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Commit 0472a42b authored by NeilBrown's avatar NeilBrown Committed by Shaohua Li
Browse files

md/raid5: remove over-loading of ->bi_phys_segments. 



When a read request, which bypassed the cache, fails, we need to retry
it through the cache.
This involves attaching it to a sequence of stripe_heads, and it may not
be possible to get all the stripe_heads we need at once.
We do what we can, and record how far we got in ->bi_phys_segments so
we can pick up again later.

There is only ever one bio which may have a non-zero offset stored in
->bi_phys_segments, the one that is either active in the single thread
which calls retry_aligned_read(), or is in conf->retry_read_aligned
waiting for retry_aligned_read() to be called again.

So we only need to store one offset value.  This can be in a local
variable passed between remove_bio_from_retry() and
retry_aligned_read(), or in the r5conf structure next to the
->retry_read_aligned pointer.

Storing it there allows the last usage of ->bi_phys_segments to be
removed from md/raid5.c.

Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarShaohua Li <shli@fb.com>
parent 016c76ac

drivers/md/raid5.c

+12 −12
Original line number Diff line number Diff line
@@ -5082,12 +5082,14 @@ static void add_bio_to_retry(struct bio *bi,struct r5conf *conf) 
	md_wakeup_thread(conf->mddev->thread);

}



static struct bio *remove_bio_from_retry(struct r5conf *conf)

static struct bio *remove_bio_from_retry(struct r5conf *conf,

					 unsigned int *offset)

{

	struct bio *bi;



	bi = conf->retry_read_aligned;

	if (bi) {

		*offset = conf->retry_read_offset;

		conf->retry_read_aligned = NULL;

		return bi;

	}
@@ -5095,11 +5097,7 @@ static struct bio *remove_bio_from_retry(struct r5conf *conf) 
	if(bi) {

		conf->retry_read_aligned_list = bi->bi_next;

		bi->bi_next = NULL;

		/*

		 * this sets the active strip count to 1 and the processed

		 * strip count to zero (upper 8 bits)

		 */

		raid5_set_bi_processed_stripes(bi, 0);

		*offset = 0;

	}



	return bi;
@@ -6055,7 +6053,8 @@ static inline sector_t raid5_sync_request(struct mddev *mddev, sector_t sector_n 
	return STRIPE_SECTORS;

}



static int  retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)

static int  retry_aligned_read(struct r5conf *conf, struct bio *raid_bio,

			       unsigned int offset)

{

	/* We may not be able to submit a whole bio at once as there

	 * may not be enough stripe_heads available.
@@ -6084,7 +6083,7 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio) 
		     sector += STRIPE_SECTORS,

		     scnt++) {



		if (scnt < raid5_bi_processed_stripes(raid_bio))

		if (scnt < offset)

			/* already done this stripe */

			continue;
@@ -6092,15 +6091,15 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio) 


		if (!sh) {

			/* failed to get a stripe - must wait */

			raid5_set_bi_processed_stripes(raid_bio, scnt);

			conf->retry_read_aligned = raid_bio;

			conf->retry_read_offset = scnt;

			return handled;

		}



		if (!add_stripe_bio(sh, raid_bio, dd_idx, 0, 0)) {

			raid5_release_stripe(sh);

			raid5_set_bi_processed_stripes(raid_bio, scnt);

			conf->retry_read_aligned = raid_bio;

			conf->retry_read_offset = scnt;

			return handled;

		}
@@ -6228,6 +6227,7 @@ static void raid5d(struct md_thread *thread) 
	while (1) {

		struct bio *bio;

		int batch_size, released;

		unsigned int offset;



		released = release_stripe_list(conf, conf->temp_inactive_list);

		if (released)
@@ -6245,10 +6245,10 @@ static void raid5d(struct md_thread *thread) 
		}

		raid5_activate_delayed(conf);



		while ((bio = remove_bio_from_retry(conf))) {

		while ((bio = remove_bio_from_retry(conf, &offset))) {

			int ok;

			spin_unlock_irq(&conf->device_lock);

			ok = retry_aligned_read(conf, bio);

			ok = retry_aligned_read(conf, bio, offset);

			spin_lock_irq(&conf->device_lock);

			if (!ok)

				break;

drivers/md/raid5.h

+1 −29
Original line number Diff line number Diff line
@@ -487,35 +487,6 @@ static inline struct bio *r5_next_bio(struct bio *bio, sector_t sector) 
		return NULL;

}



/*

 * We maintain a count of processed stripes in the upper 16 bits

 */

static inline int raid5_bi_processed_stripes(struct bio *bio)

{

	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;



	return (atomic_read(segments) >> 16) & 0xffff;

}



static inline void raid5_set_bi_processed_stripes(struct bio *bio,

	unsigned int cnt)

{

	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;

	int old, new;



	do {

		old = atomic_read(segments);

		new = (old & 0xffff) | (cnt << 16);

	} while (atomic_cmpxchg(segments, old, new) != old);

}



static inline void raid5_set_bi_stripes(struct bio *bio, unsigned int cnt)

{

	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;



	atomic_set(segments, cnt);

}



/* NOTE NR_STRIPE_HASH_LOCKS must remain below 64.

 * This is because we sometimes take all the spinlocks

 * and creating that much locking depth can cause
@@ -613,6 +584,7 @@ struct r5conf { 
	struct list_head	delayed_list; /* stripes that have plugged requests */

	struct list_head	bitmap_list; /* stripes delaying awaiting bitmap update */

	struct bio		*retry_read_aligned; /* currently retrying aligned bios   */

	unsigned int		retry_read_offset; /* sector offset into retry_read_aligned */

	struct bio		*retry_read_aligned_list; /* aligned bios retry list  */

	atomic_t		preread_active_stripes; /* stripes with scheduled io */

	atomic_t		active_aligned_reads;