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-rw-r--r--fs/btrfs/scrub.c21
1 files changed, 20 insertions, 1 deletions
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index e2c87220600f..bd3f2266c5f4 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3559,7 +3559,26 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
* -> btrfs_scrub_pause()
*/
scrub_pause_on(fs_info);
- ret = btrfs_inc_block_group_ro(cache);
+
+ /*
+ * Don't do chunk preallocation for scrub.
+ *
+ * This is especially important for SYSTEM bgs, or we can hit
+ * -EFBIG from btrfs_finish_chunk_alloc() like:
+ * 1. The only SYSTEM bg is marked RO.
+ * Since SYSTEM bg is small, that's pretty common.
+ * 2. New SYSTEM bg will be allocated
+ * Due to regular version will allocate new chunk.
+ * 3. New SYSTEM bg is empty and will get cleaned up
+ * Before cleanup really happens, it's marked RO again.
+ * 4. Empty SYSTEM bg get scrubbed
+ * We go back to 2.
+ *
+ * This can easily boost the amount of SYSTEM chunks if cleaner
+ * thread can't be triggered fast enough, and use up all space
+ * of btrfs_super_block::sys_chunk_array
+ */
+ ret = btrfs_inc_block_group_ro(cache, false);
if (!ret && sctx->is_dev_replace) {
/*
* If we are doing a device replace wait for any tasks