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

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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: Xiao Ni <xni@redhat.com>
Link: https://lore.kernel.org/linux-raid/20260323054644.3351791-4-yukuai@fnnas.com/
Signed-off-by: Yu Kuai <yukuai@fnnas.com>
This commit is contained in:
Yu Kuai
2026-03-23 13:46:44 +08:00
parent 4403023e2a
commit e92a5325b5
1 changed files with 61 additions and 1 deletions
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62
drivers/md/md-llbitmap.c
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@@ -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);