raid5: remove unnecessary bitmap write optimization

PATCH In review Shaohua Li 2 participants 2 messages Jul 4, 2012 MD RAID

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Shaohua Li

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2012-07-04 05:21 UTC #0 lore raw

PATCH v2 2/3 raid5: remove unnecessary bitmap write optimization

Neil pointed out the bitmap write optimization in handle_stripe_clean_event() is unnecessary, because the chance one stripe gets written twice in the mean time is rare. We can always do a bitmap_startwrite when a write request is added to a stripe and bitmap_endwrite after write request is done. Delete the optimization. With it, we can delete some cases of device_lock.

Signed-off-by Shaohua Li <[email protected]>

---
 drivers/md/raid5.c |   21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

drivers/md/raid5.c +9 ~~-12~~

Index: linux/drivers/md/raid5.c
===================================================================
@@ -2350,7 +2350,7 @@ static int add_stripe_bio(struct stripe_
 	spin_lock_irq(&conf->device_lock);
 	if (forwrite) {
 		bip = &sh->dev[dd_idx].towrite;
-		if (*bip == NULL && sh->dev[dd_idx].written == NULL)
+		if (*bip == NULL)
 			firstwrite = 1;
 	} else
 		bip = &sh->dev[dd_idx].toread;

@@ -2455,6 +2455,7 @@ handle_failed_stripe(struct r5conf *conf
 			s->to_write--;
 			bitmap_end = 1;
 		}
+		spin_unlock_irq(&conf->device_lock);
 
 		if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
 			wake_up(&conf->wait_for_overlap);

@@ -2470,6 +2471,10 @@ handle_failed_stripe(struct r5conf *conf
 			}
 			bi = nextbi;
 		}
+		if (bitmap_end)
+			bitmap_endwrite(conf->mddev->bitmap, sh->sector,
+				STRIPE_SECTORS, 0, 0);
+		bitmap_end = 0;
 		/* and fail all 'written' */
 		bi = sh->dev[i].written;
 		sh->dev[i].written = NULL;

@@ -2509,7 +2514,6 @@ handle_failed_stripe(struct r5conf *conf
 				bi = nextbi;
 			}
 		}
-		spin_unlock_irq(&conf->device_lock);
 		if (bitmap_end)
 			bitmap_endwrite(conf->mddev->bitmap, sh->sector,
 					STRIPE_SECTORS, 0, 0);

@@ -2713,9 +2717,7 @@ static void handle_stripe_clean_event(st
 				test_bit(R5_UPTODATE, &dev->flags)) {
 				/* We can return any write requests */
 				struct bio *wbi, *wbi2;
-				int bitmap_end = 0;
 				pr_debug("Return write for disc %d\n", i);
-				spin_lock_irq(&conf->device_lock);
 				wbi = dev->written;
 				dev->written = NULL;
 				while (wbi && wbi->bi_sector <

@@ -2728,15 +2730,10 @@ static void handle_stripe_clean_event(st
 					}
 					wbi = wbi2;
 				}
-				if (dev->towrite == NULL)
-					bitmap_end = 1;
-				spin_unlock_irq(&conf->device_lock);
-				if (bitmap_end)
-					bitmap_endwrite(conf->mddev->bitmap,
-							sh->sector,
-							STRIPE_SECTORS,
+				bitmap_endwrite(conf->mddev->bitmap, sh->sector,
+						STRIPE_SECTORS,
 					 !test_bit(STRIPE_DEGRADED, &sh->state),
-							0);
+						0);
 			}
 		}

NeilBrown

2012-07-04 06:17 UTC #1 lore raw

Quoted 7 lines · On Wed, 4 Jul 2012 13:21:43 +0800 Shaohua Li <[email protected]> wrote:

Neil pointed out the bitmap write optimization in handle_stripe_clean_event() is unnecessary, because the chance one stripe gets written twice in the mean time is rare. We can always do a bitmap_startwrite when a write request is added to a stripe and bitmap_endwrite after write request is done. Delete the optimization. With it, we can delete some cases of device_lock.
Signed-off-by Shaohua Li <[email protected]>

Thanks. I've applied all three of these.
However...

drivers/md/raid5.c handle_failed_stripe(struct r5conf *conf · line 2461

Quoted 8 lines

drivers/md/raid5.c +1 -0

@@ -2455,6 +2455,7 @@ handle_failed_stripe(struct r5conf *conf
 			s->to_write--;
 			bitmap_end = 1;
 		}
+		spin_unlock_irq(&conf->device_lock);
 
 		if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
 			wake_up(&conf->wait_for_overlap);

I moved that spin_unlock_irq a little bit further up.

Thanks,
NeilBrown