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Wong" Cc: John Garry , linux-ext4@vger.kernel.org, Theodore Ts'o , Jan Kara , Christoph Hellwig , Ojaswin Mujoo , Dave Chinner , linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 1/6] ext4: Add statx support for atomic writes In-Reply-To: <20241025160942.GJ2386201@frogsfrogsfrogs> Date: Fri, 25 Oct 2024 23:15:55 +0530 Message-ID: <87o738m5yk.fsf@gmail.com> References: <314835ec-98bf-472c-8be7-0b26e50cfc9b@oracle.com> <87y12cmr5o.fsf@gmail.com> <20241025160942.GJ2386201@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: "Darrick J. Wong" writes: > On Fri, Oct 25, 2024 at 03:38:03PM +0530, Ritesh Harjani wrote: >> John Garry 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 >> >> Signed-off-by: Ojaswin Mujoo >> >> Signed-off-by: Ritesh Harjani (IBM) >> >> --- >> >> 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; >> >> } >> >> >> >> +/* >>