"Darrick J. Wong" <djwong@xxxxxxxxxx> writes:
> 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.
Sure. I agree with the reasoning that we can just check for awu_min > 0.
I can write an inline helper for this.
>
> (I don't know anything about the flags, those came after my time iirc.)
>
Thanks for the review :)
-ritesh
> --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;
>> >> }
>> >>
>> >> +/*
>>
