jbd2: remove journal_clean_one_cp_list()

journal_clean_one_cp_list() and journal_shrink_one_cp_list() are almost
the same, so merge them into journal_shrink_one_cp_list(), remove the
nr_to_scan parameter, always scan and try to free the whole checkpoint
list.

Signed-off-by: Zhang Yi <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Theodore Ts'o <[e-mail]>

fs/jbd2/checkpoint.c

···
 /* Checkpoint list management */
 
 /*
- * journal_clean_one_cp_list
+ * journal_shrink_one_cp_list
  *
- * Find all the written-back checkpoint buffers in the given list and
- * release them. If 'destroy' is set, clean all buffers unconditionally.
+ * Find all the written-back checkpoint buffers in the given list
+ * and try to release them. If the whole transaction is released, set
+ * the 'released' parameter. Return the number of released checkpointed
+ * buffers.
  *
  * Called with j_list_lock held.
- * Returns 1 if we freed the transaction, 0 otherwise.
  */
-static int journal_clean_one_cp_list(struct journal_head *jh, bool destroy)
+static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
+						bool destroy, bool *released)
 {
 	struct journal_head *last_jh;
 	struct journal_head *next_jh = jh;
+	unsigned long nr_freed = 0;
+	int ret;
 
+	*released = false;
 	if (!jh)
 		return 0;
 
···
 		next_jh = jh->b_cpnext;
 
 		if (!destroy && __cp_buffer_busy(jh))
-			return 0;
-
-		if (__jbd2_journal_remove_checkpoint(jh))
-			return 1;
-		/*
-		 * This function only frees up some memory
-		 * if possible so we dont have an obligation
-		 * to finish processing. Bail out if preemption
-		 * requested:
-		 */
-		if (need_resched())
-			return 0;
-	} while (jh != last_jh);
-
-	return 0;
-}
-
-/*
- * journal_shrink_one_cp_list
- *
- * Find 'nr_to_scan' written-back checkpoint buffers in the given list
- * and try to release them. If the whole transaction is released, set
- * the 'released' parameter. Return the number of released checkpointed
- * buffers.
- *
- * Called with j_list_lock held.
- */
-static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
-						unsigned long *nr_to_scan,
-						bool *released)
-{
-	struct journal_head *last_jh;
-	struct journal_head *next_jh = jh;
-	unsigned long nr_freed = 0;
-	int ret;
-
-	if (!jh || *nr_to_scan == 0)
-		return 0;
-
-	last_jh = jh->b_cpprev;
-	do {
-		jh = next_jh;
-		next_jh = jh->b_cpnext;
-
-		(*nr_to_scan)--;
-		if (__cp_buffer_busy(jh))
 			continue;
 
 		nr_freed++;
···
 
 		if (need_resched())
 			break;
-	} while (jh != last_jh && *nr_to_scan);
+	} while (jh != last_jh);
 
 	return nr_freed;
 }
···
 						  unsigned long *nr_to_scan)
 {
 	transaction_t *transaction, *last_transaction, *next_transaction;
-	bool released;
+	bool __maybe_unused released;
 	tid_t first_tid = 0, last_tid = 0, next_tid = 0;
 	tid_t tid = 0;
 	unsigned long nr_freed = 0;
-	unsigned long nr_scanned = *nr_to_scan;
+	unsigned long freed;
 
 again:
 	spin_lock(&journal->j_list_lock);
···
 		transaction = next_transaction;
 		next_transaction = transaction->t_cpnext;
 		tid = transaction->t_tid;
-		released = false;
 
-		nr_freed += journal_shrink_one_cp_list(transaction->t_checkpoint_list,
-						       nr_to_scan, &released);
+		freed = journal_shrink_one_cp_list(transaction->t_checkpoint_list,
+						   false, &released);
+		nr_freed += freed;
+		(*nr_to_scan) -= min(*nr_to_scan, freed);
 		if (*nr_to_scan == 0)
 			break;
 		if (need_resched() || spin_needbreak(&journal->j_list_lock))
···
 	if (*nr_to_scan && next_tid)
 		goto again;
 out:
-	nr_scanned -= *nr_to_scan;
 	trace_jbd2_shrink_checkpoint_list(journal, first_tid, tid, last_tid,
-					  nr_freed, nr_scanned, next_tid);
+					  nr_freed, next_tid);
 
 	return nr_freed;
 }
···
 void __jbd2_journal_clean_checkpoint_list(journal_t *journal, bool destroy)
 {
 	transaction_t *transaction, *last_transaction, *next_transaction;
-	int ret;
+	bool released;
 
 	transaction = journal->j_checkpoint_transactions;
 	if (!transaction)
···
 	do {
 		transaction = next_transaction;
 		next_transaction = transaction->t_cpnext;
-		ret = journal_clean_one_cp_list(transaction->t_checkpoint_list,
-						destroy);
+		journal_shrink_one_cp_list(transaction->t_checkpoint_list,
+					   destroy, &released);
 		/*
 		 * This function only frees up some memory if possible so we
 		 * dont have an obligation to finish processing. Bail out if
···
 		 * avoids pointless scanning of transactions which still
 		 * weren't checkpointed.
 		 */
-		if (!ret)
+		if (!released)
 			return;
 	} while (transaction != last_transaction);
 }

include/trace/events/jbd2.h

···
 TRACE_EVENT(jbd2_shrink_checkpoint_list,
 
 	TP_PROTO(journal_t *journal, tid_t first_tid, tid_t tid, tid_t last_tid,
-		 unsigned long nr_freed, unsigned long nr_scanned,
-		 tid_t next_tid),
+		 unsigned long nr_freed, tid_t next_tid),
 
-	TP_ARGS(journal, first_tid, tid, last_tid, nr_freed,
-		nr_scanned, next_tid),
+	TP_ARGS(journal, first_tid, tid, last_tid, nr_freed, next_tid),
 
 	TP_STRUCT__entry(
 		__field(dev_t, dev)
···
 		__field(tid_t, tid)
 		__field(tid_t, last_tid)
 		__field(unsigned long, nr_freed)
-		__field(unsigned long, nr_scanned)
 		__field(tid_t, next_tid)
 	),
 
···
 		__entry->tid		= tid;
 		__entry->last_tid	= last_tid;
 		__entry->nr_freed	= nr_freed;
-		__entry->nr_scanned	= nr_scanned;
 		__entry->next_tid	= next_tid;
 	),
 
 	TP_printk("dev %d,%d shrink transaction %u-%u(%u) freed %lu "
-		  "scanned %lu next transaction %u",
+		  "next transaction %u",
 		  MAJOR(__entry->dev), MINOR(__entry->dev),
 		  __entry->first_tid, __entry->tid, __entry->last_tid,
-		  __entry->nr_freed, __entry->nr_scanned, __entry->next_tid)
+		  __entry->nr_freed, __entry->next_tid)
 );
 
 #endif /* _TRACE_JBD2_H */