Commit e92a5325 authored by Yu Kuai's avatar Yu Kuai
Browse files

md/md-llbitmap: optimize initial sync with write_zeroes_unmap support 



For RAID-456 arrays with llbitmap, if all underlying disks support
write_zeroes with unmap, issue write_zeroes to zero all disk data
regions and initialize the bitmap to BitCleanUnwritten instead of
BitUnwritten.

This optimization skips the initial XOR parity building because:
1. write_zeroes with unmap guarantees zeroed reads after the operation
2. For RAID-456, when all data is zero, parity is automatically
   consistent (0 XOR 0 XOR ... = 0)
3. BitCleanUnwritten indicates parity is valid but no user data
   has been written

The implementation adds two helper functions:
- llbitmap_all_disks_support_wzeroes_unmap(): Checks if all active
  disks support write_zeroes with unmap
- llbitmap_zero_all_disks(): Issues blkdev_issue_zeroout() to each
  rdev's data region to zero all disks

The zeroing and bitmap state setting happens in llbitmap_init_state()
during bitmap initialization. If any disk fails to zero, we fall back
to BitUnwritten and normal lazy recovery.

This significantly reduces array initialization time for RAID-456
arrays built on modern NVMe SSDs or other devices that support
write_zeroes with unmap.

Reviewed-by: default avatarXiao Ni <xni@redhat.com>
Link: https://lore.kernel.org/linux-raid/20260323054644.3351791-4-yukuai@fnnas.com/


Signed-off-by: default avatarYu Kuai <yukuai@fnnas.com>
parent 4403023e

drivers/md/md-llbitmap.c

+61 −1
Original line number Diff line number Diff line
@@ -654,13 +654,73 @@ static int llbitmap_cache_pages(struct llbitmap *llbitmap) 
	return 0;

}



/*

 * Check if all underlying disks support write_zeroes with unmap.

 */

static bool llbitmap_all_disks_support_wzeroes_unmap(struct llbitmap *llbitmap)

{

	struct mddev *mddev = llbitmap->mddev;

	struct md_rdev *rdev;



	rdev_for_each(rdev, mddev) {

		if (rdev->raid_disk < 0 || test_bit(Faulty, &rdev->flags))

			continue;



		if (bdev_write_zeroes_unmap_sectors(rdev->bdev) == 0)

			return false;

	}



	return true;

}



/*

 * Issue write_zeroes to all underlying disks to zero their data regions.

 * This ensures parity consistency for RAID-456 (0 XOR 0 = 0).

 * Returns true if all disks were successfully zeroed.

 */

static bool llbitmap_zero_all_disks(struct llbitmap *llbitmap)

{

	struct mddev *mddev = llbitmap->mddev;

	struct md_rdev *rdev;

	sector_t dev_sectors = mddev->dev_sectors;

	int ret;



	rdev_for_each(rdev, mddev) {

		if (rdev->raid_disk < 0 || test_bit(Faulty, &rdev->flags))

			continue;



		ret = blkdev_issue_zeroout(rdev->bdev,

					   rdev->data_offset,

					   dev_sectors,

					   GFP_KERNEL, 0);

		if (ret) {

			pr_warn("md/llbitmap: failed to zero disk %pg: %d\n",

				rdev->bdev, ret);

			return false;

		}

	}



	return true;

}



static void llbitmap_init_state(struct llbitmap *llbitmap)

{

	struct mddev *mddev = llbitmap->mddev;

	enum llbitmap_state state = BitUnwritten;

	unsigned long i;



	if (test_and_clear_bit(BITMAP_CLEAN, &llbitmap->flags))

	if (test_and_clear_bit(BITMAP_CLEAN, &llbitmap->flags)) {

		state = BitClean;

	} else if (raid_is_456(mddev) &&

		   llbitmap_all_disks_support_wzeroes_unmap(llbitmap)) {

		/*

		 * All disks support write_zeroes with unmap. Zero all disks

		 * to ensure parity consistency, then set BitCleanUnwritten

		 * to skip initial sync.

		 */

		if (llbitmap_zero_all_disks(llbitmap))

			state = BitCleanUnwritten;

	}



	for (i = 0; i < llbitmap->chunks; i++)

		llbitmap_write(llbitmap, state, i);