bcache: A block layer cache

Does writethrough and writeback caching, handles unclean shutdown, and
has a bunch of other nifty features motivated by real world usage.

See the wiki at http://bcache.evilpiepirate.org for more.

Signed-off-by: Kent Overstreet <koverstreet@google.com>

1 files changed, 390 insertions, 0 deletions

diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
new file mode 100644
index 000000000000..f565512f6fac
--- /dev/null
+++ b/drivers/md/bcache/io.c
@@ -0,0 +1,390 @@
+/*
+ * Some low level IO code, and hacks for various block layer limitations
+ *
+ * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
+ * Copyright 2012 Google, Inc.
+ */
+
+#include "bcache.h"
+#include "bset.h"
+#include "debug.h"
+
+static void bch_bi_idx_hack_endio(struct bio *bio, int error)
+{
+	struct bio *p = bio->bi_private;
+
+	bio_endio(p, error);
+	bio_put(bio);
+}
+
+static void bch_generic_make_request_hack(struct bio *bio)
+{
+	if (bio->bi_idx) {
+		struct bio *clone = bio_alloc(GFP_NOIO, bio_segments(bio));
+
+		memcpy(clone->bi_io_vec,
+		       bio_iovec(bio),
+		       bio_segments(bio) * sizeof(struct bio_vec));
+
+		clone->bi_sector	= bio->bi_sector;
+		clone->bi_bdev		= bio->bi_bdev;
+		clone->bi_rw		= bio->bi_rw;
+		clone->bi_vcnt		= bio_segments(bio);
+		clone->bi_size		= bio->bi_size;
+
+		clone->bi_private	= bio;
+		clone->bi_end_io	= bch_bi_idx_hack_endio;
+
+		bio = clone;
+	}
+
+	generic_make_request(bio);
+}
+
+/**
+ * bch_bio_split - split a bio
+ * @bio:	bio to split
+ * @sectors:	number of sectors to split from the front of @bio
+ * @gfp:	gfp mask
+ * @bs:		bio set to allocate from
+ *
+ * Allocates and returns a new bio which represents @sectors from the start of
+ * @bio, and updates @bio to represent the remaining sectors.
+ *
+ * If bio_sectors(@bio) was less than or equal to @sectors, returns @bio
+ * unchanged.
+ *
+ * The newly allocated bio will point to @bio's bi_io_vec, if the split was on a
+ * bvec boundry; it is the caller's responsibility to ensure that @bio is not
+ * freed before the split.
+ *
+ * If bch_bio_split() is running under generic_make_request(), it's not safe to
+ * allocate more than one bio from the same bio set. Therefore, if it is running
+ * under generic_make_request() it masks out __GFP_WAIT when doing the
+ * allocation. The caller must check for failure if there's any possibility of
+ * it being called from under generic_make_request(); it is then the caller's
+ * responsibility to retry from a safe context (by e.g. punting to workqueue).
+ */
+struct bio *bch_bio_split(struct bio *bio, int sectors,
+			  gfp_t gfp, struct bio_set *bs)
+{
+	unsigned idx = bio->bi_idx, vcnt = 0, nbytes = sectors << 9;
+	struct bio_vec *bv;
+	struct bio *ret = NULL;
+
+	BUG_ON(sectors <= 0);
+
+	/*
+	 * If we're being called from underneath generic_make_request() and we
+	 * already allocated any bios from this bio set, we risk deadlock if we
+	 * use the mempool. So instead, we possibly fail and let the caller punt
+	 * to workqueue or somesuch and retry in a safe context.
+	 */
+	if (current->bio_list)
+		gfp &= ~__GFP_WAIT;
+
+	if (sectors >= bio_sectors(bio))
+		return bio;
+
+	if (bio->bi_rw & REQ_DISCARD) {
+		ret = bio_alloc_bioset(gfp, 1, bs);
+		idx = 0;
+		goto out;
+	}
+
+	bio_for_each_segment(bv, bio, idx) {
+		vcnt = idx - bio->bi_idx;
+
+		if (!nbytes) {
+			ret = bio_alloc_bioset(gfp, vcnt, bs);
+			if (!ret)
+				return NULL;
+
+			memcpy(ret->bi_io_vec, bio_iovec(bio),
+			       sizeof(struct bio_vec) * vcnt);
+
+			break;
+		} else if (nbytes < bv->bv_len) {
+			ret = bio_alloc_bioset(gfp, ++vcnt, bs);
+			if (!ret)
+				return NULL;
+
+			memcpy(ret->bi_io_vec, bio_iovec(bio),
+			       sizeof(struct bio_vec) * vcnt);
+
+			ret->bi_io_vec[vcnt - 1].bv_len = nbytes;
+			bv->bv_offset	+= nbytes;
+			bv->bv_len	-= nbytes;
+			break;
+		}
+
+		nbytes -= bv->bv_len;
+	}
+out:
+	ret->bi_bdev	= bio->bi_bdev;
+	ret->bi_sector	= bio->bi_sector;
+	ret->bi_size	= sectors << 9;
+	ret->bi_rw	= bio->bi_rw;
+	ret->bi_vcnt	= vcnt;
+	ret->bi_max_vecs = vcnt;
+
+	bio->bi_sector	+= sectors;
+	bio->bi_size	-= sectors << 9;
+	bio->bi_idx	 = idx;
+
+	if (bio_integrity(bio)) {
+		if (bio_integrity_clone(ret, bio, gfp)) {
+			bio_put(ret);
+			return NULL;
+		}
+
+		bio_integrity_trim(ret, 0, bio_sectors(ret));
+		bio_integrity_trim(bio, bio_sectors(ret), bio_sectors(bio));
+	}
+
+	return ret;
+}
+
+static unsigned bch_bio_max_sectors(struct bio *bio)
+{
+	unsigned ret = bio_sectors(bio);
+	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
+	struct bio_vec *bv, *end = bio_iovec(bio) +
+		min_t(int, bio_segments(bio), queue_max_segments(q));
+
+	struct bvec_merge_data bvm = {
+		.bi_bdev	= bio->bi_bdev,
+		.bi_sector	= bio->bi_sector,
+		.bi_size	= 0,
+		.bi_rw		= bio->bi_rw,
+	};
+
+	if (bio->bi_rw & REQ_DISCARD)
+		return min(ret, q->limits.max_discard_sectors);
+
+	if (bio_segments(bio) > queue_max_segments(q) ||
+	    q->merge_bvec_fn) {
+		ret = 0;
+
+		for (bv = bio_iovec(bio); bv < end; bv++) {
+			if (q->merge_bvec_fn &&
+			    q->merge_bvec_fn(q, &bvm, bv) < (int) bv->bv_len)
+				break;
+
+			ret		+= bv->bv_len >> 9;
+			bvm.bi_size	+= bv->bv_len;
+		}
+
+		if (ret >= (BIO_MAX_PAGES * PAGE_SIZE) >> 9)
+			return (BIO_MAX_PAGES * PAGE_SIZE) >> 9;
+	}
+
+	ret = min(ret, queue_max_sectors(q));
+
+	WARN_ON(!ret);
+	ret = max_t(int, ret, bio_iovec(bio)->bv_len >> 9);
+
+	return ret;
+}
+
+static void bch_bio_submit_split_done(struct closure *cl)
+{
+	struct bio_split_hook *s = container_of(cl, struct bio_split_hook, cl);
+
+	s->bio->bi_end_io = s->bi_end_io;
+	s->bio->bi_private = s->bi_private;
+	bio_endio(s->bio, 0);
+
+	closure_debug_destroy(&s->cl);
+	mempool_free(s, s->p->bio_split_hook);
+}
+
+static void bch_bio_submit_split_endio(struct bio *bio, int error)
+{
+	struct closure *cl = bio->bi_private;
+	struct bio_split_hook *s = container_of(cl, struct bio_split_hook, cl);
+
+	if (error)
+		clear_bit(BIO_UPTODATE, &s->bio->bi_flags);
+
+	bio_put(bio);
+	closure_put(cl);
+}
+
+static void __bch_bio_submit_split(struct closure *cl)
+{
+	struct bio_split_hook *s = container_of(cl, struct bio_split_hook, cl);
+	struct bio *bio = s->bio, *n;
+
+	do {
+		n = bch_bio_split(bio, bch_bio_max_sectors(bio),
+				  GFP_NOIO, s->p->bio_split);
+		if (!n)
+			continue_at(cl, __bch_bio_submit_split, system_wq);
+
+		n->bi_end_io	= bch_bio_submit_split_endio;
+		n->bi_private	= cl;
+
+		closure_get(cl);
+		bch_generic_make_request_hack(n);
+	} while (n != bio);
+
+	continue_at(cl, bch_bio_submit_split_done, NULL);
+}
+
+void bch_generic_make_request(struct bio *bio, struct bio_split_pool *p)
+{
+	struct bio_split_hook *s;
+
+	if (!bio_has_data(bio) && !(bio->bi_rw & REQ_DISCARD))
+		goto submit;
+
+	if (bio_sectors(bio) <= bch_bio_max_sectors(bio))
+		goto submit;
+
+	s = mempool_alloc(p->bio_split_hook, GFP_NOIO);
+
+	s->bio		= bio;
+	s->p		= p;
+	s->bi_end_io	= bio->bi_end_io;
+	s->bi_private	= bio->bi_private;
+	bio_get(bio);
+
+	closure_call(&s->cl, __bch_bio_submit_split, NULL, NULL);
+	return;
+submit:
+	bch_generic_make_request_hack(bio);
+}
+
+/* Bios with headers */
+
+void bch_bbio_free(struct bio *bio, struct cache_set *c)
+{
+	struct bbio *b = container_of(bio, struct bbio, bio);
+	mempool_free(b, c->bio_meta);
+}
+
+struct bio *bch_bbio_alloc(struct cache_set *c)
+{
+	struct bbio *b = mempool_alloc(c->bio_meta, GFP_NOIO);
+	struct bio *bio = &b->bio;
+
+	bio_init(bio);
+	bio->bi_flags		|= BIO_POOL_NONE << BIO_POOL_OFFSET;
+	bio->bi_max_vecs	 = bucket_pages(c);
+	bio->bi_io_vec		 = bio->bi_inline_vecs;
+
+	return bio;
+}
+
+void __bch_submit_bbio(struct bio *bio, struct cache_set *c)
+{
+	struct bbio *b = container_of(bio, struct bbio, bio);
+
+	bio->bi_sector	= PTR_OFFSET(&b->key, 0);
+	bio->bi_bdev	= PTR_CACHE(c, &b->key, 0)->bdev;
+
+	b->submit_time_us = local_clock_us();
+	closure_bio_submit(bio, bio->bi_private, PTR_CACHE(c, &b->key, 0));
+}
+
+void bch_submit_bbio(struct bio *bio, struct cache_set *c,
+		     struct bkey *k, unsigned ptr)
+{
+	struct bbio *b = container_of(bio, struct bbio, bio);
+	bch_bkey_copy_single_ptr(&b->key, k, ptr);
+	__bch_submit_bbio(bio, c);
+}
+
+/* IO errors */
+
+void bch_count_io_errors(struct cache *ca, int error, const char *m)
+{
+	/*
+	 * The halflife of an error is:
+	 * log2(1/2)/log2(127/128) * refresh ~= 88 * refresh
+	 */
+
+	if (ca->set->error_decay) {
+		unsigned count = atomic_inc_return(&ca->io_count);
+
+		while (count > ca->set->error_decay) {
+			unsigned errors;
+			unsigned old = count;
+			unsigned new = count - ca->set->error_decay;
+
+			/*
+			 * First we subtract refresh from count; each time we
+			 * succesfully do so, we rescale the errors once:
+			 */
+
+			count = atomic_cmpxchg(&ca->io_count, old, new);
+
+			if (count == old) {
+				count = new;
+
+				errors = atomic_read(&ca->io_errors);
+				do {
+					old = errors;
+					new = ((uint64_t) errors * 127) / 128;
+					errors = atomic_cmpxchg(&ca->io_errors,
+								old, new);
+				} while (old != errors);
+			}
+		}
+	}
+
+	if (error) {
+		char buf[BDEVNAME_SIZE];
+		unsigned errors = atomic_add_return(1 << IO_ERROR_SHIFT,
+						    &ca->io_errors);
+		errors >>= IO_ERROR_SHIFT;
+
+		if (errors < ca->set->error_limit)
+			pr_err("%s: IO error on %s, recovering",
+			       bdevname(ca->bdev, buf), m);
+		else
+			bch_cache_set_error(ca->set,
+					    "%s: too many IO errors %s",
+					    bdevname(ca->bdev, buf), m);
+	}
+}
+
+void bch_bbio_count_io_errors(struct cache_set *c, struct bio *bio,
+			      int error, const char *m)
+{
+	struct bbio *b = container_of(bio, struct bbio, bio);
+	struct cache *ca = PTR_CACHE(c, &b->key, 0);
+
+	unsigned threshold = bio->bi_rw & REQ_WRITE
+		? c->congested_write_threshold_us
+		: c->congested_read_threshold_us;
+
+	if (threshold) {
+		unsigned t = local_clock_us();
+
+		int us = t - b->submit_time_us;
+		int congested = atomic_read(&c->congested);
+
+		if (us > (int) threshold) {
+			int ms = us / 1024;
+			c->congested_last_us = t;
+
+			ms = min(ms, CONGESTED_MAX + congested);
+			atomic_sub(ms, &c->congested);
+		} else if (congested < 0)
+			atomic_inc(&c->congested);
+	}
+
+	bch_count_io_errors(ca, error, m);
+}
+
+void bch_bbio_endio(struct cache_set *c, struct bio *bio,
+		    int error, const char *m)
+{
+	struct closure *cl = bio->bi_private;
+
+	bch_bbio_count_io_errors(c, bio, error, m);
+	bio_put(bio);
+	closure_put(cl);
+}