linux-kernel - [RFC][PATCH] dm: Remove dm_bufio_cond

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Message-ID: <20160913084520.GA5012@twins.programming.kicks-ass.net>
Date:   Tue, 13 Sep 2016 10:45:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Mikulas Patocka <mpatocka@...hat.com>,
        linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: [RFC][PATCH] dm: Remove dm_bufio_cond_resched()

Hi all,

While grepping for PREEMPT_VOLUNTARY I ran into dm_bufio_cond_resched()
and wondered WTH it was about.

Is there anything wrong with the below patch?

---
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 8625040bae92..125aedc3875f 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -191,19 +191,6 @@ static void dm_bufio_unlock(struct dm_bufio_client *c)
 	mutex_unlock(&c->lock);
 }
 
-/*
- * FIXME Move to sched.h?
- */
-#ifdef CONFIG_PREEMPT_VOLUNTARY
-#  define dm_bufio_cond_resched()		\
-do {						\
-	if (unlikely(need_resched()))		\
-		_cond_resched();		\
-} while (0)
-#else
-#  define dm_bufio_cond_resched()                do { } while (0)
-#endif
-
 /*----------------------------------------------------------------*/
 
 /*
@@ -741,7 +728,7 @@ static void __flush_write_list(struct list_head *write_list)
 			list_entry(write_list->next, struct dm_buffer, write_list);
 		list_del(&b->write_list);
 		submit_io(b, WRITE, b->block, write_endio);
-		dm_bufio_cond_resched();
+		cond_resched();
 	}
 	blk_finish_plug(&plug);
 }
@@ -780,7 +767,7 @@ static struct dm_buffer *__get_unclaimed_buffer(struct dm_bufio_client *c)
 			__unlink_buffer(b);
 			return b;
 		}
-		dm_bufio_cond_resched();
+		cond_resched();
 	}
 
 	list_for_each_entry_reverse(b, &c->lru[LIST_DIRTY], lru_list) {
@@ -791,7 +778,7 @@ static struct dm_buffer *__get_unclaimed_buffer(struct dm_bufio_client *c)
 			__unlink_buffer(b);
 			return b;
 		}
-		dm_bufio_cond_resched();
+		cond_resched();
 	}
 
 	return NULL;
@@ -923,7 +910,7 @@ static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait,
 			return;
 
 		__write_dirty_buffer(b, write_list);
-		dm_bufio_cond_resched();
+		cond_resched();
 	}
 }
 
@@ -973,7 +960,7 @@ static void __check_watermark(struct dm_bufio_client *c,
 			return;
 
 		__free_buffer_wake(b);
-		dm_bufio_cond_resched();
+		cond_resched();
 	}
 
 	if (c->n_buffers[LIST_DIRTY] > threshold_buffers)
@@ -1170,7 +1157,7 @@ void dm_bufio_prefetch(struct dm_bufio_client *c,
 				submit_io(b, READ, b->block, read_endio);
 			dm_bufio_release(b);
 
-			dm_bufio_cond_resched();
+			cond_resched();
 
 			if (!n_blocks)
 				goto flush_plug;
@@ -1291,7 +1278,7 @@ int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c)
 		    !test_bit(B_WRITING, &b->state))
 			__relink_lru(b, LIST_CLEAN);
 
-		dm_bufio_cond_resched();
+		cond_resched();
 
 		/*
 		 * If we dropped the lock, the list is no longer consistent,
@@ -1574,7 +1561,7 @@ static unsigned long __scan(struct dm_bufio_client *c, unsigned long nr_to_scan,
 				freed++;
 			if (!--nr_to_scan || ((count - freed) <= retain_target))
 				return freed;
-			dm_bufio_cond_resched();
+			cond_resched();
 		}
 	}
 	return freed;
@@ -1808,7 +1795,7 @@ static void __evict_old_buffers(struct dm_bufio_client *c, unsigned long age_hz)
 		if (__try_evict_buffer(b, 0))
 			count--;
 
-		dm_bufio_cond_resched();
+		cond_resched();
 	}
 
 	dm_bufio_unlock(c);