text: /*
   * Moving/copying garbage collector
   *
   * Copyright 2012 Google, Inc.
   */
  
  #include "bcache.h"
  #include "btree.h"
  #include "debug.h"
  #include "request.h"
  
  #include <trace/events/bcache.h>
  
  struct moving_io {
  	struct closure		cl;
  	struct keybuf_key	*w;
  	struct data_insert_op	op;
  	struct bbio		bio;
  };
  
  static bool moving_pred(struct keybuf *buf, struct bkey *k)
  {
  	struct cache_set *c = container_of(buf, struct cache_set,
  					   moving_gc_keys);
  	unsigned i;
  
  	for (i = 0; i < KEY_PTRS(k); i++)
  		if (ptr_available(c, k, i) &&
  		    GC_MOVE(PTR_BUCKET(c, k, i)))
  			return true;
  
  	return false;
  }
  
  /* Moving GC - IO loop */
  
  static void moving_io_destructor(struct closure *cl)
  {
  	struct moving_io *io = container_of(cl, struct moving_io, cl);
  	kfree(io);
  }
  
  static void write_moving_finish(struct closure *cl)
  {
  	struct moving_io *io = container_of(cl, struct moving_io, cl);
  	struct bio *bio = &io->bio.bio;
  	struct bio_vec *bv;
  	int i;
  
  	bio_for_each_segment_all(bv, bio, i)
  		__free_page(bv->bv_page);
  
  	if (io->op.replace_collision)
  		trace_bcache_gc_copy_collision(&io->w->key);
  
  	bch_keybuf_del(&io->op.c->moving_gc_keys, io->w);
  
  	up(&io->op.c->moving_in_flight);
  
  	closure_return_with_destructor(cl, moving_io_destructor);
  }
  
  static void read_moving_endio(struct bio *bio, int error)
  {
  	struct bbio *b = container_of(bio, struct bbio, bio);
  	struct moving_io *io = container_of(bio->bi_private,
  					    struct moving_io, cl);
  
  	if (error)
  		io->op.error = error;
  	else if (!KEY_DIRTY(&b->key) &&
  		 ptr_stale(io->op.c, &b->key, 0)) {
  		io->op.error = -EINTR;
  	}
  
  	bch_bbio_endio(io->op.c, bio, error, "reading data to move");
  }
  
  static void moving_init(struct moving_io *io)
  {
  	struct bio *bio = &io->bio.bio;
  
  	bio_init(bio);
  	bio_get(bio);
  	bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
  
  	bio->bi_iter.bi_size	= KEY_SIZE(&io->w->key) << 9;
  	bio->bi_max_vecs	= DIV_ROUND_UP(KEY_SIZE(&io->w->key),
  					       PAGE_SECTORS);
  	bio->bi_private		= &io->cl;
  	bio->bi_io_vec		= bio->bi_inline_vecs;
  	bch_bio_map(bio, NULL);
  }
  
  static void write_moving(struct closure *cl)
  {
  	struct moving_io *io = container_of(cl, struct moving_io, cl);
  	struct data_insert_op *op = &io->op;
  
  	if (!op->error) {
  		moving_init(io);
  
  		io->bio.bio.bi_iter.bi_sector = KEY_START(&io->w->key);
  		op->write_prio		= 1;
  		op->bio			= &io->bio.bio;
  
  		op->writeback		= KEY_DIRTY(&io->w->key);
  		op->csum		= KEY_CSUM(&io->w->key);
  
  		bkey_copy(&op->replace_key, &io->w->key);
  		op->replace		= true;
  
  		closure_call(&op->cl, bch_data_insert, NULL, cl);
  	}
  
  	continue_at(cl, write_moving_finish, op->wq);
  }
  
  static void read_moving_submit(struct closure *cl)
  {
  	struct moving_io *io = container_of(cl, struct moving_io, cl);
  	struct bio *bio = &io->bio.bio;
  
  	bch_submit_bbio(bio, io->op.c, &io->w->key, 0);
  
  	continue_at(cl, write_moving, io->op.wq);
  }
  
  static void read_moving(struct cache_set *c)
  {
  	struct keybuf_key *w;
  	struct moving_io *io;
  	struct bio *bio;
  	struct closure cl;
  
  	closure_init_stack(&cl);
  
  	/* XXX: if we error, background writeback could stall indefinitely */
  
  	while (!test_bit(CACHE_SET_STOPPING, &c->flags)) {
  		w = bch_keybuf_next_rescan(c, &c->moving_gc_keys,
  					   &MAX_KEY, moving_pred);
  		if (!w)
  			break;
  
  		if (ptr_stale(c, &w->key, 0)) {
  			bch_keybuf_del(&c->moving_gc_keys, w);
  			continue;
  		}
  
  		io = kzalloc(sizeof(struct moving_io) + sizeof(struct bio_vec)
  			     * DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
  			     GFP_KERNEL);
  		if (!io)
  			goto err;
  
  		w->private	= io;
  		io->w		= w;
  		io->op.inode	= KEY_INODE(&w->key);
  		io->op.c	= c;
  		io->op.wq	= c->moving_gc_wq;
  
  		moving_init(io);
  		bio = &io->bio.bio;
  
  		bio->bi_rw	= READ;
  		bio->bi_end_io	= read_moving_endio;
  
  		if (bio_alloc_pages(bio, GFP_KERNEL))
  			goto err;
  
  		trace_bcache_gc_copy(&w->key);
  
  		down(&c->moving_in_flight);
  		closure_call(&io->cl, read_moving_submit, NULL, &cl);
  	}
  
  	if (0) {
  err:		if (!IS_ERR_OR_NULL(w->private))
  			kfree(w->private);
  
  		bch_keybuf_del(&c->moving_gc_keys, w);
  	}
  
  	closure_sync(&cl);
  }
  
  static bool bucket_cmp(struct bucket *l, struct bucket *r)
  {
  	return GC_SECTORS_USED(l) < GC_SECTORS_USED(r);
  }
  
  static unsigned bucket_heap_top(struct cache *ca)
  {
  	struct bucket *b;
  	return (b = heap_peek(&ca->heap)) ? GC_SECTORS_USED(b) : 0;
  }
  
  void bch_moving_gc(struct cache_set *c)
  {
  	struct cache *ca;
  	struct bucket *b;
  	unsigned i;
  
  	if (!c->copy_gc_enabled)
  		return;
  
  	mutex_lock(&c->bucket_lock);
  
  	for_each_cache(ca, c, i) {
  		unsigned sectors_to_move = 0;
  		unsigned reserve_sectors = ca->sb.bucket_size *
  			fifo_used(&ca->free[RESERVE_MOVINGGC]);
  
  		ca->heap.used = 0;
  
  		for_each_bucket(b, ca) {
  			if (GC_MARK(b) == GC_MARK_METADATA ||
  			    !GC_SECTORS_USED(b) ||
  			    GC_SECTORS_USED(b) == ca->sb.bucket_size ||
  			    atomic_read(&b->pin))
  				continue;
  
  			if (!heap_full(&ca->heap)) {
  				sectors_to_move += GC_SECTORS_USED(b);
  				heap_add(&ca->heap, b, bucket_cmp);
  			} else if (bucket_cmp(b, heap_peek(&ca->heap))) {
  				sectors_to_move -= bucket_heap_top(ca);
  				sectors_to_move += GC_SECTORS_USED(b);
  
  				ca->heap.data[0] = b;
  				heap_sift(&ca->heap, 0, bucket_cmp);
  			}
  		}
  
  		while (sectors_to_move > reserve_sectors) {
  			heap_pop(&ca->heap, b, bucket_cmp);
  			sectors_to_move -= GC_SECTORS_USED(b);
  		}
  
  		while (heap_pop(&ca->heap, b, bucket_cmp))
  			SET_GC_MOVE(b, 1);
  	}
  
  	mutex_unlock(&c->bucket_lock);
  
  	c->moving_gc_keys.last_scanned = ZERO_KEY;
  
  	read_moving(c);
  }
  
  void bch_moving_init_cache_set(struct cache_set *c)
  {
  	bch_keybuf_init(&c->moving_gc_keys);
  	sema_init(&c->moving_in_flight, 64);
  }
  