On Fri, Oct 25, 2024 at 03:38:03PM +0530, Ritesh Harjani wrote:
> John Garry <john.g.garry@xxxxxxxxxx> writes:
>
> > On 25/10/2024 04:45, Ritesh Harjani (IBM) wrote:
> >> This patch adds base support for atomic writes via statx getattr.
> >> On bs < ps systems, we can create FS with say bs of 16k. That means
> >> both atomic write min and max unit can be set to 16k for supporting
> >> atomic writes.
> >>
> >> Later patches adds support for bigalloc as well so that ext4 can also
> >> support doing atomic writes for bs = ps systems.
> >>
> >> Co-developed-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
> >> Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
> >> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
> >> ---
> >> fs/ext4/ext4.h | 7 ++++++-
> >> fs/ext4/inode.c | 14 ++++++++++++++
> >> fs/ext4/super.c | 32 ++++++++++++++++++++++++++++++++
> >> 3 files changed, 52 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> >> index 44b0d418143c..a41e56c2c628 100644
> >> --- a/fs/ext4/ext4.h
> >> +++ b/fs/ext4/ext4.h
> >> @@ -1729,6 +1729,10 @@ struct ext4_sb_info {
> >> */
> >> struct work_struct s_sb_upd_work;
> >>
> >> + /* Atomic write unit values */
> >> + unsigned int fs_awu_min;
> >> + unsigned int fs_awu_max;
> >> +
> >> /* Ext4 fast commit sub transaction ID */
> >> atomic_t s_fc_subtid;
> >>
> >> @@ -1820,7 +1824,8 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
> >> */
> >> enum {
> >> EXT4_MF_MNTDIR_SAMPLED,
> >> - EXT4_MF_FC_INELIGIBLE /* Fast commit ineligible */
> >> + EXT4_MF_FC_INELIGIBLE, /* Fast commit ineligible */
> >> + EXT4_MF_ATOMIC_WRITE /* Supports atomic write */
> >
> > Does this flag really buy us much?
> >
>
> I felt it is cleaner this way than comparing non-zero values of
> fs_awu_min and fs_awu_max.
What does it mean when MF_ATOMIC_WRITE is set and fs_awu_* are zero?
The awu values don't change at runtime, so I think you can save yourself
an atomic test by checking (non-atomically) for awu_min>0.
(I don't know anything about the flags, those came after my time iirc.)
--D
> Now that you pointed at it - Maybe a question for others who might have
> the history of which one to use when - or do we think there is a scope
> of merging the two into just one as a later cleanup?
>
> I know that s_mount_flags was added for fastcommit and it needed the
> state manipulations to be done in atomic way. Similarly s_ext4_flags
> also was renamed from s_resize_flags for more general purpose use. Both
> of these looks like could be merged isn't it?
>
>
>
> >> };
> >>
> >> static inline void ext4_set_mount_flag(struct super_block *sb, int bit)
> >> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> >> index 54bdd4884fe6..897c028d5bc9 100644
> >> --- a/fs/ext4/inode.c
> >> +++ b/fs/ext4/inode.c
> >> @@ -5578,6 +5578,20 @@ int ext4_getattr(struct mnt_idmap *idmap, const struct path *path,
> >> }
> >> }
> >>
> >> + if (S_ISREG(inode->i_mode) && (request_mask & STATX_WRITE_ATOMIC)) {
> >> + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> >> + unsigned int awu_min, awu_max;
> >> +
> >> + if (ext4_test_mount_flag(inode->i_sb, EXT4_MF_ATOMIC_WRITE)) {
> >
> > I'd use ext4_inode_can_atomicwrite() here, similar to what is done for xfs
> >
>
> Sure since it is inode operation, we can check against ext4_inode_can_atomicwrite().
>
>
> >> + awu_min = sbi->fs_awu_min;
> >> + awu_max = sbi->fs_awu_max;
> >> + } else {
> >> + awu_min = awu_max = 0;
> >> + }
> >> +
> >> + generic_fill_statx_atomic_writes(stat, awu_min, awu_max);
> >> + }
> >> +
> >> flags = ei->i_flags & EXT4_FL_USER_VISIBLE;
> >> if (flags & EXT4_APPEND_FL)
> >> stat->attributes |= STATX_ATTR_APPEND;
> >> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> >> index 16a4ce704460..f5c075aff060 100644
> >> --- a/fs/ext4/super.c
> >> +++ b/fs/ext4/super.c
> >> @@ -4425,6 +4425,37 @@ static int ext4_handle_clustersize(struct super_block *sb)
> >> return 0;
> >> }
> >>
> >> +/*
>
