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Message-ID: <CALTww29YpgLSzPPkvo79bf5M-pNjGroJrmGBwx2XGQhMOQEe4A@mail.gmail.com>
Date: Mon, 10 Nov 2025 10:30:55 +0800
From: Xiao Ni <xni@...hat.com>
To: linan666@...weicloud.com
Cc: corbet@....net, song@...nel.org, yukuai@...as.com, linan122@...wei.com,
hare@...e.de, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-raid@...r.kernel.org, yangerkun@...wei.com, yi.zhang@...wei.com
Subject: Re: [PATCH v9 5/5] md: allow configuring logical block size
On Mon, Nov 3, 2025 at 9:06 PM <linan666@...weicloud.com> wrote:
>
> From: Li Nan <linan122@...wei.com>
>
> Previously, raid array used the maximum logical block size (LBS)
> of all member disks. Adding a larger LBS disk at runtime could
> unexpectedly increase RAID's LBS, risking corruption of existing
> partitions. This can be reproduced by:
>
> ```
> # LBS of sd[de] is 512 bytes, sdf is 4096 bytes.
> mdadm -CRq /dev/md0 -l1 -n3 /dev/sd[de] missing --assume-clean
>
> # LBS is 512
> cat /sys/block/md0/queue/logical_block_size
>
> # create partition md0p1
> parted -s /dev/md0 mklabel gpt mkpart primary 1MiB 100%
> lsblk | grep md0p1
>
> # LBS becomes 4096 after adding sdf
> mdadm --add -q /dev/md0 /dev/sdf
> cat /sys/block/md0/queue/logical_block_size
>
> # partition lost
> partprobe /dev/md0
> lsblk | grep md0p1
> ```
>
> Simply restricting larger-LBS disks is inflexible. In some scenarios,
> only disks with 512 bytes LBS are available currently, but later, disks
> with 4KB LBS may be added to the array.
>
> Making LBS configurable is the best way to solve this scenario.
> After this patch, the raid will:
> - store LBS in disk metadata
> - add a read-write sysfs 'mdX/logical_block_size'
>
> Future mdadm should support setting LBS via metadata field during RAID
> creation and the new sysfs. Though the kernel allows runtime LBS changes,
> users should avoid modifying it after creating partitions or filesystems
> to prevent compatibility issues.
>
> Only 1.x metadata supports configurable LBS. 0.90 metadata inits all
> fields to default values at auto-detect. Supporting 0.90 would require
> more extensive changes and no such use case has been observed.
>
> Note that many RAID paths rely on PAGE_SIZE alignment, including for
> metadata I/O. A larger LBS than PAGE_SIZE will result in metadata
> read/write failures. So this config should be prevented.
>
> Signed-off-by: Li Nan <linan122@...wei.com>
> ---
> Documentation/admin-guide/md.rst | 10 +++++
> drivers/md/md.h | 1 +
> include/uapi/linux/raid/md_p.h | 3 +-
> drivers/md/md-linear.c | 1 +
> drivers/md/md.c | 77 ++++++++++++++++++++++++++++++++
> drivers/md/raid0.c | 1 +
> drivers/md/raid1.c | 1 +
> drivers/md/raid10.c | 1 +
> drivers/md/raid5.c | 1 +
> 9 files changed, 95 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/md.rst b/Documentation/admin-guide/md.rst
> index 1c2eacc94758..b7e7081889fe 100644
> --- a/Documentation/admin-guide/md.rst
> +++ b/Documentation/admin-guide/md.rst
> @@ -238,6 +238,16 @@ All md devices contain:
> the number of devices in a raid4/5/6, or to support external
> metadata formats which mandate such clipping.
>
> + logical_block_size
> + Configure the array's logical block size in bytes. This attribute
> + is only supported for 1.x meta. Write the value before starting
> + array. The final array LBS uses the maximum between this
> + configuration and LBS of all combined devices. Note that
> + LBS cannot exceed PAGE_SIZE before RAID supports folio.
> + WARNING: Arrays created on new kernel cannot be assembled at old
> + kernel due to padding check, Set module parameter 'check_new_feature'
> + to false to bypass, but data loss may occur.
> +
> reshape_position
> This is either ``none`` or a sector number within the devices of
> the array where ``reshape`` is up to. If this is set, the three
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index 38a7c2fab150..a6b3cb69c28c 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -432,6 +432,7 @@ struct mddev {
> sector_t array_sectors; /* exported array size */
> int external_size; /* size managed
> * externally */
> + unsigned int logical_block_size;
> __u64 events;
> /* If the last 'event' was simply a clean->dirty transition, and
> * we didn't write it to the spares, then it is safe and simple
> diff --git a/include/uapi/linux/raid/md_p.h b/include/uapi/linux/raid/md_p.h
> index ac74133a4768..310068bb2a1d 100644
> --- a/include/uapi/linux/raid/md_p.h
> +++ b/include/uapi/linux/raid/md_p.h
> @@ -291,7 +291,8 @@ struct mdp_superblock_1 {
> __le64 resync_offset; /* data before this offset (from data_offset) known to be in sync */
> __le32 sb_csum; /* checksum up to devs[max_dev] */
> __le32 max_dev; /* size of devs[] array to consider */
> - __u8 pad3[64-32]; /* set to 0 when writing */
> + __le32 logical_block_size; /* same as q->limits->logical_block_size */
> + __u8 pad3[64-36]; /* set to 0 when writing */
>
> /* device state information. Indexed by dev_number.
> * 2 bytes per device
> diff --git a/drivers/md/md-linear.c b/drivers/md/md-linear.c
> index 7033d982d377..50d4a419a16e 100644
> --- a/drivers/md/md-linear.c
> +++ b/drivers/md/md-linear.c
> @@ -72,6 +72,7 @@ static int linear_set_limits(struct mddev *mddev)
>
> md_init_stacking_limits(&lim);
> lim.max_hw_sectors = mddev->chunk_sectors;
> + lim.logical_block_size = mddev->logical_block_size;
> lim.max_write_zeroes_sectors = mddev->chunk_sectors;
> lim.max_hw_wzeroes_unmap_sectors = mddev->chunk_sectors;
> lim.io_min = mddev->chunk_sectors << 9;
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 5921fb245bfa..e5f994c33dfe 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -1998,6 +1998,7 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *freshest, struc
> mddev->layout = le32_to_cpu(sb->layout);
> mddev->raid_disks = le32_to_cpu(sb->raid_disks);
> mddev->dev_sectors = le64_to_cpu(sb->size);
> + mddev->logical_block_size = le32_to_cpu(sb->logical_block_size);
> mddev->events = ev1;
> mddev->bitmap_info.offset = 0;
> mddev->bitmap_info.space = 0;
> @@ -2207,6 +2208,7 @@ static void super_1_sync(struct mddev *mddev, struct md_rdev *rdev)
> sb->chunksize = cpu_to_le32(mddev->chunk_sectors);
> sb->level = cpu_to_le32(mddev->level);
> sb->layout = cpu_to_le32(mddev->layout);
> + sb->logical_block_size = cpu_to_le32(mddev->logical_block_size);
> if (test_bit(FailFast, &rdev->flags))
> sb->devflags |= FailFast1;
> else
> @@ -5935,6 +5937,68 @@ static struct md_sysfs_entry md_serialize_policy =
> __ATTR(serialize_policy, S_IRUGO | S_IWUSR, serialize_policy_show,
> serialize_policy_store);
>
> +static int mddev_set_logical_block_size(struct mddev *mddev,
> + unsigned int lbs)
> +{
> + int err = 0;
> + struct queue_limits lim;
> +
> + if (queue_logical_block_size(mddev->gendisk->queue) >= lbs) {
> + pr_err("%s: Cannot set LBS smaller than mddev LBS %u\n",
> + mdname(mddev), lbs);
> + return -EINVAL;
> + }
> +
> + lim = queue_limits_start_update(mddev->gendisk->queue);
> + lim.logical_block_size = lbs;
> + pr_info("%s: logical_block_size is changed, data may be lost\n",
> + mdname(mddev));
> + err = queue_limits_commit_update(mddev->gendisk->queue, &lim);
> + if (err)
> + return err;
> +
> + mddev->logical_block_size = lbs;
> + /* New lbs will be written to superblock after array is running */
> + set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);
> + return 0;
> +}
> +
> +static ssize_t
> +lbs_show(struct mddev *mddev, char *page)
> +{
> + return sprintf(page, "%u\n", mddev->logical_block_size);
> +}
> +
> +static ssize_t
> +lbs_store(struct mddev *mddev, const char *buf, size_t len)
> +{
> + unsigned int lbs;
> + int err = -EBUSY;
> +
> + /* Only 1.x meta supports configurable LBS */
> + if (mddev->major_version == 0)
> + return -EINVAL;
> +
> + if (mddev->pers)
> + return -EBUSY;
> +
> + err = kstrtouint(buf, 10, &lbs);
> + if (err < 0)
> + return -EINVAL;
> +
> + err = mddev_lock(mddev);
> + if (err)
> + goto unlock;
> +
> + err = mddev_set_logical_block_size(mddev, lbs);
> +
> +unlock:
> + mddev_unlock(mddev);
> + return err ?: len;
> +}
> +
> +static struct md_sysfs_entry md_logical_block_size =
> +__ATTR(logical_block_size, 0644, lbs_show, lbs_store);
>
> static struct attribute *md_default_attrs[] = {
> &md_level.attr,
> @@ -5957,6 +6021,7 @@ static struct attribute *md_default_attrs[] = {
> &md_consistency_policy.attr,
> &md_fail_last_dev.attr,
> &md_serialize_policy.attr,
> + &md_logical_block_size.attr,
> NULL,
> };
>
> @@ -6087,6 +6152,17 @@ int mddev_stack_rdev_limits(struct mddev *mddev, struct queue_limits *lim,
> return -EINVAL;
> }
>
> + /*
> + * Before RAID adding folio support, the logical_block_size
> + * should be smaller than the page size.
> + */
> + if (lim->logical_block_size > PAGE_SIZE) {
> + pr_err("%s: logical_block_size must not larger than PAGE_SIZE\n",
> + mdname(mddev));
> + return -EINVAL;
> + }
> + mddev->logical_block_size = lim->logical_block_size;
> +
> return 0;
> }
> EXPORT_SYMBOL_GPL(mddev_stack_rdev_limits);
> @@ -6698,6 +6774,7 @@ static void md_clean(struct mddev *mddev)
> mddev->chunk_sectors = 0;
> mddev->ctime = mddev->utime = 0;
> mddev->layout = 0;
> + mddev->logical_block_size = 0;
> mddev->max_disks = 0;
> mddev->events = 0;
> mddev->can_decrease_events = 0;
> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index fbf763401521..47aee1b1d4d1 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -380,6 +380,7 @@ static int raid0_set_limits(struct mddev *mddev)
> lim.max_hw_sectors = mddev->chunk_sectors;
> lim.max_write_zeroes_sectors = mddev->chunk_sectors;
> lim.max_hw_wzeroes_unmap_sectors = mddev->chunk_sectors;
> + lim.logical_block_size = mddev->logical_block_size;
> lim.io_min = mddev->chunk_sectors << 9;
> lim.io_opt = lim.io_min * mddev->raid_disks;
> lim.chunk_sectors = mddev->chunk_sectors;
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 64bfe8ca5b38..167768edaec1 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -3212,6 +3212,7 @@ static int raid1_set_limits(struct mddev *mddev)
> md_init_stacking_limits(&lim);
> lim.max_write_zeroes_sectors = 0;
> lim.max_hw_wzeroes_unmap_sectors = 0;
> + lim.logical_block_size = mddev->logical_block_size;
> lim.features |= BLK_FEAT_ATOMIC_WRITES;
> err = mddev_stack_rdev_limits(mddev, &lim, MDDEV_STACK_INTEGRITY);
> if (err)
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 6b2d4b7057ae..71bfed3b798d 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -4000,6 +4000,7 @@ static int raid10_set_queue_limits(struct mddev *mddev)
> md_init_stacking_limits(&lim);
> lim.max_write_zeroes_sectors = 0;
> lim.max_hw_wzeroes_unmap_sectors = 0;
> + lim.logical_block_size = mddev->logical_block_size;
> lim.io_min = mddev->chunk_sectors << 9;
> lim.chunk_sectors = mddev->chunk_sectors;
> lim.io_opt = lim.io_min * raid10_nr_stripes(conf);
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index aa404abf5d17..92473850f381 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -7747,6 +7747,7 @@ static int raid5_set_limits(struct mddev *mddev)
> stripe = roundup_pow_of_two(data_disks * (mddev->chunk_sectors << 9));
>
> md_init_stacking_limits(&lim);
> + lim.logical_block_size = mddev->logical_block_size;
> lim.io_min = mddev->chunk_sectors << 9;
> lim.io_opt = lim.io_min * (conf->raid_disks - conf->max_degraded);
> lim.features |= BLK_FEAT_RAID_PARTIAL_STRIPES_EXPENSIVE;
> --
> 2.39.2
>
Looks good to me.
Reviewed-by: Xiao Ni <xni@...hat.com>
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