Commit 45a4d8fd authored by ChangSyun Peng's avatar ChangSyun Peng Committed by Song Liu
Browse files

md/raid5: Allow degraded raid6 to do rmw 



Degraded raid6 always do reconstruct-write now. With raid6 xor supported,
we can do rmw in degraded raid6. This patch can reduce many read IOs to
improve performance.

If the failed disk is P, Q or the disk we want to write to, we may need to
do reconstruct-write in max degraded raid6. In this situation we can not
read enough data from handle_stripe_dirtying() so we have to set force_rcw
in handle_stripe_fill() to read all data.

Reviewed-by: default avatarAlex Wu <alexwu@synology.com>
Reviewed-by: default avatarBingJing Chang <bingjingc@synology.com>
Reviewed-by: default avatarDanny Shih <dannyshih@synology.com>
Signed-off-by: default avatarChangSyun Peng <allenpeng@synology.com>
Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
parent a1c6ae3d

drivers/md/raid5.c

+16 −6
Original line number Diff line number Diff line
@@ -3557,6 +3557,7 @@ static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s, 
	struct r5dev *fdev[2] = { &sh->dev[s->failed_num[0]],

				  &sh->dev[s->failed_num[1]] };

	int i;

	bool force_rcw = (sh->raid_conf->rmw_level == PARITY_DISABLE_RMW);





	if (test_bit(R5_LOCKED, &dev->flags) ||
@@ -3615,18 +3616,27 @@ static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s, 
			 * devices must be read.

			 */

			return 1;



		if (s->failed >= 2 &&

		    (fdev[i]->towrite ||

		     s->failed_num[i] == sh->pd_idx ||

		     s->failed_num[i] == sh->qd_idx) &&

		    !test_bit(R5_UPTODATE, &fdev[i]->flags))

			/* In max degraded raid6, If the failed disk is P, Q,

			 * or we want to read the failed disk, we need to do

			 * reconstruct-write.

			 */

			force_rcw = true;

	}



	/* If we are forced to do a reconstruct-write, either because

	 * the current RAID6 implementation only supports that, or

	 * because parity cannot be trusted and we are currently

	 * recovering it, there is extra need to be careful.

	/* If we are forced to do a reconstruct-write, because parity

	 * cannot be trusted and we are currently recovering it, there

	 * is extra need to be careful.

	 * If one of the devices that we would need to read, because

	 * it is not being overwritten (and maybe not written at all)

	 * is missing/faulty, then we need to read everything we can.

	 */

	if (sh->raid_conf->level != 6 &&

	    sh->raid_conf->rmw_level != PARITY_DISABLE_RMW &&

	if (!force_rcw &&

	    sh->sector < sh->raid_conf->mddev->recovery_cp)

		/* reconstruct-write isn't being forced */

		return 0;

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