Re: [PATCH v2 4/5] md/md-llbitmap: add CleanUnwritten state for RAID-5 proactive parity building

[Yu Kuai]

Hi,

在 2026/3/13 11:16, Xiao Ni 写道:
> On Mon, Feb 23, 2026 at 10:44 AM Yu Kuai <yukuai@xxxxxxxxx> wrote:
>> Add new states to the llbitmap state machine to support proactive XOR
>> parity building for RAID-5 arrays. This allows users to pre-build parity
>> data for unwritten regions before any user data is written.
>>
>> New states added:
>> - BitNeedSyncUnwritten: Transitional state when proactive sync is triggered
>>    via sysfs on Unwritten regions.
>> - BitSyncingUnwritten: Proactive sync in progress for unwritten region.
>> - BitCleanUnwritten: XOR parity has been pre-built, but no user data
>>    written yet. When user writes to this region, it transitions to BitDirty.
>>
>> New actions added:
>> - BitmapActionProactiveSync: Trigger for proactive XOR parity building.
>> - BitmapActionClearUnwritten: Convert CleanUnwritten/NeedSyncUnwritten/
>>    SyncingUnwritten states back to Unwritten before recovery starts.
>>
>> State flows:
>> - Current (lazy): Unwritten -> (write) -> NeedSync -> (sync) -> Dirty -> Clean
>> - New (proactive): Unwritten -> (sysfs) -> NeedSyncUnwritten -> (sync) -> CleanUnwritten
>> - On write to CleanUnwritten: CleanUnwritten -> (write) -> Dirty -> Clean
>> - On disk replacement: CleanUnwritten regions are converted to Unwritten
>>    before recovery starts, so recovery only rebuilds regions with user data
>>
>> A new sysfs interface is added at /sys/block/mdX/md/llbitmap/proactive_sync
>> (write-only) to trigger proactive sync. This only works for RAID-456 arrays.
>>
>> Signed-off-by: Yu Kuai <yukuai@xxxxxxxxx>
>> ---
>>   drivers/md/md-llbitmap.c | 140 +++++++++++++++++++++++++++++++++++----
>>   drivers/md/md.c          |   6 +-
>>   2 files changed, 132 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/md/md-llbitmap.c b/drivers/md/md-llbitmap.c
>> index 5f9e7004e3e3..461050b2771b 100644
>> --- a/drivers/md/md-llbitmap.c
>> +++ b/drivers/md/md-llbitmap.c
>> @@ -208,6 +208,20 @@ enum llbitmap_state {
>>          BitNeedSync,
>>          /* data is synchronizing */
>>          BitSyncing,
>> +       /*
>> +        * Proactive sync requested for unwritten region (raid456 only).
>> +        * Triggered via sysfs when user wants to pre-build XOR parity
>> +        * for regions that have never been written.
>> +        */
>> +       BitNeedSyncUnwritten,
>> +       /* Proactive sync in progress for unwritten region */
>> +       BitSyncingUnwritten,
>> +       /*
>> +        * XOR parity has been pre-built for a region that has never had
>> +        * user data written. When user writes to this region, it transitions
>> +        * to BitDirty.
>> +        */
>> +       BitCleanUnwritten,
>>          BitStateCount,
>>          BitNone = 0xff,
>>   };
>> @@ -232,6 +246,12 @@ enum llbitmap_action {
>>           * BitNeedSync.
>>           */
>>          BitmapActionStale,
>> +       /*
>> +        * Proactive sync trigger for raid456 - builds XOR parity for
>> +        * Unwritten regions without requiring user data write first.
>> +        */
>> +       BitmapActionProactiveSync,
>> +       BitmapActionClearUnwritten,
>>          BitmapActionCount,
>>          /* Init state is BitUnwritten */
>>          BitmapActionInit,
>> @@ -304,6 +324,8 @@ static char state_machine[BitStateCount][BitmapActionCount] = {
>>                  [BitmapActionDaemon]            = BitNone,
>>                  [BitmapActionDiscard]           = BitNone,
>>                  [BitmapActionStale]             = BitNone,
>> +               [BitmapActionProactiveSync]     = BitNeedSyncUnwritten,
>> +               [BitmapActionClearUnwritten]    = BitNone,
>>          },
>>          [BitClean] = {
>>                  [BitmapActionStartwrite]        = BitDirty,
>> @@ -314,6 +336,8 @@ static char state_machine[BitStateCount][BitmapActionCount] = {
>>                  [BitmapActionDaemon]            = BitNone,
>>                  [BitmapActionDiscard]           = BitUnwritten,
>>                  [BitmapActionStale]             = BitNeedSync,
>> +               [BitmapActionProactiveSync]     = BitNone,
>> +               [BitmapActionClearUnwritten]    = BitNone,
>>          },
>>          [BitDirty] = {
>>                  [BitmapActionStartwrite]        = BitNone,
>> @@ -324,6 +348,8 @@ static char state_machine[BitStateCount][BitmapActionCount] = {
>>                  [BitmapActionDaemon]            = BitClean,
>>                  [BitmapActionDiscard]           = BitUnwritten,
>>                  [BitmapActionStale]             = BitNeedSync,
>> +               [BitmapActionProactiveSync]     = BitNone,
>> +               [BitmapActionClearUnwritten]    = BitNone,
>>          },
>>          [BitNeedSync] = {
>>                  [BitmapActionStartwrite]        = BitNone,
>> @@ -334,6 +360,8 @@ static char state_machine[BitStateCount][BitmapActionCount] = {
>>                  [BitmapActionDaemon]            = BitNone,
>>                  [BitmapActionDiscard]           = BitUnwritten,
>>                  [BitmapActionStale]             = BitNone,
>> +               [BitmapActionProactiveSync]     = BitNone,
>> +               [BitmapActionClearUnwritten]    = BitNone,
>>          },
>>          [BitSyncing] = {
>>                  [BitmapActionStartwrite]        = BitNone,
>> @@ -344,6 +372,44 @@ static char state_machine[BitStateCount][BitmapActionCount] = {
>>                  [BitmapActionDaemon]            = BitNone,
>>                  [BitmapActionDiscard]           = BitUnwritten,
>>                  [BitmapActionStale]             = BitNeedSync,
>> +               [BitmapActionProactiveSync]     = BitNone,
>> +               [BitmapActionClearUnwritten]    = BitNone,
>> +       },
>> +       [BitNeedSyncUnwritten] = {
>> +               [BitmapActionStartwrite]        = BitNeedSync,
>> +               [BitmapActionStartsync]         = BitSyncingUnwritten,
>> +               [BitmapActionEndsync]           = BitNone,
>> +               [BitmapActionAbortsync]         = BitUnwritten,
>> +               [BitmapActionReload]            = BitUnwritten,
>> +               [BitmapActionDaemon]            = BitNone,
>> +               [BitmapActionDiscard]           = BitUnwritten,
>> +               [BitmapActionStale]             = BitUnwritten,
>> +               [BitmapActionProactiveSync]     = BitNone,
>> +               [BitmapActionClearUnwritten]    = BitUnwritten,
>> +       },
>> +       [BitSyncingUnwritten] = {
>> +               [BitmapActionStartwrite]        = BitSyncing,
>> +               [BitmapActionStartsync]         = BitSyncingUnwritten,
> Hi Kuai
>
> Is it ok to set the above state to BitNone? The orignal state is
> already BitSyncingUnwritten.
>
>> +               [BitmapActionEndsync]           = BitCleanUnwritten,
>> +               [BitmapActionAbortsync]         = BitUnwritten,
>> +               [BitmapActionReload]            = BitUnwritten,
>> +               [BitmapActionDaemon]            = BitNone,
>> +               [BitmapActionDiscard]           = BitUnwritten,
>> +               [BitmapActionStale]             = BitUnwritten,
>> +               [BitmapActionProactiveSync]     = BitNone,
>> +               [BitmapActionClearUnwritten]    = BitUnwritten,
>> +       },
>> +       [BitCleanUnwritten] = {
>> +               [BitmapActionStartwrite]        = BitDirty,
>> +               [BitmapActionStartsync]         = BitNone,
>> +               [BitmapActionEndsync]           = BitNone,
>> +               [BitmapActionAbortsync]         = BitNone,
>> +               [BitmapActionReload]            = BitNone,
>> +               [BitmapActionDaemon]            = BitNone,
>> +               [BitmapActionDiscard]           = BitUnwritten,
>> +               [BitmapActionStale]             = BitUnwritten,
>> +               [BitmapActionProactiveSync]     = BitNone,
>> +               [BitmapActionClearUnwritten]    = BitUnwritten,
>>          },
>>   };
>>
>> @@ -376,6 +442,7 @@ static void llbitmap_infect_dirty_bits(struct llbitmap *llbitmap,
>>                          pctl->state[pos] = level_456 ? BitNeedSync : BitDirty;
>>                          break;
>>                  case BitClean:
>> +               case BitCleanUnwritten:
>>                          pctl->state[pos] = BitDirty;
>>                          break;
>>                  }
>> @@ -383,7 +450,7 @@ static void llbitmap_infect_dirty_bits(struct llbitmap *llbitmap,
>>   }
>>
>>   static void llbitmap_set_page_dirty(struct llbitmap *llbitmap, int idx,
>> -                                   int offset)
>> +                                   int offset, bool infect)
>>   {
>>          struct llbitmap_page_ctl *pctl = llbitmap->pctl[idx];
>>          unsigned int io_size = llbitmap->io_size;
>> @@ -398,7 +465,7 @@ static void llbitmap_set_page_dirty(struct llbitmap *llbitmap, int idx,
>>           * resync all the dirty bits, hence skip infect new dirty bits to
>>           * prevent resync unnecessary data.
>>           */
>> -       if (llbitmap->mddev->degraded) {
>> +       if (llbitmap->mddev->degraded || !infect) {
>>                  set_bit(block, pctl->dirty);
>>                  return;
>>          }
>> @@ -438,7 +505,9 @@ static void llbitmap_write(struct llbitmap *llbitmap, enum llbitmap_state state,
>>
>>          llbitmap->pctl[idx]->state[bit] = state;
>>          if (state == BitDirty || state == BitNeedSync)
>> -               llbitmap_set_page_dirty(llbitmap, idx, bit);
>> +               llbitmap_set_page_dirty(llbitmap, idx, bit, true);
>> +       else if (state == BitNeedSyncUnwritten)
>> +               llbitmap_set_page_dirty(llbitmap, idx, bit, false);
>>   }
>>
>>   static struct page *llbitmap_read_page(struct llbitmap *llbitmap, int idx)
>> @@ -627,11 +696,10 @@ static enum llbitmap_state llbitmap_state_machine(struct llbitmap *llbitmap,
>>                          goto write_bitmap;
>>                  }
>>
>> -               if (c == BitNeedSync)
>> +               if (c == BitNeedSync || c == BitNeedSyncUnwritten)
>>                          need_resync = !mddev->degraded;
>>
>>                  state = state_machine[c][action];
>> -
>>   write_bitmap:
>>                  if (unlikely(mddev->degraded)) {
>>                          /* For degraded array, mark new data as need sync. */
>> @@ -658,8 +726,7 @@ static enum llbitmap_state llbitmap_state_machine(struct llbitmap *llbitmap,
>>                  }
>>
>>                  llbitmap_write(llbitmap, state, start);
>> -
>> -               if (state == BitNeedSync)
>> +               if (state == BitNeedSync || state == BitNeedSyncUnwritten)
>>                          need_resync = !mddev->degraded;
>>                  else if (state == BitDirty &&
>>                           !timer_pending(&llbitmap->pending_timer))
>> @@ -1229,7 +1296,7 @@ static bool llbitmap_blocks_synced(struct mddev *mddev, sector_t offset)
>>          unsigned long p = offset >> llbitmap->chunkshift;
>>          enum llbitmap_state c = llbitmap_read(llbitmap, p);
>>
>> -       return c == BitClean || c == BitDirty;
>> +       return c == BitClean || c == BitDirty || c == BitCleanUnwritten;
>>   }
>>
>>   static sector_t llbitmap_skip_sync_blocks(struct mddev *mddev, sector_t offset)
>> @@ -1243,6 +1310,10 @@ static sector_t llbitmap_skip_sync_blocks(struct mddev *mddev, sector_t offset)
>>          if (c == BitUnwritten)
>>                  return blocks;
>>
>> +       /* Skip CleanUnwritten - no user data, will be reset after recovery */
>> +       if (c == BitCleanUnwritten)
>> +               return blocks;
>> +
>>          /* For degraded array, don't skip */
>>          if (mddev->degraded)
>>                  return 0;
>> @@ -1261,14 +1332,25 @@ static bool llbitmap_start_sync(struct mddev *mddev, sector_t offset,
>>   {
>>          struct llbitmap *llbitmap = mddev->bitmap;
>>          unsigned long p = offset >> llbitmap->chunkshift;
>> +       enum llbitmap_state state;
>> +
>> +       /*
>> +        * Before recovery starts, convert CleanUnwritten to Unwritten.
>> +        * This ensures the new disk won't have stale parity data.
>> +        */
>> +       if (offset == 0 && test_bit(MD_RECOVERY_RECOVER, &mddev->recovery) &&
>> +           !test_bit(MD_RECOVERY_LAZY_RECOVER, &mddev->recovery))
>> +               llbitmap_state_machine(llbitmap, 0, llbitmap->chunks - 1,
>> +                                      BitmapActionClearUnwritten);
>> +
>>
>>          /*
>>           * Handle one bit at a time, this is much simpler. And it doesn't matter
>>           * if md_do_sync() loop more times.
>>           */
>>          *blocks = llbitmap->chunksize - (offset & (llbitmap->chunksize - 1));
>> -       return llbitmap_state_machine(llbitmap, p, p,
>> -                                     BitmapActionStartsync) == BitSyncing;
>> +       state = llbitmap_state_machine(llbitmap, p, p, BitmapActionStartsync);
>> +       return state == BitSyncing || state == BitSyncingUnwritten;
>>   }
>>
>>   /* Something is wrong, sync_thread stop at @offset */
>> @@ -1474,9 +1556,15 @@ static ssize_t bits_show(struct mddev *mddev, char *page)
>>          }
>>
>>          mutex_unlock(&mddev->bitmap_info.mutex);
>> -       return sprintf(page, "unwritten %d\nclean %d\ndirty %d\nneed sync %d\nsyncing %d\n",
>> +       return sprintf(page,
>> +                      "unwritten %d\nclean %d\ndirty %d\n"
>> +                      "need sync %d\nsyncing %d\n"
>> +                      "need sync unwritten %d\nsyncing unwritten %d\n"
>> +                      "clean unwritten %d\n",
>>                         bits[BitUnwritten], bits[BitClean], bits[BitDirty],
>> -                      bits[BitNeedSync], bits[BitSyncing]);
>> +                      bits[BitNeedSync], bits[BitSyncing],
>> +                      bits[BitNeedSyncUnwritten], bits[BitSyncingUnwritten],
>> +                      bits[BitCleanUnwritten]);
>>   }
>>
>>   static struct md_sysfs_entry llbitmap_bits = __ATTR_RO(bits);
>> @@ -1549,11 +1637,39 @@ barrier_idle_store(struct mddev *mddev, const char *buf, size_t len)
>>
>>   static struct md_sysfs_entry llbitmap_barrier_idle = __ATTR_RW(barrier_idle);
>>
>> +static ssize_t
>> +proactive_sync_store(struct mddev *mddev, const char *buf, size_t len)
>> +{
>> +       struct llbitmap *llbitmap;
>> +
>> +       /* Only for RAID-456 */
>> +       if (!raid_is_456(mddev))
>> +               return -EINVAL;
>> +
>> +       mutex_lock(&mddev->bitmap_info.mutex);
>> +       llbitmap = mddev->bitmap;
>> +       if (!llbitmap || !llbitmap->pctl) {
>> +               mutex_unlock(&mddev->bitmap_info.mutex);
>> +               return -ENODEV;
>> +       }
>> +
>> +       /* Trigger proactive sync on all Unwritten regions */
>> +       llbitmap_state_machine(llbitmap, 0, llbitmap->chunks - 1,
>> +                              BitmapActionProactiveSync);
>> +
>> +       mutex_unlock(&mddev->bitmap_info.mutex);
>> +       return len;
>> +}
>> +
>> +static struct md_sysfs_entry llbitmap_proactive_sync =
>> +       __ATTR(proactive_sync, 0200, NULL, proactive_sync_store);
>> +
>>   static struct attribute *md_llbitmap_attrs[] = {
>>          &llbitmap_bits.attr,
>>          &llbitmap_metadata.attr,
>>          &llbitmap_daemon_sleep.attr,
>>          &llbitmap_barrier_idle.attr,
>> +       &llbitmap_proactive_sync.attr,
>>          NULL
>>   };
>>
>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>> index 245785ad0ffd..b6543d81ac96 100644
>> --- a/drivers/md/md.c
>> +++ b/drivers/md/md.c
>> @@ -9878,8 +9878,10 @@ void md_do_sync(struct md_thread *thread)
>>                                   * Give other IO more of a chance.
>>                                   * The faster the devices, the less we wait.
>>                                   */
>> -                               wait_event(mddev->recovery_wait,
>> -                                          !atomic_read(&mddev->recovery_active));
>> +                               wait_event_timeout(
>> +                                       mddev->recovery_wait,
>> +                                       !atomic_read(&mddev->recovery_active),
>> +                                       HZ);
> Could you explain this change? It no longer waits for synchronous I/O
> to finish when the sync speed is fast. Does it have relasionship with
> this major change of this patch?

I should separate this change into another patch, I didn't notice this was
amended into this patch.

And I'll also check the return value and goto repeat if timeout, instead of
waiting for all sync_io to be done, I think this is more graceful and can allow
sync io to be issued once current speed is less than sync speed min.

>
> Best Regards
> Xiao
>>                          }
>>                  }
>>          }
>> --
>> 2.51.0
>>
>>
-- 
Thansk,
Kuai