Re: [PATCH] md/md-llbitmap: track bitmap sync_size explicitly

[Su Yue <l@damenly.org>]

On Fri 05 Jun 2026 at 17:15, Yu Kuai <yukuai@kernel.org> wrote:

> From: Yu Kuai <yukuai@fygo.io>
>
> Track llbitmap's own sync_size instead of always using
> mddev->resync_max_sectors directly.
>
> This is the minimal bookkeeping needed before llbitmap can track 
> old
> and new reshape geometry independently.
>
> Signed-off-by: Yu Kuai <yukuai@fygo.io>
>
Reviewed-by: Su Yue <glass.su@suse.com>
> ---
>  drivers/md/md-llbitmap.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/md-llbitmap.c b/drivers/md/md-llbitmap.c
> index bcf34f0c9af6..ecf3ed712315 100644
> --- a/drivers/md/md-llbitmap.c
> +++ b/drivers/md/md-llbitmap.c
> @@ -285,10 +285,12 @@ struct llbitmap {
>  	unsigned long chunkshift;
>  	/* size of one chunk in sector */
>  	unsigned long chunksize;
>  	/* total number of chunks */
>  	unsigned long chunks;
> +	/* total number of sectors tracked by current bitmap geometry 
> */
> +	sector_t sync_size;
>  	unsigned long last_end_sync;
>  	/*
>  	 * time in seconds that dirty bits will be cleared if the page 
>  is not
>  	 * accessed.
>  	 */
> @@ -916,10 +918,11 @@ static int llbitmap_init(struct llbitmap 
> *llbitmap)
>
>  	llbitmap->barrier_idle = DEFAULT_BARRIER_IDLE;
>  	llbitmap->chunkshift = ffz(~chunksize);
>  	llbitmap->chunksize = chunksize;
>  	llbitmap->chunks = chunks;
> +	llbitmap->sync_size = blocks;
>  	mddev->bitmap_info.daemon_sleep = DEFAULT_DAEMON_SLEEP;
>
>  	ret = llbitmap_cache_pages(llbitmap);
>  	if (ret)
>  		return ret;
> @@ -936,10 +939,11 @@ static int llbitmap_read_sb(struct 
> llbitmap *llbitmap)
>  {
>  	struct mddev *mddev = llbitmap->mddev;
>  	unsigned long daemon_sleep;
>  	unsigned long chunksize;
>  	unsigned long events;
> +	sector_t sync_size;
>  	struct page *sb_page;
>  	bitmap_super_t *sb;
>  	int ret = -EINVAL;
>
>  	if (!mddev->bitmap_info.offset) {
> @@ -985,10 +989,13 @@ static int llbitmap_read_sb(struct 
> llbitmap *llbitmap)
>  	if (test_and_clear_bit(BITMAP_FIRST_USE, &llbitmap->flags)) {
>  		ret = llbitmap_init(llbitmap);
>  		goto out_put_page;
>  	}
>
> +	sync_size = le64_to_cpu(sb->sync_size);
> +	if (!sync_size)
> +		sync_size = mddev->resync_max_sectors;
>  	chunksize = le32_to_cpu(sb->chunksize);
>  	if (!is_power_of_2(chunksize)) {
>  		pr_err("md/llbitmap: %s: chunksize not a power of 2",
>  		       mdname(mddev));
>  		goto out_put_page;
> @@ -1020,12 +1027,13 @@ static int llbitmap_read_sb(struct 
> llbitmap *llbitmap)
>  	mddev->bitmap_info.chunksize = chunksize;
>  	mddev->bitmap_info.daemon_sleep = daemon_sleep;
>
>  	llbitmap->barrier_idle = DEFAULT_BARRIER_IDLE;
>  	llbitmap->chunksize = chunksize;
> -	llbitmap->chunks = 
> DIV_ROUND_UP_SECTOR_T(mddev->resync_max_sectors, chunksize);
> +	llbitmap->chunks = DIV_ROUND_UP_SECTOR_T(sync_size, 
> chunksize);
>  	llbitmap->chunkshift = ffz(~chunksize);
> +	llbitmap->sync_size = sync_size;
>  	ret = llbitmap_cache_pages(llbitmap);
>
>  out_put_page:
>  	__free_page(sb_page);
>  	kunmap_local(sb);
> @@ -1151,10 +1159,11 @@ static int llbitmap_resize(struct mddev 
> *mddev, sector_t blocks, int chunksize)
>  	}
>
>  	llbitmap->chunkshift = ffz(~chunksize);
>  	llbitmap->chunksize = chunksize;
>  	llbitmap->chunks = chunks;
> +	llbitmap->sync_size = blocks;
>
>  	return 0;
>  }
>
>  static int llbitmap_load(struct mddev *mddev)
> @@ -1524,11 +1533,11 @@ static void llbitmap_update_sb(void 
> *data)
>
>  	sb = kmap_local_page(sb_page);
>  	sb->events = cpu_to_le64(mddev->events);
>  	sb->state = cpu_to_le32(llbitmap->flags);
>  	sb->chunksize = cpu_to_le32(llbitmap->chunksize);
> -	sb->sync_size = cpu_to_le64(mddev->resync_max_sectors);
> +	sb->sync_size = cpu_to_le64(llbitmap->sync_size);
>  	sb->events_cleared = cpu_to_le64(llbitmap->events_cleared);
>  	sb->sectors_reserved = cpu_to_le32(mddev->bitmap_info.space);
>  	sb->daemon_sleep = 
>  cpu_to_le32(mddev->bitmap_info.daemon_sleep);
>
>  	kunmap_local(sb);
> @@ -1542,10 +1551,11 @@ static int llbitmap_get_stats(void 
> *data, struct md_bitmap_stats *stats)
>  	memset(stats, 0, sizeof(*stats));
>
>  	stats->missing_pages = 0;
>  	stats->pages = llbitmap->nr_pages;
>  	stats->file_pages = llbitmap->nr_pages;
> +	stats->sync_size = llbitmap->sync_size;
>
>  	stats->behind_writes = atomic_read(&llbitmap->behind_writes);
>  	stats->behind_wait = wq_has_sleeper(&llbitmap->behind_wait);
>  	stats->events_cleared = llbitmap->events_cleared;