFS
> witht the RT subvolume or btrfs (although btrfs currently reimplements
> folio_wait_stable anyway).
>
> Add a per-address_space AS_STABLE_WRITES flag to control the behavior
> in a more fine grained way. The existing SB_I_STABLE_WRITES is kept
> to initialize AS_STABLE_WRITES to the existing default which covers
> most cases.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/inode.c | 2 ++
> include/linux/pagemap.h | 17 +++++++++++++++++
> mm/page-writeback.c | 2 +-
For a hot second I wondered if we could get rid of SB_I_STABLE_WRITES
too, but then had an AHA moment when I saw that NFS also sets it.
This looks reasonable,
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> 3 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/fs/inode.c b/fs/inode.c
> index 84bc3c76e5ccb5..ae1a6410b53d7e 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -215,6 +215,8 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
> lockdep_set_class_and_name(&mapping->invalidate_lock,
> &sb->s_type->invalidate_lock_key,
> "mapping.invalidate_lock");
> + if (sb->s_iflags & SB_I_STABLE_WRITES)
> + mapping_set_stable_writes(mapping);
> inode->i_private = NULL;
> inode->i_mapping = mapping;
> INIT_HLIST_HEAD(&inode->i_dentry); /* buggered by rcu freeing */
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 351c3b7f93a14e..8c9608b217b000 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -204,6 +204,8 @@ enum mapping_flags {
> AS_NO_WRITEBACK_TAGS = 5,
> AS_LARGE_FOLIO_SUPPORT = 6,
> AS_RELEASE_ALWAYS, /* Call ->release_folio(), even if no private data */
> + AS_STABLE_WRITES, /* must wait for writeback before modifying
> + folio contents */
> };
>
> /**
> @@ -289,6 +291,21 @@ static inline void mapping_clear_release_always(struct address_space *mapping)
> clear_bit(AS_RELEASE_ALWAYS, &mapping->flags);
> }
>
> +static inline bool mapping_stable_writes(const struct address_space *mapping)
> +{
> + return test_bit(AS_STABLE_WRITES, &mapping->flags);
> +}
> +
> +static inline void mapping_set_stable_writes(struct address_space *mapping)
> +{
> + set_bit(AS_STABLE_WRITES, &mapping->flags);
> +}
> +
> +static inline void mapping_clear_stable_writes(struct address_space *mapping)
> +{
> + clear_bit(AS_STABLE_WRITES, &mapping->flags);
> +}
> +
> static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
> {
> return mapping->gfp_mask;
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index b8d3d7040a506a..4656534b8f5cc6 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -3110,7 +3110,7 @@ EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);
> */
> void folio_wait_stable(struct folio *folio)
> {
> - if (folio_inode(folio)->i_sb->s_iflags & SB_I_STABLE_WRITES)
> + if (mapping_stable_writes(folio_mapping(folio)))
> folio_wait_writeback(folio);
> }
> EXPORT_SYMBOL_GPL(folio_wait_stable);
> --
> 2.39.2
>
