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Message-ID: <39b6d2b2-77fd-4087-a495-c36d33b8c9d0@oracle.com>
Date: Tue, 29 Oct 2024 08:54:53 +0000
From: John Garry <john.g.garry@...cle.com>
To: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>, linux-ext4@...r.kernel.org
Cc: Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>,
"Darrick J . Wong" <djwong@...nel.org>,
Christoph Hellwig
<hch@...radead.org>,
Ojaswin Mujoo <ojaswin@...ux.ibm.com>,
Dave Chinner <david@...morbit.com>, linux-kernel@...r.kernel.org,
linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] ext4: Add statx support for atomic writes
On 27/10/2024 18:17, 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.
>
> Co-developed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
> ---
> fs/ext4/ext4.h | 9 +++++++++
> fs/ext4/inode.c | 14 ++++++++++++++
> fs/ext4/super.c | 31 +++++++++++++++++++++++++++++++
> 3 files changed, 54 insertions(+)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 44b0d418143c..6ee49aaacd2b 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 in bytes */
> + unsigned int s_awu_min;
> + unsigned int s_awu_max;
> +
> /* Ext4 fast commit sub transaction ID */
> atomic_t s_fc_subtid;
>
> @@ -3855,6 +3859,11 @@ static inline int ext4_buffer_uptodate(struct buffer_head *bh)
> return buffer_uptodate(bh);
> }
>
> +static inline bool ext4_can_atomic_write(struct super_block *sb)
> +{
> + return EXT4_SB(sb)->s_awu_min > 0;
> +}
> +
> extern int ext4_block_write_begin(handle_t *handle, struct folio *folio,
> loff_t pos, unsigned len,
> get_block_t *get_block);
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 54bdd4884fe6..fcdee27b9aa2 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_can_atomic_write(inode->i_sb)) {
> + awu_min = sbi->s_awu_min;
> + awu_max = sbi->s_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..d6e3201a48be 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4425,6 +4425,36 @@ static int ext4_handle_clustersize(struct super_block *sb)
> return 0;
> }
>
> +/*
> + * ext4_atomic_write_init: Initializes filesystem min & max atomic write units.
> + * @sb: super block
> + * TODO: Later add support for bigalloc
> + */
> +static void ext4_atomic_write_init(struct super_block *sb)
> +{
> + struct ext4_sb_info *sbi = EXT4_SB(sb);
> + struct block_device *bdev = sb->s_bdev;
> +
> + if (!bdev_can_atomic_write(bdev))
this check is duplicated, since bdev_atomic_write_unit_{min,
max}_bytes() has this check
> + return;
> +
> + if (!ext4_has_feature_extents(sb))
> + return;
> +
> + sbi->s_awu_min = max(sb->s_blocksize,
> + bdev_atomic_write_unit_min_bytes(bdev));
> + sbi->s_awu_max = min(sb->s_blocksize,
> + bdev_atomic_write_unit_max_bytes(bdev));
> + if (sbi->s_awu_min && sbi->s_awu_max &&
> + sbi->s_awu_min <= sbi->s_awu_max) {
This looks a bit complicated. I would just follow the XFS example and
ensure bdev_atomic_write_unit_min_bytes() <= sb->s_blocksize <=
bdev_atomic_write_unit_max_bytes() [which you are doing, but in a
complicated way]
> + ext4_msg(sb, KERN_NOTICE, "Supports atomic writes awu_min: %u, awu_max: %u",
> + sbi->s_awu_min, sbi->s_awu_max);
> + } else {
> + sbi->s_awu_min = 0;
> + sbi->s_awu_max = 0;
> + }
> +}
> +
> static void ext4_fast_commit_init(struct super_block *sb)
> {
> struct ext4_sb_info *sbi = EXT4_SB(sb);
> @@ -5336,6 +5366,7 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>
> spin_lock_init(&sbi->s_bdev_wb_lock);
>
> + ext4_atomic_write_init(sb);
> ext4_fast_commit_init(sb);
>
> sb->s_root = NULL;
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