bcachefs: Split out alloc_background.c

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

21 files changed, 843 insertions, 815 deletions

diff --git a/fs/bcachefs/Makefile b/fs/bcachefs/Makefile
index 13cd6d2cdc91..5318287c5ac4 100644
--- a/fs/bcachefs/Makefile
+++ b/fs/bcachefs/Makefile
@@ -3,7 +3,8 @@ obj-$(CONFIG_BCACHEFS_FS)	+= bcachefs.o
 
 bcachefs-y		:=	\
 	acl.o			\
-	alloc.o			\
+	alloc_background.o	\
+	alloc_foreground.o	\
 	bkey.o			\
 	bkey_methods.o		\
 	bset.o			\
diff --git a/fs/bcachefs/alloc.c b/fs/bcachefs/alloc_background.c
index 73c11f808edc..d22b2b72b0d1 100644
--- a/fs/bcachefs/alloc.c
+++ b/fs/bcachefs/alloc_background.c
@@ -1,79 +1,19 @@
-/*
- * Primary bucket allocation code
- *
- * Copyright 2012 Google, Inc.
- *
- * Allocation in bcache is done in terms of buckets:
- *
- * Each bucket has associated an 8 bit gen; this gen corresponds to the gen in
- * btree pointers - they must match for the pointer to be considered valid.
- *
- * Thus (assuming a bucket has no dirty data or metadata in it) we can reuse a
- * bucket simply by incrementing its gen.
- *
- * The gens (along with the priorities; it's really the gens are important but
- * the code is named as if it's the priorities) are written in an arbitrary list
- * of buckets on disk, with a pointer to them in the journal header.
- *
- * When we invalidate a bucket, we have to write its new gen to disk and wait
- * for that write to complete before we use it - otherwise after a crash we
- * could have pointers that appeared to be good but pointed to data that had
- * been overwritten.
- *
- * Since the gens and priorities are all stored contiguously on disk, we can
- * batch this up: We fill up the free_inc list with freshly invalidated buckets,
- * call prio_write(), and when prio_write() finishes we pull buckets off the
- * free_inc list and optionally discard them.
- *
- * free_inc isn't the only freelist - if it was, we'd often have to sleep while
- * priorities and gens were being written before we could allocate. c->free is a
- * smaller freelist, and buckets on that list are always ready to be used.
- *
- * If we've got discards enabled, that happens when a bucket moves from the
- * free_inc list to the free list.
- *
- * It's important to ensure that gens don't wrap around - with respect to
- * either the oldest gen in the btree or the gen on disk. This is quite
- * difficult to do in practice, but we explicitly guard against it anyways - if
- * a bucket is in danger of wrapping around we simply skip invalidating it that
- * time around, and we garbage collect or rewrite the priorities sooner than we
- * would have otherwise.
- *
- * bch2_bucket_alloc() allocates a single bucket from a specific device.
- *
- * bch2_bucket_alloc_set() allocates one or more buckets from different devices
- * in a given filesystem.
- *
- * invalidate_buckets() drives all the processes described above. It's called
- * from bch2_bucket_alloc() and a few other places that need to make sure free
- * buckets are ready.
- *
- * invalidate_buckets_(lru|fifo)() find buckets that are available to be
- * invalidated, and then invalidate them and stick them on the free_inc list -
- * in either lru or fifo order.
- */
-
+// SPDX-License-Identifier: GPL-2.0
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_background.h"
+#include "alloc_foreground.h"
 #include "btree_cache.h"
 #include "btree_io.h"
 #include "btree_update.h"
 #include "btree_update_interior.h"
 #include "btree_gc.h"
 #include "buckets.h"
-#include "checksum.h"
 #include "clock.h"
 #include "debug.h"
-#include "disk_groups.h"
 #include "error.h"
-#include "extents.h"
-#include "io.h"
-#include "journal.h"
 #include "journal_io.h"
-#include "super-io.h"
 #include "trace.h"
 
-#include <linux/blkdev.h>
 #include <linux/kthread.h>
 #include <linux/math64.h>
 #include <linux/random.h>
@@ -496,23 +436,6 @@ static void bch2_bucket_clock_init(struct bch_fs *c, int rw)
  * commands to the newly free buckets, then puts them on the various freelists.
  */
 
-static void verify_not_on_freelist(struct bch_fs *c, struct bch_dev *ca,
-				   size_t bucket)
-{
-	if (expensive_debug_checks(c) &&
-	    test_bit(BCH_FS_ALLOCATOR_STARTED, &c->flags)) {
-		size_t iter;
-		long i;
-		unsigned j;
-
-		for (j = 0; j < RESERVE_NR; j++)
-			fifo_for_each_entry(i, &ca->free[j], iter)
-				BUG_ON(i == bucket);
-		fifo_for_each_entry(i, &ca->free_inc, iter)
-			BUG_ON(i == bucket);
-	}
-}
-
 #define BUCKET_GC_GEN_MAX	96U
 
 /**
@@ -1044,668 +967,6 @@ stop:
 	return 0;
 }
 
-/* Allocation */
-
-/*
- * Open buckets represent a bucket that's currently being allocated from.  They
- * serve two purposes:
- *
- *  - They track buckets that have been partially allocated, allowing for
- *    sub-bucket sized allocations - they're used by the sector allocator below
- *
- *  - They provide a reference to the buckets they own that mark and sweep GC
- *    can find, until the new allocation has a pointer to it inserted into the
- *    btree
- *
- * When allocating some space with the sector allocator, the allocation comes
- * with a reference to an open bucket - the caller is required to put that
- * reference _after_ doing the index update that makes its allocation reachable.
- */
-
-void __bch2_open_bucket_put(struct bch_fs *c, struct open_bucket *ob)
-{
-	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);
-
-	percpu_down_read(&c->usage_lock);
-	spin_lock(&ob->lock);
-
-	bch2_mark_alloc_bucket(c, ca, PTR_BUCKET_NR(ca, &ob->ptr),
-			       false, gc_pos_alloc(c, ob), 0);
-	ob->valid = false;
-
-	spin_unlock(&ob->lock);
-	percpu_up_read(&c->usage_lock);
-
-	spin_lock(&c->freelist_lock);
-	ob->freelist = c->open_buckets_freelist;
-	c->open_buckets_freelist = ob - c->open_buckets;
-	c->open_buckets_nr_free++;
-	spin_unlock(&c->freelist_lock);
-
-	closure_wake_up(&c->open_buckets_wait);
-}
-
-static struct open_bucket *bch2_open_bucket_alloc(struct bch_fs *c)
-{
-	struct open_bucket *ob;
-
-	BUG_ON(!c->open_buckets_freelist || !c->open_buckets_nr_free);
-
-	ob = c->open_buckets + c->open_buckets_freelist;
-	c->open_buckets_freelist = ob->freelist;
-	atomic_set(&ob->pin, 1);
-
-	c->open_buckets_nr_free--;
-	return ob;
-}
-
-/* _only_ for allocating the journal on a new device: */
-long bch2_bucket_alloc_new_fs(struct bch_dev *ca)
-{
-	struct bucket_array *buckets;
-	ssize_t b;
-
-	rcu_read_lock();
-	buckets = bucket_array(ca);
-
-	for (b = ca->mi.first_bucket; b < ca->mi.nbuckets; b++)
-		if (is_available_bucket(buckets->b[b].mark))
-			goto success;
-	b = -1;
-success:
-	rcu_read_unlock();
-	return b;
-}
-
-static inline unsigned open_buckets_reserved(enum alloc_reserve reserve)
-{
-	switch (reserve) {
-	case RESERVE_ALLOC:
-		return 0;
-	case RESERVE_BTREE:
-		return BTREE_NODE_RESERVE / 2;
-	default:
-		return BTREE_NODE_RESERVE;
-	}
-}
-
-/**
- * bch_bucket_alloc - allocate a single bucket from a specific device
- *
- * Returns index of bucket on success, 0 on failure
- * */
-int bch2_bucket_alloc(struct bch_fs *c, struct bch_dev *ca,
-		      enum alloc_reserve reserve,
-		      bool may_alloc_partial,
-		      struct closure *cl)
-{
-	struct bucket_array *buckets;
-	struct open_bucket *ob;
-	long bucket;
-
-	spin_lock(&c->freelist_lock);
-
-	if (may_alloc_partial &&
-	    ca->open_buckets_partial_nr) {
-		int ret = ca->open_buckets_partial[--ca->open_buckets_partial_nr];
-		c->open_buckets[ret].on_partial_list = false;
-		spin_unlock(&c->freelist_lock);
-		return ret;
-	}
-
-	if (unlikely(c->open_buckets_nr_free <= open_buckets_reserved(reserve))) {
-		if (cl)
-			closure_wait(&c->open_buckets_wait, cl);
-		spin_unlock(&c->freelist_lock);
-		trace_open_bucket_alloc_fail(ca, reserve);
-		return OPEN_BUCKETS_EMPTY;
-	}
-
-	if (likely(fifo_pop(&ca->free[RESERVE_NONE], bucket)))
-		goto out;
-
-	switch (reserve) {
-	case RESERVE_ALLOC:
-		if (fifo_pop(&ca->free[RESERVE_BTREE], bucket))
-			goto out;
-		break;
-	case RESERVE_BTREE:
-		if (fifo_used(&ca->free[RESERVE_BTREE]) * 2 >=
-		    ca->free[RESERVE_BTREE].size &&
-		    fifo_pop(&ca->free[RESERVE_BTREE], bucket))
-			goto out;
-		break;
-	case RESERVE_MOVINGGC:
-		if (fifo_pop(&ca->free[RESERVE_MOVINGGC], bucket))
-			goto out;
-		break;
-	default:
-		break;
-	}
-
-	if (cl)
-		closure_wait(&c->freelist_wait, cl);
-
-	spin_unlock(&c->freelist_lock);
-
-	trace_bucket_alloc_fail(ca, reserve);
-	return FREELIST_EMPTY;
-out:
-	verify_not_on_freelist(c, ca, bucket);
-
-	ob = bch2_open_bucket_alloc(c);
-
-	spin_lock(&ob->lock);
-	buckets = bucket_array(ca);
-
-	ob->valid	= true;
-	ob->sectors_free = ca->mi.bucket_size;
-	ob->ptr		= (struct bch_extent_ptr) {
-		.gen	= buckets->b[bucket].mark.gen,
-		.offset	= bucket_to_sector(ca, bucket),
-		.dev	= ca->dev_idx,
-	};
-
-	bucket_io_clock_reset(c, ca, bucket, READ);
-	bucket_io_clock_reset(c, ca, bucket, WRITE);
-	spin_unlock(&ob->lock);
-
-	spin_unlock(&c->freelist_lock);
-
-	bch2_wake_allocator(ca);
-
-	trace_bucket_alloc(ca, reserve);
-	return ob - c->open_buckets;
-}
-
-static int __dev_alloc_cmp(struct write_point *wp,
-			   unsigned l, unsigned r)
-{
-	return ((wp->next_alloc[l] > wp->next_alloc[r]) -
-		(wp->next_alloc[l] < wp->next_alloc[r]));
-}
-
-#define dev_alloc_cmp(l, r) __dev_alloc_cmp(wp, l, r)
-
-struct dev_alloc_list bch2_wp_alloc_list(struct bch_fs *c,
-					 struct write_point *wp,
-					 struct bch_devs_mask *devs)
-{
-	struct dev_alloc_list ret = { .nr = 0 };
-	struct bch_dev *ca;
-	unsigned i;
-
-	for_each_member_device_rcu(ca, c, i, devs)
-		ret.devs[ret.nr++] = i;
-
-	bubble_sort(ret.devs, ret.nr, dev_alloc_cmp);
-	return ret;
-}
-
-void bch2_wp_rescale(struct bch_fs *c, struct bch_dev *ca,
-		     struct write_point *wp)
-{
-	u64 *v = wp->next_alloc + ca->dev_idx;
-	u64 free_space = dev_buckets_free(c, ca);
-	u64 free_space_inv = free_space
-		? div64_u64(1ULL << 48, free_space)
-		: 1ULL << 48;
-	u64 scale = *v / 4;
-
-	if (*v + free_space_inv >= *v)
-		*v += free_space_inv;
-	else
-		*v = U64_MAX;
-
-	for (v = wp->next_alloc;
-	     v < wp->next_alloc + ARRAY_SIZE(wp->next_alloc); v++)
-		*v = *v < scale ? 0 : *v - scale;
-}
-
-static enum bucket_alloc_ret bch2_bucket_alloc_set(struct bch_fs *c,
-					struct write_point *wp,
-					unsigned nr_replicas,
-					enum alloc_reserve reserve,
-					struct bch_devs_mask *devs,
-					struct closure *cl)
-{
-	enum bucket_alloc_ret ret = NO_DEVICES;
-	struct dev_alloc_list devs_sorted;
-	struct bch_dev *ca;
-	unsigned i, nr_ptrs_effective = 0;
-	bool have_cache_dev = false;
-
-	BUG_ON(nr_replicas > ARRAY_SIZE(wp->ptrs));
-
-	for (i = wp->first_ptr; i < wp->nr_ptrs; i++) {
-		ca = bch_dev_bkey_exists(c, wp->ptrs[i]->ptr.dev);
-
-		nr_ptrs_effective += ca->mi.durability;
-		have_cache_dev |= !ca->mi.durability;
-	}
-
-	if (nr_ptrs_effective >= nr_replicas)
-		return ALLOC_SUCCESS;
-
-	devs_sorted = bch2_wp_alloc_list(c, wp, devs);
-
-	for (i = 0; i < devs_sorted.nr; i++) {
-		int ob;
-
-		ca = rcu_dereference(c->devs[devs_sorted.devs[i]]);
-		if (!ca)
-			continue;
-
-		if (!ca->mi.durability &&
-		    (have_cache_dev ||
-		     wp->type != BCH_DATA_USER))
-			continue;
-
-		ob = bch2_bucket_alloc(c, ca, reserve,
-				       wp->type == BCH_DATA_USER, cl);
-		if (ob < 0) {
-			ret = ob;
-			if (ret == OPEN_BUCKETS_EMPTY)
-				break;
-			continue;
-		}
-
-		BUG_ON(ob <= 0 || ob > U8_MAX);
-		BUG_ON(wp->nr_ptrs >= ARRAY_SIZE(wp->ptrs));
-
-		wp->ptrs[wp->nr_ptrs++] = c->open_buckets + ob;
-
-		bch2_wp_rescale(c, ca, wp);
-
-		nr_ptrs_effective += ca->mi.durability;
-		have_cache_dev |= !ca->mi.durability;
-
-		__clear_bit(ca->dev_idx, devs->d);
-
-		if (nr_ptrs_effective >= nr_replicas) {
-			ret = ALLOC_SUCCESS;
-			break;
-		}
-	}
-
-	EBUG_ON(reserve == RESERVE_MOVINGGC &&
-		ret != ALLOC_SUCCESS &&
-		ret != OPEN_BUCKETS_EMPTY);
-
-	switch (ret) {
-	case ALLOC_SUCCESS:
-		return 0;
-	case NO_DEVICES:
-		return -EROFS;
-	case FREELIST_EMPTY:
-	case OPEN_BUCKETS_EMPTY:
-		return cl ? -EAGAIN : -ENOSPC;
-	default:
-		BUG();
-	}
-}
-
-/* Sector allocator */
-
-static void writepoint_drop_ptr(struct bch_fs *c,
-				struct write_point *wp,
-				unsigned i)
-{
-	struct open_bucket *ob = wp->ptrs[i];
-	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);
-
-	BUG_ON(ca->open_buckets_partial_nr >=
-	       ARRAY_SIZE(ca->open_buckets_partial));
-
-	if (wp->type == BCH_DATA_USER) {
-		spin_lock(&c->freelist_lock);
-		ob->on_partial_list = true;
-		ca->open_buckets_partial[ca->open_buckets_partial_nr++] =
-			ob - c->open_buckets;
-		spin_unlock(&c->freelist_lock);
-
-		closure_wake_up(&c->open_buckets_wait);
-		closure_wake_up(&c->freelist_wait);
-	} else {
-		bch2_open_bucket_put(c, ob);
-	}
-
-	array_remove_item(wp->ptrs, wp->nr_ptrs, i);
-
-	if (i < wp->first_ptr)
-		wp->first_ptr--;
-}
-
-static void writepoint_drop_ptrs(struct bch_fs *c,
-				 struct write_point *wp,
-				 u16 target, bool in_target)
-{
-	int i;
-
-	for (i = wp->first_ptr - 1; i >= 0; --i)
-		if (bch2_dev_in_target(c, wp->ptrs[i]->ptr.dev,
-				       target) == in_target)
-			writepoint_drop_ptr(c, wp, i);
-}
-
-static void verify_not_stale(struct bch_fs *c, const struct write_point *wp)
-{
-#ifdef CONFIG_BCACHEFS_DEBUG
-	struct open_bucket *ob;
-	unsigned i;
-
-	writepoint_for_each_ptr_all(wp, ob, i) {
-		struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);
-
-		BUG_ON(ptr_stale(ca, &ob->ptr));
-	}
-#endif
-}
-
-static int open_bucket_add_buckets(struct bch_fs *c,
-				   u16 target,
-				   struct write_point *wp,
-				   struct bch_devs_list *devs_have,
-				   unsigned nr_replicas,
-				   enum alloc_reserve reserve,
-				   struct closure *cl)
-{
-	struct bch_devs_mask devs = c->rw_devs[wp->type];
-	const struct bch_devs_mask *t;
-	struct open_bucket *ob;
-	unsigned i;
-	int ret;
-
-	percpu_down_read(&c->usage_lock);
-	rcu_read_lock();
-
-	/* Don't allocate from devices we already have pointers to: */
-	for (i = 0; i < devs_have->nr; i++)
-		__clear_bit(devs_have->devs[i], devs.d);
-
-	writepoint_for_each_ptr_all(wp, ob, i)
-		__clear_bit(ob->ptr.dev, devs.d);
-
-	t = bch2_target_to_mask(c, target);
-	if (t)
-		bitmap_and(devs.d, devs.d, t->d, BCH_SB_MEMBERS_MAX);
-
-	ret = bch2_bucket_alloc_set(c, wp, nr_replicas, reserve, &devs, cl);
-
-	rcu_read_unlock();
-	percpu_up_read(&c->usage_lock);
-
-	return ret;
-}
-
-static struct write_point *__writepoint_find(struct hlist_head *head,
-					     unsigned long write_point)
-{
-	struct write_point *wp;
-
-	hlist_for_each_entry_rcu(wp, head, node)
-		if (wp->write_point == write_point)
-			return wp;
-
-	return NULL;
-}
-
-static struct hlist_head *writepoint_hash(struct bch_fs *c,
-					  unsigned long write_point)
-{
-	unsigned hash =
-		hash_long(write_point, ilog2(ARRAY_SIZE(c->write_points_hash)));
-
-	return &c->write_points_hash[hash];
-}
-
-static struct write_point *writepoint_find(struct bch_fs *c,
-					   unsigned long write_point)
-{
-	struct write_point *wp, *oldest;
-	struct hlist_head *head;
-
-	if (!(write_point & 1UL)) {
-		wp = (struct write_point *) write_point;
-		mutex_lock(&wp->lock);
-		return wp;
-	}
-
-	head = writepoint_hash(c, write_point);
-restart_find:
-	wp = __writepoint_find(head, write_point);
-	if (wp) {
-lock_wp:
-		mutex_lock(&wp->lock);
-		if (wp->write_point == write_point)
-			goto out;
-		mutex_unlock(&wp->lock);
-		goto restart_find;
-	}
-
-	oldest = NULL;
-	for (wp = c->write_points;
-	     wp < c->write_points + ARRAY_SIZE(c->write_points);
-	     wp++)
-		if (!oldest || time_before64(wp->last_used, oldest->last_used))
-			oldest = wp;
-
-	mutex_lock(&oldest->lock);
-	mutex_lock(&c->write_points_hash_lock);
-	wp = __writepoint_find(head, write_point);
-	if (wp && wp != oldest) {
-		mutex_unlock(&c->write_points_hash_lock);
-		mutex_unlock(&oldest->lock);
-		goto lock_wp;
-	}
-
-	wp = oldest;
-	hlist_del_rcu(&wp->node);
-	wp->write_point = write_point;
-	hlist_add_head_rcu(&wp->node, head);
-	mutex_unlock(&c->write_points_hash_lock);
-out:
-	wp->last_used = sched_clock();
-	return wp;
-}
-
-/*
- * Get us an open_bucket we can allocate from, return with it locked:
- */
-struct write_point *bch2_alloc_sectors_start(struct bch_fs *c,
-				unsigned target,
-				struct write_point_specifier write_point,
-				struct bch_devs_list *devs_have,
-				unsigned nr_replicas,
-				unsigned nr_replicas_required,
-				enum alloc_reserve reserve,
-				unsigned flags,
-				struct closure *cl)
-{
-	struct write_point *wp;
-	struct open_bucket *ob;
-	struct bch_dev *ca;
-	unsigned nr_ptrs_have, nr_ptrs_effective;
-	int ret, i, cache_idx = -1;
-
-	BUG_ON(!nr_replicas || !nr_replicas_required);
-
-	wp = writepoint_find(c, write_point.v);
-
-	wp->first_ptr = 0;
-
-	/* does writepoint have ptrs we can't use? */
-	writepoint_for_each_ptr(wp, ob, i)
-		if (bch2_dev_list_has_dev(*devs_have, ob->ptr.dev)) {
-			swap(wp->ptrs[i], wp->ptrs[wp->first_ptr]);
-			wp->first_ptr++;
-		}
-
-	nr_ptrs_have = wp->first_ptr;
-
-	/* does writepoint have ptrs we don't want to use? */
-	if (target)
-		writepoint_for_each_ptr(wp, ob, i)
-			if (!bch2_dev_in_target(c, ob->ptr.dev, target)) {
-				swap(wp->ptrs[i], wp->ptrs[wp->first_ptr]);
-				wp->first_ptr++;
-			}
-
-	if (flags & BCH_WRITE_ONLY_SPECIFIED_DEVS) {
-		ret = open_bucket_add_buckets(c, target, wp, devs_have,
-					      nr_replicas, reserve, cl);
-	} else {
-		ret = open_bucket_add_buckets(c, target, wp, devs_have,
-					      nr_replicas, reserve, NULL);
-		if (!ret)
-			goto alloc_done;
-
-		wp->first_ptr = nr_ptrs_have;
-
-		ret = open_bucket_add_buckets(c, 0, wp, devs_have,
-					      nr_replicas, reserve, cl);
-	}
-
-	if (ret && ret != -EROFS)
-		goto err;
-alloc_done:
-	/* check for more than one cache: */
-	for (i = wp->nr_ptrs - 1; i >= wp->first_ptr; --i) {
-		ca = bch_dev_bkey_exists(c, wp->ptrs[i]->ptr.dev);
-
-		if (ca->mi.durability)
-			continue;
-
-		/*
-		 * if we ended up with more than one cache device, prefer the
-		 * one in the target we want:
-		 */
-		if (cache_idx >= 0) {
-			if (!bch2_dev_in_target(c, wp->ptrs[i]->ptr.dev,
-						target)) {
-				writepoint_drop_ptr(c, wp, i);
-			} else {
-				writepoint_drop_ptr(c, wp, cache_idx);
-				cache_idx = i;
-			}
-		} else {
-			cache_idx = i;
-		}
-	}
-
-	/* we might have more effective replicas than required: */
-	nr_ptrs_effective = 0;
-	writepoint_for_each_ptr(wp, ob, i) {
-		ca = bch_dev_bkey_exists(c, ob->ptr.dev);
-		nr_ptrs_effective += ca->mi.durability;
-	}
-
-	if (ret == -EROFS &&
-	    nr_ptrs_effective >= nr_replicas_required)
-		ret = 0;
-
-	if (ret)
-		goto err;
-
-	if (nr_ptrs_effective > nr_replicas) {
-		writepoint_for_each_ptr(wp, ob, i) {
-			ca = bch_dev_bkey_exists(c, ob->ptr.dev);
-
-			if (ca->mi.durability &&
-			    ca->mi.durability <= nr_ptrs_effective - nr_replicas &&
-			    !bch2_dev_in_target(c, ob->ptr.dev, target)) {
-				swap(wp->ptrs[i], wp->ptrs[wp->first_ptr]);
-				wp->first_ptr++;
-				nr_ptrs_effective -= ca->mi.durability;
-			}
-		}
-	}
-
-	if (nr_ptrs_effective > nr_replicas) {
-		writepoint_for_each_ptr(wp, ob, i) {
-			ca = bch_dev_bkey_exists(c, ob->ptr.dev);
-
-			if (ca->mi.durability &&
-			    ca->mi.durability <= nr_ptrs_effective - nr_replicas) {
-				swap(wp->ptrs[i], wp->ptrs[wp->first_ptr]);
-				wp->first_ptr++;
-				nr_ptrs_effective -= ca->mi.durability;
-			}
-		}
-	}
-
-	/* Remove pointers we don't want to use: */
-	if (target)
-		writepoint_drop_ptrs(c, wp, target, false);
-
-	BUG_ON(wp->first_ptr >= wp->nr_ptrs);
-	BUG_ON(nr_ptrs_effective < nr_replicas_required);
-
-	wp->sectors_free = UINT_MAX;
-
-	writepoint_for_each_ptr(wp, ob, i)
-		wp->sectors_free = min(wp->sectors_free, ob->sectors_free);
-
-	BUG_ON(!wp->sectors_free || wp->sectors_free == UINT_MAX);
-
-	verify_not_stale(c, wp);
-
-	return wp;
-err:
-	mutex_unlock(&wp->lock);
-	return ERR_PTR(ret);
-}
-
-/*
- * Append pointers to the space we just allocated to @k, and mark @sectors space
- * as allocated out of @ob
- */
-void bch2_alloc_sectors_append_ptrs(struct bch_fs *c, struct write_point *wp,
-				    struct bkey_i_extent *e, unsigned sectors)
-{
-	struct open_bucket *ob;
-	unsigned i;
-
-	BUG_ON(sectors > wp->sectors_free);
-	wp->sectors_free -= sectors;
-
-	writepoint_for_each_ptr(wp, ob, i) {
-		struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);
-		struct bch_extent_ptr tmp = ob->ptr;
-
-		EBUG_ON(bch2_extent_has_device(extent_i_to_s_c(e), ob->ptr.dev));
-
-		tmp.cached = bkey_extent_is_cached(&e->k) ||
-			(!ca->mi.durability && wp->type == BCH_DATA_USER);
-
-		tmp.offset += ca->mi.bucket_size - ob->sectors_free;
-		extent_ptr_append(e, tmp);
-
-		BUG_ON(sectors > ob->sectors_free);
-		ob->sectors_free -= sectors;
-	}
-}
-
-/*
- * Append pointers to the space we just allocated to @k, and mark @sectors space
- * as allocated out of @ob
- */
-void bch2_alloc_sectors_done(struct bch_fs *c, struct write_point *wp)
-{
-	int i;
-
-	for (i = wp->nr_ptrs - 1; i >= 0; --i) {
-		struct open_bucket *ob = wp->ptrs[i];
-
-		if (!ob->sectors_free) {
-			array_remove_item(wp->ptrs, wp->nr_ptrs, i);
-			bch2_open_bucket_put(c, ob);
-		}
-	}
-
-	mutex_unlock(&wp->lock);
-}
-
 /* Startup/shutdown (ro/rw): */
 
 void bch2_recalc_capacity(struct bch_fs *c)
@@ -1792,19 +1053,6 @@ void bch2_recalc_capacity(struct bch_fs *c)
 	closure_wake_up(&c->freelist_wait);
 }
 
-static void bch2_stop_write_point(struct bch_fs *c, struct bch_dev *ca,
-				  struct write_point *wp)
-{
-	struct bch_devs_mask not_self;
-
-	bitmap_complement(not_self.d, ca->self.d, BCH_SB_MEMBERS_MAX);
-
-	mutex_lock(&wp->lock);
-	wp->first_ptr = wp->nr_ptrs;
-	writepoint_drop_ptrs(c, wp, dev_to_target(ca->dev_idx), true);
-	mutex_unlock(&wp->lock);
-}
-
 static bool bch2_dev_has_open_write_point(struct bch_fs *c, struct bch_dev *ca)
 {
 	struct open_bucket *ob;
@@ -1842,11 +1090,11 @@ void bch2_dev_allocator_remove(struct bch_fs *c, struct bch_dev *ca)
 
 	/* Next, close write points that point to this device... */
 	for (i = 0; i < ARRAY_SIZE(c->write_points); i++)
-		bch2_stop_write_point(c, ca, &c->write_points[i]);
+		bch2_writepoint_stop(c, ca, &c->write_points[i]);
 
-	bch2_stop_write_point(c, ca, &ca->copygc_write_point);
-	bch2_stop_write_point(c, ca, &c->rebalance_write_point);
-	bch2_stop_write_point(c, ca, &c->btree_write_point);
+	bch2_writepoint_stop(c, ca, &ca->copygc_write_point);
+	bch2_writepoint_stop(c, ca, &c->rebalance_write_point);
+	bch2_writepoint_stop(c, ca, &c->btree_write_point);
 
 	mutex_lock(&c->btree_reserve_cache_lock);
 	while (c->btree_reserve_cache_nr) {
diff --git a/fs/bcachefs/alloc_background.h b/fs/bcachefs/alloc_background.h
new file mode 100644
index 000000000000..6dbabe83cab7
--- /dev/null
+++ b/fs/bcachefs/alloc_background.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_ALLOC_BACKGROUND_H
+#define _BCACHEFS_ALLOC_BACKGROUND_H
+
+#include "bcachefs.h"
+#include "alloc_types.h"
+#include "debug.h"
+
+#define ALLOC_SCAN_BATCH(ca)		((ca)->mi.nbuckets >> 9)
+
+const char *bch2_alloc_invalid(const struct bch_fs *, struct bkey_s_c);
+int bch2_alloc_to_text(struct bch_fs *, char *, size_t, struct bkey_s_c);
+
+#define bch2_bkey_alloc_ops (struct bkey_ops) {		\
+	.key_invalid	= bch2_alloc_invalid,		\
+	.val_to_text	= bch2_alloc_to_text,		\
+}
+
+int bch2_alloc_read(struct bch_fs *, struct list_head *);
+int bch2_alloc_replay_key(struct bch_fs *, struct bpos);
+
+static inline void bch2_wake_allocator(struct bch_dev *ca)
+{
+	struct task_struct *p;
+
+	rcu_read_lock();
+	p = rcu_dereference(ca->alloc_thread);
+	if (p)
+		wake_up_process(p);
+	rcu_read_unlock();
+}
+
+static inline void verify_not_on_freelist(struct bch_fs *c, struct bch_dev *ca,
+					  size_t bucket)
+{
+	if (expensive_debug_checks(c) &&
+	    test_bit(BCH_FS_ALLOCATOR_STARTED, &c->flags)) {
+		size_t iter;
+		long i;
+		unsigned j;
+
+		for (j = 0; j < RESERVE_NR; j++)
+			fifo_for_each_entry(i, &ca->free[j], iter)
+				BUG_ON(i == bucket);
+		fifo_for_each_entry(i, &ca->free_inc, iter)
+			BUG_ON(i == bucket);
+	}
+}
+
+void bch2_recalc_capacity(struct bch_fs *);
+
+void bch2_dev_allocator_remove(struct bch_fs *, struct bch_dev *);
+void bch2_dev_allocator_add(struct bch_fs *, struct bch_dev *);
+
+void bch2_dev_allocator_stop(struct bch_dev *);
+int bch2_dev_allocator_start(struct bch_dev *);
+
+int bch2_alloc_write(struct bch_fs *);
+int bch2_fs_allocator_start(struct bch_fs *);
+void bch2_fs_allocator_init(struct bch_fs *);
+
+#endif /* _BCACHEFS_ALLOC_BACKGROUND_H */
diff --git a/fs/bcachefs/alloc_foreground.c b/fs/bcachefs/alloc_foreground.c
new file mode 100644
index 000000000000..be25e01a7d00
--- /dev/null
+++ b/fs/bcachefs/alloc_foreground.c
@@ -0,0 +1,741 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Primary bucket allocation code
+ *
+ * Copyright 2012 Google, Inc.
+ *
+ * Allocation in bcache is done in terms of buckets:
+ *
+ * Each bucket has associated an 8 bit gen; this gen corresponds to the gen in
+ * btree pointers - they must match for the pointer to be considered valid.
+ *
+ * Thus (assuming a bucket has no dirty data or metadata in it) we can reuse a
+ * bucket simply by incrementing its gen.
+ *
+ * The gens (along with the priorities; it's really the gens are important but
+ * the code is named as if it's the priorities) are written in an arbitrary list
+ * of buckets on disk, with a pointer to them in the journal header.
+ *
+ * When we invalidate a bucket, we have to write its new gen to disk and wait
+ * for that write to complete before we use it - otherwise after a crash we
+ * could have pointers that appeared to be good but pointed to data that had
+ * been overwritten.
+ *
+ * Since the gens and priorities are all stored contiguously on disk, we can
+ * batch this up: We fill up the free_inc list with freshly invalidated buckets,
+ * call prio_write(), and when prio_write() finishes we pull buckets off the
+ * free_inc list and optionally discard them.
+ *
+ * free_inc isn't the only freelist - if it was, we'd often have to sleep while
+ * priorities and gens were being written before we could allocate. c->free is a
+ * smaller freelist, and buckets on that list are always ready to be used.
+ *
+ * If we've got discards enabled, that happens when a bucket moves from the
+ * free_inc list to the free list.
+ *
+ * It's important to ensure that gens don't wrap around - with respect to
+ * either the oldest gen in the btree or the gen on disk. This is quite
+ * difficult to do in practice, but we explicitly guard against it anyways - if
+ * a bucket is in danger of wrapping around we simply skip invalidating it that
+ * time around, and we garbage collect or rewrite the priorities sooner than we
+ * would have otherwise.
+ *
+ * bch2_bucket_alloc() allocates a single bucket from a specific device.
+ *
+ * bch2_bucket_alloc_set() allocates one or more buckets from different devices
+ * in a given filesystem.
+ *
+ * invalidate_buckets() drives all the processes described above. It's called
+ * from bch2_bucket_alloc() and a few other places that need to make sure free
+ * buckets are ready.
+ *
+ * invalidate_buckets_(lru|fifo)() find buckets that are available to be
+ * invalidated, and then invalidate them and stick them on the free_inc list -
+ * in either lru or fifo order.
+ */
+
+#include "bcachefs.h"
+#include "alloc_background.h"
+#include "alloc_foreground.h"
+#include "btree_gc.h"
+#include "buckets.h"
+#include "clock.h"
+#include "debug.h"
+#include "disk_groups.h"
+#include "io.h"
+#include "trace.h"
+
+#include <linux/math64.h>
+#include <linux/rculist.h>
+#include <linux/rcupdate.h>
+
+enum bucket_alloc_ret {
+	ALLOC_SUCCESS		= 0,
+	OPEN_BUCKETS_EMPTY	= -1,
+	FREELIST_EMPTY		= -2,	/* Allocator thread not keeping up */
+	NO_DEVICES		= -3,	/* -EROFS */
+};
+
+/*
+ * Open buckets represent a bucket that's currently being allocated from.  They
+ * serve two purposes:
+ *
+ *  - They track buckets that have been partially allocated, allowing for
+ *    sub-bucket sized allocations - they're used by the sector allocator below
+ *
+ *  - They provide a reference to the buckets they own that mark and sweep GC
+ *    can find, until the new allocation has a pointer to it inserted into the
+ *    btree
+ *
+ * When allocating some space with the sector allocator, the allocation comes
+ * with a reference to an open bucket - the caller is required to put that
+ * reference _after_ doing the index update that makes its allocation reachable.
+ */
+
+void __bch2_open_bucket_put(struct bch_fs *c, struct open_bucket *ob)
+{
+	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);
+
+	percpu_down_read(&c->usage_lock);
+	spin_lock(&ob->lock);
+
+	bch2_mark_alloc_bucket(c, ca, PTR_BUCKET_NR(ca, &ob->ptr),
+			       false, gc_pos_alloc(c, ob), 0);
+	ob->valid = false;
+
+	spin_unlock(&ob->lock);
+	percpu_up_read(&c->usage_lock);
+
+	spin_lock(&c->freelist_lock);
+	ob->freelist = c->open_buckets_freelist;
+	c->open_buckets_freelist = ob - c->open_buckets;
+	c->open_buckets_nr_free++;
+	spin_unlock(&c->freelist_lock);
+
+	closure_wake_up(&c->open_buckets_wait);
+}
+
+static struct open_bucket *bch2_open_bucket_alloc(struct bch_fs *c)
+{
+	struct open_bucket *ob;
+
+	BUG_ON(!c->open_buckets_freelist || !c->open_buckets_nr_free);
+
+	ob = c->open_buckets + c->open_buckets_freelist;
+	c->open_buckets_freelist = ob->freelist;
+	atomic_set(&ob->pin, 1);
+
+	c->open_buckets_nr_free--;
+	return ob;
+}
+
+/* _only_ for allocating the journal on a new device: */
+long bch2_bucket_alloc_new_fs(struct bch_dev *ca)
+{
+	struct bucket_array *buckets;
+	ssize_t b;
+
+	rcu_read_lock();
+	buckets = bucket_array(ca);
+
+	for (b = ca->mi.first_bucket; b < ca->mi.nbuckets; b++)
+		if (is_available_bucket(buckets->b[b].mark))
+			goto success;
+	b = -1;
+success:
+	rcu_read_unlock();
+	return b;
+}
+
+static inline unsigned open_buckets_reserved(enum alloc_reserve reserve)
+{
+	switch (reserve) {
+	case RESERVE_ALLOC:
+		return 0;
+	case RESERVE_BTREE:
+		return BTREE_NODE_RESERVE / 2;
+	default:
+		return BTREE_NODE_RESERVE;
+	}
+}
+
+/**
+ * bch_bucket_alloc - allocate a single bucket from a specific device
+ *
+ * Returns index of bucket on success, 0 on failure
+ * */
+int bch2_bucket_alloc(struct bch_fs *c, struct bch_dev *ca,
+		      enum alloc_reserve reserve,
+		      bool may_alloc_partial,
+		      struct closure *cl)
+{
+	struct bucket_array *buckets;
+	struct open_bucket *ob;
+	long bucket;
+
+	spin_lock(&c->freelist_lock);
+
+	if (may_alloc_partial &&
+	    ca->open_buckets_partial_nr) {
+		int ret = ca->open_buckets_partial[--ca->open_buckets_partial_nr];
+		c->open_buckets[ret].on_partial_list = false;
+		spin_unlock(&c->freelist_lock);
+		return ret;
+	}
+
+	if (unlikely(c->open_buckets_nr_free <= open_buckets_reserved(reserve))) {
+		if (cl)
+			closure_wait(&c->open_buckets_wait, cl);
+		spin_unlock(&c->freelist_lock);
+		trace_open_bucket_alloc_fail(ca, reserve);
+		return OPEN_BUCKETS_EMPTY;
+	}
+
+	if (likely(fifo_pop(&ca->free[RESERVE_NONE], bucket)))
+		goto out;
+
+	switch (reserve) {
+	case RESERVE_ALLOC:
+		if (fifo_pop(&ca->free[RESERVE_BTREE], bucket))
+			goto out;
+		break;
+	case RESERVE_BTREE:
+		if (fifo_used(&ca->free[RESERVE_BTREE]) * 2 >=
+		    ca->free[RESERVE_BTREE].size &&
+		    fifo_pop(&ca->free[RESERVE_BTREE], bucket))
+			goto out;
+		break;
+	case RESERVE_MOVINGGC:
+		if (fifo_pop(&ca->free[RESERVE_MOVINGGC], bucket))
+			goto out;
+		break;
+	default:
+		break;
+	}
+
+	if (cl)
+		closure_wait(&c->freelist_wait, cl);
+
+	spin_unlock(&c->freelist_lock);
+
+	trace_bucket_alloc_fail(ca, reserve);
+	return FREELIST_EMPTY;
+out:
+	verify_not_on_freelist(c, ca, bucket);
+
+	ob = bch2_open_bucket_alloc(c);
+
+	spin_lock(&ob->lock);
+	buckets = bucket_array(ca);
+
+	ob->valid	= true;
+	ob->sectors_free = ca->mi.bucket_size;
+	ob->ptr		= (struct bch_extent_ptr) {
+		.gen	= buckets->b[bucket].mark.gen,
+		.offset	= bucket_to_sector(ca, bucket),
+		.dev	= ca->dev_idx,
+	};
+
+	bucket_io_clock_reset(c, ca, bucket, READ);
+	bucket_io_clock_reset(c, ca, bucket, WRITE);
+	spin_unlock(&ob->lock);
+
+	spin_unlock(&c->freelist_lock);
+
+	bch2_wake_allocator(ca);
+
+	trace_bucket_alloc(ca, reserve);
+	return ob - c->open_buckets;
+}
+
+static int __dev_alloc_cmp(struct write_point *wp,
+			   unsigned l, unsigned r)
+{
+	return ((wp->next_alloc[l] > wp->next_alloc[r]) -
+		(wp->next_alloc[l] < wp->next_alloc[r]));
+}
+
+#define dev_alloc_cmp(l, r) __dev_alloc_cmp(wp, l, r)
+
+struct dev_alloc_list bch2_wp_alloc_list(struct bch_fs *c,
+					 struct write_point *wp,
+					 struct bch_devs_mask *devs)
+{
+	struct dev_alloc_list ret = { .nr = 0 };
+	struct bch_dev *ca;
+	unsigned i;
+
+	for_each_member_device_rcu(ca, c, i, devs)
+		ret.devs[ret.nr++] = i;
+
+	bubble_sort(ret.devs, ret.nr, dev_alloc_cmp);
+	return ret;
+}
+
+void bch2_wp_rescale(struct bch_fs *c, struct bch_dev *ca,
+		     struct write_point *wp)
+{
+	u64 *v = wp->next_alloc + ca->dev_idx;
+	u64 free_space = dev_buckets_free(c, ca);
+	u64 free_space_inv = free_space
+		? div64_u64(1ULL << 48, free_space)
+		: 1ULL << 48;
+	u64 scale = *v / 4;
+
+	if (*v + free_space_inv >= *v)
+		*v += free_space_inv;
+	else
+		*v = U64_MAX;
+
+	for (v = wp->next_alloc;
+	     v < wp->next_alloc + ARRAY_SIZE(wp->next_alloc); v++)
+		*v = *v < scale ? 0 : *v - scale;
+}
+
+static enum bucket_alloc_ret bch2_bucket_alloc_set(struct bch_fs *c,
+					struct write_point *wp,
+					unsigned nr_replicas,
+					enum alloc_reserve reserve,
+					struct bch_devs_mask *devs,
+					struct closure *cl)
+{
+	enum bucket_alloc_ret ret = NO_DEVICES;
+	struct dev_alloc_list devs_sorted;
+	struct bch_dev *ca;
+	unsigned i, nr_ptrs_effective = 0;
+	bool have_cache_dev = false;
+
+	BUG_ON(nr_replicas > ARRAY_SIZE(wp->ptrs));
+
+	for (i = wp->first_ptr; i < wp->nr_ptrs; i++) {
+		ca = bch_dev_bkey_exists(c, wp->ptrs[i]->ptr.dev);
+
+		nr_ptrs_effective += ca->mi.durability;
+		have_cache_dev |= !ca->mi.durability;
+	}
+
+	if (nr_ptrs_effective >= nr_replicas)
+		return ALLOC_SUCCESS;
+
+	devs_sorted = bch2_wp_alloc_list(c, wp, devs);
+
+	for (i = 0; i < devs_sorted.nr; i++) {
+		int ob;
+
+		ca = rcu_dereference(c->devs[devs_sorted.devs[i]]);
+		if (!ca)
+			continue;
+
+		if (!ca->mi.durability &&
+		    (have_cache_dev ||
+		     wp->type != BCH_DATA_USER))
+			continue;
+
+		ob = bch2_bucket_alloc(c, ca, reserve,
+				       wp->type == BCH_DATA_USER, cl);
+		if (ob < 0) {
+			ret = ob;
+			if (ret == OPEN_BUCKETS_EMPTY)
+				break;
+			continue;
+		}
+
+		BUG_ON(ob <= 0 || ob > U8_MAX);
+		BUG_ON(wp->nr_ptrs >= ARRAY_SIZE(wp->ptrs));
+
+		wp->ptrs[wp->nr_ptrs++] = c->open_buckets + ob;
+
+		bch2_wp_rescale(c, ca, wp);
+
+		nr_ptrs_effective += ca->mi.durability;
+		have_cache_dev |= !ca->mi.durability;
+
+		__clear_bit(ca->dev_idx, devs->d);
+
+		if (nr_ptrs_effective >= nr_replicas) {
+			ret = ALLOC_SUCCESS;
+			break;
+		}
+	}
+
+	EBUG_ON(reserve == RESERVE_MOVINGGC &&
+		ret != ALLOC_SUCCESS &&
+		ret != OPEN_BUCKETS_EMPTY);
+
+	switch (ret) {
+	case ALLOC_SUCCESS:
+		return 0;
+	case NO_DEVICES:
+		return -EROFS;
+	case FREELIST_EMPTY:
+	case OPEN_BUCKETS_EMPTY:
+		return cl ? -EAGAIN : -ENOSPC;
+	default:
+		BUG();
+	}
+}
+
+/* Sector allocator */
+
+static void bch2_writepoint_drop_ptr(struct bch_fs *c,
+				     struct write_point *wp,
+				     unsigned i)
+{
+	struct open_bucket *ob = wp->ptrs[i];
+	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);
+
+	BUG_ON(ca->open_buckets_partial_nr >=
+	       ARRAY_SIZE(ca->open_buckets_partial));
+
+	if (wp->type == BCH_DATA_USER) {
+		spin_lock(&c->freelist_lock);
+		ob->on_partial_list = true;
+		ca->open_buckets_partial[ca->open_buckets_partial_nr++] =
+			ob - c->open_buckets;
+		spin_unlock(&c->freelist_lock);
+
+		closure_wake_up(&c->open_buckets_wait);
+		closure_wake_up(&c->freelist_wait);
+	} else {
+		bch2_open_bucket_put(c, ob);
+	}
+
+	array_remove_item(wp->ptrs, wp->nr_ptrs, i);
+
+	if (i < wp->first_ptr)
+		wp->first_ptr--;
+}
+
+void bch2_writepoint_drop_ptrs(struct bch_fs *c,
+			       struct write_point *wp,
+			       u16 target, bool in_target)
+{
+	int i;
+
+	for (i = wp->first_ptr - 1; i >= 0; --i)
+		if (bch2_dev_in_target(c, wp->ptrs[i]->ptr.dev,
+				       target) == in_target)
+			bch2_writepoint_drop_ptr(c, wp, i);
+}
+
+static void verify_not_stale(struct bch_fs *c, const struct write_point *wp)
+{
+#ifdef CONFIG_BCACHEFS_DEBUG
+	struct open_bucket *ob;
+	unsigned i;
+
+	writepoint_for_each_ptr_all(wp, ob, i) {
+		struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);
+
+		BUG_ON(ptr_stale(ca, &ob->ptr));
+	}
+#endif
+}
+
+static int open_bucket_add_buckets(struct bch_fs *c,
+				   u16 target,
+				   struct write_point *wp,
+				   struct bch_devs_list *devs_have,
+				   unsigned nr_replicas,
+				   enum alloc_reserve reserve,
+				   struct closure *cl)
+{
+	struct bch_devs_mask devs = c->rw_devs[wp->type];
+	const struct bch_devs_mask *t;
+	struct open_bucket *ob;
+	unsigned i;
+	int ret;
+
+	percpu_down_read(&c->usage_lock);
+	rcu_read_lock();
+
+	/* Don't allocate from devices we already have pointers to: */
+	for (i = 0; i < devs_have->nr; i++)
+		__clear_bit(devs_have->devs[i], devs.d);
+
+	writepoint_for_each_ptr_all(wp, ob, i)
+		__clear_bit(ob->ptr.dev, devs.d);
+
+	t = bch2_target_to_mask(c, target);
+	if (t)
+		bitmap_and(devs.d, devs.d, t->d, BCH_SB_MEMBERS_MAX);
+
+	ret = bch2_bucket_alloc_set(c, wp, nr_replicas, reserve, &devs, cl);
+
+	rcu_read_unlock();
+	percpu_up_read(&c->usage_lock);
+
+	return ret;
+}
+
+void bch2_writepoint_stop(struct bch_fs *c, struct bch_dev *ca,
+			  struct write_point *wp)
+{
+	struct bch_devs_mask not_self;
+
+	bitmap_complement(not_self.d, ca->self.d, BCH_SB_MEMBERS_MAX);
+
+	mutex_lock(&wp->lock);
+	wp->first_ptr = wp->nr_ptrs;
+	bch2_writepoint_drop_ptrs(c, wp, dev_to_target(ca->dev_idx), true);
+	mutex_unlock(&wp->lock);
+}
+
+static struct write_point *__writepoint_find(struct hlist_head *head,
+					     unsigned long write_point)
+{
+	struct write_point *wp;
+
+	hlist_for_each_entry_rcu(wp, head, node)
+		if (wp->write_point == write_point)
+			return wp;
+
+	return NULL;
+}
+
+static struct write_point *writepoint_find(struct bch_fs *c,
+					   unsigned long write_point)
+{
+	struct write_point *wp, *oldest;
+	struct hlist_head *head;
+
+	if (!(write_point & 1UL)) {
+		wp = (struct write_point *) write_point;
+		mutex_lock(&wp->lock);
+		return wp;
+	}
+
+	head = writepoint_hash(c, write_point);
+restart_find:
+	wp = __writepoint_find(head, write_point);
+	if (wp) {
+lock_wp:
+		mutex_lock(&wp->lock);
+		if (wp->write_point == write_point)
+			goto out;
+		mutex_unlock(&wp->lock);
+		goto restart_find;
+	}
+
+	oldest = NULL;
+	for (wp = c->write_points;
+	     wp < c->write_points + ARRAY_SIZE(c->write_points);
+	     wp++)
+		if (!oldest || time_before64(wp->last_used, oldest->last_used))
+			oldest = wp;
+
+	mutex_lock(&oldest->lock);
+	mutex_lock(&c->write_points_hash_lock);
+	wp = __writepoint_find(head, write_point);
+	if (wp && wp != oldest) {
+		mutex_unlock(&c->write_points_hash_lock);
+		mutex_unlock(&oldest->lock);
+		goto lock_wp;
+	}
+
+	wp = oldest;
+	hlist_del_rcu(&wp->node);
+	wp->write_point = write_point;
+	hlist_add_head_rcu(&wp->node, head);
+	mutex_unlock(&c->write_points_hash_lock);
+out:
+	wp->last_used = sched_clock();
+	return wp;
+}
+
+/*
+ * Get us an open_bucket we can allocate from, return with it locked:
+ */
+struct write_point *bch2_alloc_sectors_start(struct bch_fs *c,
+				unsigned target,
+				struct write_point_specifier write_point,
+				struct bch_devs_list *devs_have,
+				unsigned nr_replicas,
+				unsigned nr_replicas_required,
+				enum alloc_reserve reserve,
+				unsigned flags,
+				struct closure *cl)
+{
+	struct write_point *wp;
+	struct open_bucket *ob;
+	struct bch_dev *ca;
+	unsigned nr_ptrs_have, nr_ptrs_effective;
+	int ret, i, cache_idx = -1;
+
+	BUG_ON(!nr_replicas || !nr_replicas_required);
+
+	wp = writepoint_find(c, write_point.v);
+
+	wp->first_ptr = 0;
+
+	/* does writepoint have ptrs we can't use? */
+	writepoint_for_each_ptr(wp, ob, i)
+		if (bch2_dev_list_has_dev(*devs_have, ob->ptr.dev)) {
+			swap(wp->ptrs[i], wp->ptrs[wp->first_ptr]);
+			wp->first_ptr++;
+		}
+
+	nr_ptrs_have = wp->first_ptr;
+
+	/* does writepoint have ptrs we don't want to use? */
+	if (target)
+		writepoint_for_each_ptr(wp, ob, i)
+			if (!bch2_dev_in_target(c, ob->ptr.dev, target)) {
+				swap(wp->ptrs[i], wp->ptrs[wp->first_ptr]);
+				wp->first_ptr++;
+			}
+
+	if (flags & BCH_WRITE_ONLY_SPECIFIED_DEVS) {
+		ret = open_bucket_add_buckets(c, target, wp, devs_have,
+					      nr_replicas, reserve, cl);
+	} else {
+		ret = open_bucket_add_buckets(c, target, wp, devs_have,
+					      nr_replicas, reserve, NULL);
+		if (!ret)
+			goto alloc_done;
+
+		wp->first_ptr = nr_ptrs_have;
+
+		ret = open_bucket_add_buckets(c, 0, wp, devs_have,
+					      nr_replicas, reserve, cl);
+	}
+
+	if (ret && ret != -EROFS)
+		goto err;
+alloc_done:
+	/* check for more than one cache: */
+	for (i = wp->nr_ptrs - 1; i >= wp->first_ptr; --i) {
+		ca = bch_dev_bkey_exists(c, wp->ptrs[i]->ptr.dev);
+
+		if (ca->mi.durability)
+			continue;
+
+		/*
+		 * if we ended up with more than one cache device, prefer the
+		 * one in the target we want:
+		 */
+		if (cache_idx >= 0) {
+			if (!bch2_dev_in_target(c, wp->ptrs[i]->ptr.dev,
+						target)) {
+				bch2_writepoint_drop_ptr(c, wp, i);
+			} else {
+				bch2_writepoint_drop_ptr(c, wp, cache_idx);
+				cache_idx = i;
+			}
+		} else {
+			cache_idx = i;
+		}
+	}
+
+	/* we might have more effective replicas than required: */
+	nr_ptrs_effective = 0;
+	writepoint_for_each_ptr(wp, ob, i) {
+		ca = bch_dev_bkey_exists(c, ob->ptr.dev);
+		nr_ptrs_effective += ca->mi.durability;
+	}
+
+	if (ret == -EROFS &&
+	    nr_ptrs_effective >= nr_replicas_required)
+		ret = 0;
+
+	if (ret)
+		goto err;
+
+	if (nr_ptrs_effective > nr_replicas) {
+		writepoint_for_each_ptr(wp, ob, i) {
+			ca = bch_dev_bkey_exists(c, ob->ptr.dev);
+
+			if (ca->mi.durability &&
+			    ca->mi.durability <= nr_ptrs_effective - nr_replicas &&
+			    !bch2_dev_in_target(c, ob->ptr.dev, target)) {
+				swap(wp->ptrs[i], wp->ptrs[wp->first_ptr]);
+				wp->first_ptr++;
+				nr_ptrs_effective -= ca->mi.durability;
+			}
+		}
+	}
+
+	if (nr_ptrs_effective > nr_replicas) {
+		writepoint_for_each_ptr(wp, ob, i) {
+			ca = bch_dev_bkey_exists(c, ob->ptr.dev);
+
+			if (ca->mi.durability &&
+			    ca->mi.durability <= nr_ptrs_effective - nr_replicas) {
+				swap(wp->ptrs[i], wp->ptrs[wp->first_ptr]);
+				wp->first_ptr++;
+				nr_ptrs_effective -= ca->mi.durability;
+			}
+		}
+	}
+
+	/* Remove pointers we don't want to use: */
+	if (target)
+		bch2_writepoint_drop_ptrs(c, wp, target, false);
+
+	BUG_ON(wp->first_ptr >= wp->nr_ptrs);
+	BUG_ON(nr_ptrs_effective < nr_replicas_required);
+
+	wp->sectors_free = UINT_MAX;
+
+	writepoint_for_each_ptr(wp, ob, i)
+		wp->sectors_free = min(wp->sectors_free, ob->sectors_free);
+
+	BUG_ON(!wp->sectors_free || wp->sectors_free == UINT_MAX);
+
+	verify_not_stale(c, wp);
+
+	return wp;
+err:
+	mutex_unlock(&wp->lock);
+	return ERR_PTR(ret);
+}
+
+/*
+ * Append pointers to the space we just allocated to @k, and mark @sectors space
+ * as allocated out of @ob
+ */
+void bch2_alloc_sectors_append_ptrs(struct bch_fs *c, struct write_point *wp,
+				    struct bkey_i_extent *e, unsigned sectors)
+{
+	struct open_bucket *ob;
+	unsigned i;
+
+	BUG_ON(sectors > wp->sectors_free);
+	wp->sectors_free -= sectors;
+
+	writepoint_for_each_ptr(wp, ob, i) {
+		struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);
+		struct bch_extent_ptr tmp = ob->ptr;
+
+		EBUG_ON(bch2_extent_has_device(extent_i_to_s_c(e), ob->ptr.dev));
+
+		tmp.cached = bkey_extent_is_cached(&e->k) ||
+			(!ca->mi.durability && wp->type == BCH_DATA_USER);
+
+		tmp.offset += ca->mi.bucket_size - ob->sectors_free;
+		extent_ptr_append(e, tmp);
+
+		BUG_ON(sectors > ob->sectors_free);
+		ob->sectors_free -= sectors;
+	}
+}
+
+/*
+ * Append pointers to the space we just allocated to @k, and mark @sectors space
+ * as allocated out of @ob
+ */
+void bch2_alloc_sectors_done(struct bch_fs *c, struct write_point *wp)
+{
+	int i;
+
+	for (i = wp->nr_ptrs - 1; i >= 0; --i) {
+		struct open_bucket *ob = wp->ptrs[i];
+
+		if (!ob->sectors_free) {
+			array_remove_item(wp->ptrs, wp->nr_ptrs, i);
+			bch2_open_bucket_put(c, ob);
+		}
+	}
+
+	mutex_unlock(&wp->lock);
+}
diff --git a/fs/bcachefs/alloc.h b/fs/bcachefs/alloc_foreground.h
index 739df233236c..1c738e4ba6c9 100644
--- a/fs/bcachefs/alloc.h
+++ b/fs/bcachefs/alloc_foreground.h
@@ -1,5 +1,6 @@
-#ifndef _BCACHEFS_ALLOC_H
-#define _BCACHEFS_ALLOC_H
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_ALLOC_FOREGROUND_H
+#define _BCACHEFS_ALLOC_FOREGROUND_H
 
 #include "bcachefs.h"
 #include "alloc_types.h"
@@ -9,16 +10,6 @@ struct bch_dev;
 struct bch_fs;
 struct bch_devs_List;
 
-#define ALLOC_SCAN_BATCH(ca)		((ca)->mi.nbuckets >> 9)
-
-const char *bch2_alloc_invalid(const struct bch_fs *, struct bkey_s_c);
-int bch2_alloc_to_text(struct bch_fs *, char *, size_t, struct bkey_s_c);
-
-#define bch2_bkey_alloc_ops (struct bkey_ops) {		\
-	.key_invalid	= bch2_alloc_invalid,		\
-	.val_to_text	= bch2_alloc_to_text,		\
-}
-
 struct dev_alloc_list {
 	unsigned	nr;
 	u8		devs[BCH_SB_MEMBERS_MAX];
@@ -30,16 +21,6 @@ struct dev_alloc_list bch2_wp_alloc_list(struct bch_fs *,
 void bch2_wp_rescale(struct bch_fs *, struct bch_dev *,
 		     struct write_point *);
 
-int bch2_alloc_read(struct bch_fs *, struct list_head *);
-int bch2_alloc_replay_key(struct bch_fs *, struct bpos);
-
-enum bucket_alloc_ret {
-	ALLOC_SUCCESS		= 0,
-	OPEN_BUCKETS_EMPTY	= -1,
-	FREELIST_EMPTY		= -2,	/* Allocator thread not keeping up */
-	NO_DEVICES		= -3,	/* -EROFS */
-};
-
 long bch2_bucket_alloc_new_fs(struct bch_dev *);
 
 int bch2_bucket_alloc(struct bch_fs *, struct bch_dev *, enum alloc_reserve, bool,
@@ -100,15 +81,19 @@ void bch2_alloc_sectors_append_ptrs(struct bch_fs *, struct write_point *,
 				    struct bkey_i_extent *, unsigned);
 void bch2_alloc_sectors_done(struct bch_fs *, struct write_point *);
 
-static inline void bch2_wake_allocator(struct bch_dev *ca)
+void bch2_writepoint_stop(struct bch_fs *, struct bch_dev *,
+			  struct write_point *);
+
+void bch2_writepoint_drop_ptrs(struct bch_fs *, struct write_point *,
+			       u16, bool);
+
+static inline struct hlist_head *writepoint_hash(struct bch_fs *c,
+						 unsigned long write_point)
 {
-	struct task_struct *p;
+	unsigned hash =
+		hash_long(write_point, ilog2(ARRAY_SIZE(c->write_points_hash)));
 
-	rcu_read_lock();
-	p = rcu_dereference(ca->alloc_thread);
-	if (p)
-		wake_up_process(p);
-	rcu_read_unlock();
+	return &c->write_points_hash[hash];
 }
 
 static inline struct write_point_specifier writepoint_hashed(unsigned long v)
@@ -121,14 +106,6 @@ static inline struct write_point_specifier writepoint_ptr(struct write_point *wp
 	return (struct write_point_specifier) { .v = (unsigned long) wp };
 }
 
-void bch2_recalc_capacity(struct bch_fs *);
-
-void bch2_dev_allocator_remove(struct bch_fs *, struct bch_dev *);
-void bch2_dev_allocator_add(struct bch_fs *, struct bch_dev *);
-
-void bch2_dev_allocator_stop(struct bch_dev *);
-int bch2_dev_allocator_start(struct bch_dev *);
-
 static inline void writepoint_init(struct write_point *wp,
 				   enum bch_data_type type)
 {
@@ -136,8 +113,4 @@ static inline void writepoint_init(struct write_point *wp,
 	wp->type = type;
 }
 
-int bch2_alloc_write(struct bch_fs *);
-int bch2_fs_allocator_start(struct bch_fs *);
-void bch2_fs_allocator_init(struct bch_fs *);
-
-#endif /* _BCACHEFS_ALLOC_H */
+#endif /* _BCACHEFS_ALLOC_FOREGROUND_H */
diff --git a/fs/bcachefs/bkey_methods.c b/fs/bcachefs/bkey_methods.c
index 8c6c2ca3c992..b3f5f28b8761 100644
--- a/fs/bcachefs/bkey_methods.c
+++ b/fs/bcachefs/bkey_methods.c
@@ -3,7 +3,7 @@
 #include "bcachefs.h"
 #include "bkey_methods.h"
 #include "btree_types.h"
-#include "alloc.h"
+#include "alloc_background.h"
 #include "dirent.h"
 #include "error.h"
 #include "extents.h"
diff --git a/fs/bcachefs/btree_gc.c b/fs/bcachefs/btree_gc.c
index 5b1e1aab36e9..7fd75435542b 100644
--- a/fs/bcachefs/btree_gc.c
+++ b/fs/bcachefs/btree_gc.c
@@ -5,7 +5,7 @@
  */
 
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_background.h"
 #include "bkey_methods.h"
 #include "btree_locking.h"
 #include "btree_update_interior.h"
diff --git a/fs/bcachefs/btree_update_interior.c b/fs/bcachefs/btree_update_interior.c
index 6d99f3d191d3..0ca998035bab 100644
--- a/fs/bcachefs/btree_update_interior.c
+++ b/fs/bcachefs/btree_update_interior.c
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_foreground.h"
 #include "bkey_methods.h"
 #include "btree_cache.h"
 #include "btree_gc.h"
diff --git a/fs/bcachefs/buckets.c b/fs/bcachefs/buckets.c
index ab61abdf975d..c6544f35eb09 100644
--- a/fs/bcachefs/buckets.c
+++ b/fs/bcachefs/buckets.c
@@ -64,7 +64,7 @@
  */
 
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_background.h"
 #include "btree_gc.h"
 #include "buckets.h"
 #include "error.h"
diff --git a/fs/bcachefs/chardev.c b/fs/bcachefs/chardev.c
index db0f990bebf4..d24cff52ba96 100644
--- a/fs/bcachefs/chardev.c
+++ b/fs/bcachefs/chardev.c
@@ -2,7 +2,6 @@
 #ifndef NO_BCACHEFS_CHARDEV
 
 #include "bcachefs.h"
-#include "alloc.h"
 #include "bcachefs_ioctl.h"
 #include "buckets.h"
 #include "chardev.h"
diff --git a/fs/bcachefs/fs-io.c b/fs/bcachefs/fs-io.c
index 195af78cb474..2902e5f925ef 100644
--- a/fs/bcachefs/fs-io.c
+++ b/fs/bcachefs/fs-io.c
@@ -2,6 +2,7 @@
 #ifndef NO_BCACHEFS_FS
 
 #include "bcachefs.h"
+#include "alloc_foreground.h"
 #include "btree_update.h"
 #include "buckets.h"
 #include "clock.h"
diff --git a/fs/bcachefs/io.c b/fs/bcachefs/io.c
index 50cc87b7875d..dfd2d3b708c5 100644
--- a/fs/bcachefs/io.c
+++ b/fs/bcachefs/io.c
@@ -7,7 +7,7 @@
  */
 
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_foreground.h"
 #include "bset.h"
 #include "btree_update.h"
 #include "buckets.h"
diff --git a/fs/bcachefs/io.h b/fs/bcachefs/io.h
index f814226a5196..62f5861005ea 100644
--- a/fs/bcachefs/io.h
+++ b/fs/bcachefs/io.h
@@ -2,7 +2,6 @@
 #ifndef _BCACHEFS_IO_H
 #define _BCACHEFS_IO_H
 
-#include "alloc.h"
 #include "checksum.h"
 #include "io_types.h"
 
diff --git a/fs/bcachefs/journal.c b/fs/bcachefs/journal.c
index b83548ae33b2..97fbc2698dc0 100644
--- a/fs/bcachefs/journal.c
+++ b/fs/bcachefs/journal.c
@@ -6,7 +6,7 @@
  */
 
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_foreground.h"
 #include "bkey_methods.h"
 #include "btree_gc.h"
 #include "buckets.h"
diff --git a/fs/bcachefs/journal_io.c b/fs/bcachefs/journal_io.c
index 16ea32dc1fa4..9dd881c0410e 100644
--- a/fs/bcachefs/journal_io.c
+++ b/fs/bcachefs/journal_io.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_background.h"
+#include "alloc_foreground.h"
 #include "btree_gc.h"
 #include "btree_update.h"
 #include "buckets.h"
diff --git a/fs/bcachefs/move.c b/fs/bcachefs/move.c
index 9402b45bf868..96f04f349fb1 100644
--- a/fs/bcachefs/move.c
+++ b/fs/bcachefs/move.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
+#include "alloc_foreground.h"
 #include "btree_gc.h"
 #include "btree_update.h"
 #include "buckets.h"
diff --git a/fs/bcachefs/movinggc.c b/fs/bcachefs/movinggc.c
index 26b8e95db1db..b7def19bdd85 100644
--- a/fs/bcachefs/movinggc.c
+++ b/fs/bcachefs/movinggc.c
@@ -6,6 +6,7 @@
  */
 
 #include "bcachefs.h"
+#include "alloc_foreground.h"
 #include "btree_iter.h"
 #include "btree_update.h"
 #include "buckets.h"
diff --git a/fs/bcachefs/rebalance.c b/fs/bcachefs/rebalance.c
index 74702e753f60..461af44dbde7 100644
--- a/fs/bcachefs/rebalance.c
+++ b/fs/bcachefs/rebalance.c
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_foreground.h"
 #include "btree_iter.h"
 #include "buckets.h"
 #include "clock.h"
diff --git a/fs/bcachefs/recovery.c b/fs/bcachefs/recovery.c
index 3deb59a675e1..6d603654d150 100644
--- a/fs/bcachefs/recovery.c
+++ b/fs/bcachefs/recovery.c
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_background.h"
 #include "btree_gc.h"
 #include "btree_update.h"
 #include "btree_update_interior.h"
diff --git a/fs/bcachefs/super.c b/fs/bcachefs/super.c
index ffeffd50b083..9d9d4fb8348b 100644
--- a/fs/bcachefs/super.c
+++ b/fs/bcachefs/super.c
@@ -8,7 +8,8 @@
  */
 
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_background.h"
+#include "alloc_foreground.h"
 #include "btree_cache.h"
 #include "btree_gc.h"
 #include "btree_update_interior.h"
diff --git a/fs/bcachefs/sysfs.c b/fs/bcachefs/sysfs.c
index a472e454099b..b7a65bc20430 100644
--- a/fs/bcachefs/sysfs.c
+++ b/fs/bcachefs/sysfs.c
@@ -9,7 +9,7 @@
 #ifndef NO_BCACHEFS_SYSFS
 
 #include "bcachefs.h"
-#include "alloc.h"
+#include "alloc_background.h"
 #include "compress.h"
 #include "sysfs.h"
 #include "btree_cache.h"