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Commit e33129d8 authored by Dan Williams's avatar Dan Williams
Browse files

md: handle_stripe5 - add request/completion logic for async write ops 



After handle_stripe5 decides whether it wants to perform a
read-modify-write, or a reconstruct write it calls
handle_write_operations5.  A read-modify-write operation will perform an
xor subtraction of the blocks marked with the R5_Wantprexor flag, copy the
new data into the stripe (biodrain) and perform a postxor operation across
all up-to-date blocks to generate the new parity.  A reconstruct write is run
when all blocks are already up-to-date in the cache so all that is needed
is a biodrain and postxor.

On the completion path STRIPE_OP_PREXOR will be set if the operation was a
read-modify-write.  The STRIPE_OP_BIODRAIN flag is used in the completion
path to differentiate write-initiated postxor operations versus
expansion-initiated postxor operations.  Completion of a write triggers i/o
to the drives.

Changelog:
* make the 'rcw' parameter to handle_write_operations5 a simple flag, Neil Brown
* remove test_and_set/test_and_clear BUG_ONs, Neil Brown

Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Acked-By: default avatarNeilBrown <neilb@suse.de>
parent d84e0f10

drivers/md/raid5.c

+138 −23
Original line number Diff line number Diff line
@@ -1822,7 +1822,79 @@ static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2) 
	}

}



static int

handle_write_operations5(struct stripe_head *sh, int rcw, int expand)

{

	int i, pd_idx = sh->pd_idx, disks = sh->disks;

	int locked = 0;



	if (rcw) {

		/* if we are not expanding this is a proper write request, and

		 * there will be bios with new data to be drained into the

		 * stripe cache

		 */

		if (!expand) {

			set_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);

			sh->ops.count++;

		}



		set_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);

		sh->ops.count++;



		for (i = disks; i--; ) {

			struct r5dev *dev = &sh->dev[i];



			if (dev->towrite) {

				set_bit(R5_LOCKED, &dev->flags);

				if (!expand)

					clear_bit(R5_UPTODATE, &dev->flags);

				locked++;

			}

		}

	} else {

		BUG_ON(!(test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags) ||

			test_bit(R5_Wantcompute, &sh->dev[pd_idx].flags)));



		set_bit(STRIPE_OP_PREXOR, &sh->ops.pending);

		set_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);

		set_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);



		sh->ops.count += 3;



		for (i = disks; i--; ) {

			struct r5dev *dev = &sh->dev[i];

			if (i == pd_idx)

				continue;



			/* For a read-modify write there may be blocks that are

			 * locked for reading while others are ready to be

			 * written so we distinguish these blocks by the

			 * R5_Wantprexor bit

			 */

			if (dev->towrite &&

			    (test_bit(R5_UPTODATE, &dev->flags) ||

			    test_bit(R5_Wantcompute, &dev->flags))) {

				set_bit(R5_Wantprexor, &dev->flags);

				set_bit(R5_LOCKED, &dev->flags);

				clear_bit(R5_UPTODATE, &dev->flags);

				locked++;

			}

		}

	}



	/* keep the parity disk locked while asynchronous operations

	 * are in flight

	 */

	set_bit(R5_LOCKED, &sh->dev[pd_idx].flags);

	clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);

	locked++;



	pr_debug("%s: stripe %llu locked: %d pending: %lx\n",

		__FUNCTION__, (unsigned long long)sh->sector,

		locked, sh->ops.pending);



	return locked;

}



/*

 * Each stripe/dev can have one or more bion attached.
@@ -2217,27 +2289,8 @@ static void handle_issuing_new_write_requests5(raid5_conf_t *conf, 
	 * we can start a write request

	 */

	if (s->locked == 0 && (rcw == 0 || rmw == 0) &&

	    !test_bit(STRIPE_BIT_DELAY, &sh->state)) {

		pr_debug("Computing parity...\n");

		compute_parity5(sh, rcw == 0 ?

			RECONSTRUCT_WRITE : READ_MODIFY_WRITE);

		/* now every locked buffer is ready to be written */

		for (i = disks; i--; )

			if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {

				pr_debug("Writing block %d\n", i);

				s->locked++;

				set_bit(R5_Wantwrite, &sh->dev[i].flags);

				if (!test_bit(R5_Insync, &sh->dev[i].flags)

				    || (i == sh->pd_idx && s->failed == 0))

					set_bit(STRIPE_INSYNC, &sh->state);

			}

		if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {

			atomic_dec(&conf->preread_active_stripes);

			if (atomic_read(&conf->preread_active_stripes) <

			    IO_THRESHOLD)

				md_wakeup_thread(conf->mddev->thread);

		}

	}

	    !test_bit(STRIPE_BIT_DELAY, &sh->state))

		s->locked += handle_write_operations5(sh, rcw == 0, 0);

}



static void handle_issuing_new_write_requests6(raid5_conf_t *conf,
@@ -2656,8 +2709,70 @@ static void handle_stripe5(struct stripe_head *sh) 
		(s.syncing && (s.uptodate < disks)) || s.expanding)

		handle_issuing_new_read_requests5(sh, &s, disks);



	/* now to consider writing and what else, if anything should be read */

	if (s.to_write)

	/* Now we check to see if any write operations have recently

	 * completed

	 */



	/* leave prexor set until postxor is done, allows us to distinguish

	 * a rmw from a rcw during biodrain

	 */

	if (test_bit(STRIPE_OP_PREXOR, &sh->ops.complete) &&

		test_bit(STRIPE_OP_POSTXOR, &sh->ops.complete)) {



		clear_bit(STRIPE_OP_PREXOR, &sh->ops.complete);

		clear_bit(STRIPE_OP_PREXOR, &sh->ops.ack);

		clear_bit(STRIPE_OP_PREXOR, &sh->ops.pending);



		for (i = disks; i--; )

			clear_bit(R5_Wantprexor, &sh->dev[i].flags);

	}



	/* if only POSTXOR is set then this is an 'expand' postxor */

	if (test_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete) &&

		test_bit(STRIPE_OP_POSTXOR, &sh->ops.complete)) {



		clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete);

		clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.ack);

		clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);



		clear_bit(STRIPE_OP_POSTXOR, &sh->ops.complete);

		clear_bit(STRIPE_OP_POSTXOR, &sh->ops.ack);

		clear_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);



		/* All the 'written' buffers and the parity block are ready to

		 * be written back to disk

		 */

		BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags));

		for (i = disks; i--; ) {

			dev = &sh->dev[i];

			if (test_bit(R5_LOCKED, &dev->flags) &&

				(i == sh->pd_idx || dev->written)) {

				pr_debug("Writing block %d\n", i);

				set_bit(R5_Wantwrite, &dev->flags);

				if (!test_and_set_bit(

				    STRIPE_OP_IO, &sh->ops.pending))

					sh->ops.count++;

				if (!test_bit(R5_Insync, &dev->flags) ||

				    (i == sh->pd_idx && s.failed == 0))

					set_bit(STRIPE_INSYNC, &sh->state);

			}

		}

		if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {

			atomic_dec(&conf->preread_active_stripes);

			if (atomic_read(&conf->preread_active_stripes) <

				IO_THRESHOLD)

				md_wakeup_thread(conf->mddev->thread);

		}

	}



	/* Now to consider new write requests and what else, if anything

	 * should be read.  We do not handle new writes when:

	 * 1/ A 'write' operation (copy+xor) is already in flight.

	 * 2/ A 'check' operation is in flight, as it may clobber the parity

	 *    block.

	 */

	if (s.to_write && !test_bit(STRIPE_OP_POSTXOR, &sh->ops.pending) &&

			  !test_bit(STRIPE_OP_CHECK, &sh->ops.pending))

		handle_issuing_new_write_requests5(conf, sh, &s, disks);



	/* maybe we need to check and possibly fix the parity for this stripe