Btrfs has btrfs_end_transaction_throttle() which could try to commit transaction when needed.
However under most cases btrfs_end_transaction_throttle() won't really commit transaction, due to the hard timing requirement. Now introduce a new error injection point, btrfs_need_trans_pressure(), to allow btrfs_should_end_transaction() to return 1 and btrfs_end_transaction_throttle() to fallback to btrfs_commit_transaction(). With such more aggressive transaction commit, we can dig deeper into cases like snapshot drop. Now each reference drop of btrfs_drop_snapshot() will lead to a transaction commit, allowing dm-logwrites to catch more details, other than one big transaction dropping everything. Signed-off-by: Qu Wenruo <w...@suse.com> --- Changelog: v2: - Add comment to explain why this function is needed --- fs/btrfs/transaction.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 3f6811cdf803..8c5471b01d03 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -10,6 +10,7 @@ #include <linux/pagemap.h> #include <linux/blkdev.h> #include <linux/uuid.h> +#include <linux/error-injection.h> #include "ctree.h" #include "disk-io.h" #include "transaction.h" @@ -749,10 +750,25 @@ void btrfs_throttle(struct btrfs_fs_info *fs_info) wait_current_trans(fs_info); } +/* + * This function is to allow BPF to override the return value so that we can + * make btrfs to commit transaction more aggressively. + * + * It's a debug only feature, mainly used with dm-log-writes to catch more details + * of transient operations like balance and subvolume drop. + */ +static noinline bool btrfs_need_trans_pressure(struct btrfs_trans_handle *trans) +{ + return false; +} +ALLOW_ERROR_INJECTION(btrfs_need_trans_pressure, TRUE); + static int should_end_transaction(struct btrfs_trans_handle *trans) { struct btrfs_fs_info *fs_info = trans->fs_info; + if (btrfs_need_trans_pressure(trans)) + return 1; if (btrfs_check_space_for_delayed_refs(fs_info)) return 1; @@ -813,6 +829,8 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans, btrfs_trans_release_chunk_metadata(trans); + if (throttle && btrfs_need_trans_pressure(trans)) + return btrfs_commit_transaction(trans); if (lock && READ_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) { if (throttle) return btrfs_commit_transaction(trans); -- 2.22.0