From f7a6246bab1541d7208a5f0f9f0c6cac114e38da Mon Sep 17 00:00:00 2001 From: Zhao Heming Date: Wed, 3 Feb 2021 08:22:51 +0800 Subject: [PATCH 2/2] super1.c: avoid useless sync when bitmap switches from clustered to none With kernel commit 480523feae58 ("md: only call set_in_sync() when it is expected to succeed."), mddev->in_sync in clustered array is always zero. It makes metadata resync_offset to always zero. When assembling a clusterd array with "-U no-bitmap" option, kernel md layer "mddev->resync_offset == 0" and "mddev->bitmap == NULL" will trigger raid1 do sync on every bitmap chunk. the sync action is useless, we should avoid it. Related kernel flow: ``` md_do_sync mddev->pers->sync_request raid1_sync_request md_bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) __bitmap_start_sync(bitmap, offset,&blocks1, degraded) if (bitmap == NULL) {/* FIXME or bitmap set as 'failed' */ *blocks = 1024; return 1; /* always resync if no bitmap */ } ``` Reprodusible steps: ``` node1 # mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sd{a,b} node1 # mdadm -Ss (in another shell, executing & watching: watch -n 1 'cat /proc/mdstat') node1 # mdadm -A -U no-bitmap /dev/md0 /dev/sd{a,b} ``` Signed-off-by: Zhao Heming Signed-off-by: Jes Sorensen --- super1.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/super1.c b/super1.c index 70aa1d3d0219..7b03329dac91 100644 --- a/super1.c +++ b/super1.c @@ -1346,6 +1346,8 @@ static int update_super1(struct supertype *st, struct mdinfo *info, memcpy(bms->uuid, sb->set_uuid, 16); } else if (strcmp(update, "no-bitmap") == 0) { sb->feature_map &= ~__cpu_to_le32(MD_FEATURE_BITMAP_OFFSET); + if (bms->version == BITMAP_MAJOR_CLUSTERED && !IsBitmapDirty(devname)) + sb->resync_offset = MaxSector; } else if (strcmp(update, "bbl") == 0) { /* only possible if there is room after the bitmap, or if * there is no bitmap -- 1.8.3.1