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Message-ID: <rperz6ny5wjhhtmxrpnqtju64g33erxxi4rvho5gslqonzy5gb@uwbqxdjycw4y>
Date: Mon, 24 Feb 2025 15:27:27 +0100
From: Jan Kara <jack@...e.cz>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc: linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ext4: Make sb update interval tunable
On Sat 22-02-25 14:10:23, Ojaswin Mujoo wrote:
> Currently, outside error paths, we auto commit the super block after 1
> hour has passed and 16MB worth of updates have been written since last
> commit. This is a policy decision so make this tunable while keeping the
> defaults same. This is useful if user wants to tweak the superblock
> update behavior or for debugging the codepath by allowing to trigger it
> more frequently.
>
> We can now tweak the super block update using sb_update_sec and
> sb_update_kb files in /sys/fs/ext4/<dev>/
>
> Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Looks sensible. Feel free to add:
Reviewed-by: Jan Kara <jack@...e.cz>
Honza
> ---
> fs/ext4/ext4.h | 9 +++++++++
> fs/ext4/super.c | 15 ++++++++-------
> fs/ext4/sysfs.c | 4 ++++
> 3 files changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 2b7d781bfcad..306e5db7129c 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1608,6 +1608,8 @@ struct ext4_sb_info {
> unsigned int s_mb_prefetch;
> unsigned int s_mb_prefetch_limit;
> unsigned int s_mb_best_avail_max_trim_order;
> + unsigned int s_sb_update_sec;
> + unsigned int s_sb_update_kb;
>
> /* stats for buddy allocator */
> atomic_t s_bal_reqs; /* number of reqs with len > 1 */
> @@ -2279,6 +2281,13 @@ static inline int ext4_forced_shutdown(struct super_block *sb)
> #define EXT4_DEF_MIN_BATCH_TIME 0
> #define EXT4_DEF_MAX_BATCH_TIME 15000 /* 15ms */
>
> +/*
> + * Default values for superblock update
> + */
> +#define EXT4_DEF_SB_UPDATE_INTERVAL_SEC (3600) /* seconds (1 hour) */
> +#define EXT4_DEF_SB_UPDATE_INTERVAL_KB (16384) /* kilobytes (16MB) */
> +
> +
> /*
> * Minimum number of groups in a flexgroup before we separate out
> * directories into the first block group of a flexgroup
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index b7341e9acf62..129d666f450b 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -447,9 +447,6 @@ static time64_t __ext4_get_tstamp(__le32 *lo, __u8 *hi)
> #define ext4_get_tstamp(es, tstamp) \
> __ext4_get_tstamp(&(es)->tstamp, &(es)->tstamp ## _hi)
>
> -#define EXT4_SB_REFRESH_INTERVAL_SEC (3600) /* seconds (1 hour) */
> -#define EXT4_SB_REFRESH_INTERVAL_KB (16384) /* kilobytes (16MB) */
> -
> /*
> * The ext4_maybe_update_superblock() function checks and updates the
> * superblock if needed.
> @@ -457,8 +454,10 @@ static time64_t __ext4_get_tstamp(__le32 *lo, __u8 *hi)
> * This function is designed to update the on-disk superblock only under
> * certain conditions to prevent excessive disk writes and unnecessary
> * waking of the disk from sleep. The superblock will be updated if:
> - * 1. More than an hour has passed since the last superblock update, and
> - * 2. More than 16MB have been written since the last superblock update.
> + * 1. More than sbi->s_sb_update_sec (def: 1 hour) has passed since the last
> + * superblock update
> + * 2. More than sbi->s_sb_update_kb (def: 16MB) kbs have been written since the
> + * last superblock update.
> *
> * @sb: The superblock
> */
> @@ -479,7 +478,7 @@ static void ext4_maybe_update_superblock(struct super_block *sb)
> now = ktime_get_real_seconds();
> last_update = ext4_get_tstamp(es, s_wtime);
>
> - if (likely(now - last_update < EXT4_SB_REFRESH_INTERVAL_SEC))
> + if (likely(now - last_update < sbi->s_sb_update_sec))
> return;
>
> lifetime_write_kbytes = sbi->s_kbytes_written +
> @@ -494,7 +493,7 @@ static void ext4_maybe_update_superblock(struct super_block *sb)
> */
> diff_size = lifetime_write_kbytes - le64_to_cpu(es->s_kbytes_written);
>
> - if (diff_size > EXT4_SB_REFRESH_INTERVAL_KB)
> + if (diff_size > sbi->s_sb_update_kb)
> schedule_work(&EXT4_SB(sb)->s_sb_upd_work);
> }
>
> @@ -5248,6 +5247,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
> sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
> sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
> sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;
> + sbi->s_sb_update_kb = EXT4_DEF_SB_UPDATE_INTERVAL_KB;
> + sbi->s_sb_update_sec = EXT4_DEF_SB_UPDATE_INTERVAL_SEC;
>
> /*
> * set default s_li_wait_mult for lazyinit, for the case there is
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index ddb54608ca2e..987bd00f916a 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -254,6 +254,8 @@ EXT4_ATTR(journal_task, 0444, journal_task);
> EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch);
> EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit);
> EXT4_RW_ATTR_SBI_UL(last_trim_minblks, s_last_trim_minblks);
> +EXT4_RW_ATTR_SBI_UI(sb_update_sec, s_sb_update_sec);
> +EXT4_RW_ATTR_SBI_UI(sb_update_kb, s_sb_update_kb);
>
> static unsigned int old_bump_val = 128;
> EXT4_ATTR_PTR(max_writeback_mb_bump, 0444, pointer_ui, &old_bump_val);
> @@ -305,6 +307,8 @@ static struct attribute *ext4_attrs[] = {
> ATTR_LIST(mb_prefetch),
> ATTR_LIST(mb_prefetch_limit),
> ATTR_LIST(last_trim_minblks),
> + ATTR_LIST(sb_update_sec),
> + ATTR_LIST(sb_update_kb),
> NULL,
> };
> ATTRIBUTE_GROUPS(ext4);
> --
> 2.48.1
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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