1 // SPDX-License-Identifier: GPL-2.0
3 * bcache journalling code, for btree insertions
5 * Copyright 2012 Google, Inc.
13 #include <trace/events/bcache.h>
16 * Journal replay/recovery:
18 * This code is all driven from run_cache_set(); we first read the journal
19 * entries, do some other stuff, then we mark all the keys in the journal
20 * entries (same as garbage collection would), then we replay them - reinserting
21 * them into the cache in precisely the same order as they appear in the
24 * We only journal keys that go in leaf nodes, which simplifies things quite a
28 static void journal_read_endio(struct bio *bio)
30 struct closure *cl = bio->bi_private;
35 static int journal_read_bucket(struct cache *ca, struct list_head *list,
36 unsigned int bucket_index)
38 struct journal_device *ja = &ca->journal;
39 struct bio *bio = &ja->bio;
41 struct journal_replay *i;
42 struct jset *j, *data = ca->set->journal.w[0].data;
44 unsigned int len, left, offset = 0;
46 sector_t bucket = bucket_to_sector(ca->set, ca->sb.d[bucket_index]);
48 closure_init_stack(&cl);
50 pr_debug("reading %u", bucket_index);
52 while (offset < ca->sb.bucket_size) {
53 reread: left = ca->sb.bucket_size - offset;
54 len = min_t(unsigned int, left, PAGE_SECTORS << JSET_BITS);
57 bio->bi_iter.bi_sector = bucket + offset;
58 bio_set_dev(bio, ca->bdev);
59 bio->bi_iter.bi_size = len << 9;
61 bio->bi_end_io = journal_read_endio;
62 bio->bi_private = &cl;
63 bio_set_op_attrs(bio, REQ_OP_READ, 0);
64 bch_bio_map(bio, data);
66 closure_bio_submit(ca->set, bio, &cl);
69 /* This function could be simpler now since we no longer write
70 * journal entries that overlap bucket boundaries; this means
71 * the start of a bucket will always have a valid journal entry
72 * if it has any journal entries at all.
77 struct list_head *where;
78 size_t blocks, bytes = set_bytes(j);
80 if (j->magic != jset_magic(&ca->sb)) {
81 pr_debug("%u: bad magic", bucket_index);
85 if (bytes > left << 9 ||
86 bytes > PAGE_SIZE << JSET_BITS) {
87 pr_info("%u: too big, %zu bytes, offset %u",
88 bucket_index, bytes, offset);
95 if (j->csum != csum_set(j)) {
96 pr_info("%u: bad csum, %zu bytes, offset %u",
97 bucket_index, bytes, offset);
101 blocks = set_blocks(j, block_bytes(ca->set));
104 * Nodes in 'list' are in linear increasing order of
105 * i->j.seq, the node on head has the smallest (oldest)
106 * journal seq, the node on tail has the biggest
107 * (latest) journal seq.
111 * Check from the oldest jset for last_seq. If
112 * i->j.seq < j->last_seq, it means the oldest jset
113 * in list is expired and useless, remove it from
114 * this list. Otherwise, j is a condidate jset for
115 * further following checks.
117 while (!list_empty(list)) {
118 i = list_first_entry(list,
119 struct journal_replay, list);
120 if (i->j.seq >= j->last_seq)
126 /* iterate list in reverse order (from latest jset) */
127 list_for_each_entry_reverse(i, list, list) {
128 if (j->seq == i->j.seq)
132 * if j->seq is less than any i->j.last_seq
133 * in list, j is an expired and useless jset.
135 if (j->seq < i->j.last_seq)
139 * 'where' points to first jset in list which
142 if (j->seq > i->j.seq) {
150 i = kmalloc(offsetof(struct journal_replay, j) +
154 memcpy(&i->j, j, bytes);
155 /* Add to the location after 'where' points to */
156 list_add(&i->list, where);
159 if (j->seq > ja->seq[bucket_index])
160 ja->seq[bucket_index] = j->seq;
162 offset += blocks * ca->sb.block_size;
163 len -= blocks * ca->sb.block_size;
164 j = ((void *) j) + blocks * block_bytes(ca);
171 int bch_journal_read(struct cache_set *c, struct list_head *list)
173 #define read_bucket(b) \
175 ret = journal_read_bucket(ca, list, b); \
176 __set_bit(b, bitmap); \
186 for_each_cache(ca, c, iter) {
187 struct journal_device *ja = &ca->journal;
188 DECLARE_BITMAP(bitmap, SB_JOURNAL_BUCKETS);
189 unsigned int i, l, r, m;
192 bitmap_zero(bitmap, SB_JOURNAL_BUCKETS);
193 pr_debug("%u journal buckets", ca->sb.njournal_buckets);
196 * Read journal buckets ordered by golden ratio hash to quickly
197 * find a sequence of buckets with valid journal entries
199 for (i = 0; i < ca->sb.njournal_buckets; i++) {
201 * We must try the index l with ZERO first for
202 * correctness due to the scenario that the journal
203 * bucket is circular buffer which might have wrapped
205 l = (i * 2654435769U) % ca->sb.njournal_buckets;
207 if (test_bit(l, bitmap))
215 * If that fails, check all the buckets we haven't checked
218 pr_debug("falling back to linear search");
220 for (l = find_first_zero_bit(bitmap, ca->sb.njournal_buckets);
221 l < ca->sb.njournal_buckets;
222 l = find_next_zero_bit(bitmap, ca->sb.njournal_buckets,
227 /* no journal entries on this device? */
228 if (l == ca->sb.njournal_buckets)
231 BUG_ON(list_empty(list));
235 r = find_next_bit(bitmap, ca->sb.njournal_buckets, l + 1);
236 pr_debug("starting binary search, l %u r %u", l, r);
239 seq = list_entry(list->prev, struct journal_replay,
245 if (seq != list_entry(list->prev, struct journal_replay,
253 * Read buckets in reverse order until we stop finding more
256 pr_debug("finishing up: m %u njournal_buckets %u",
257 m, ca->sb.njournal_buckets);
262 l = ca->sb.njournal_buckets - 1;
267 if (test_bit(l, bitmap))
276 for (i = 0; i < ca->sb.njournal_buckets; i++)
277 if (ja->seq[i] > seq) {
280 * When journal_reclaim() goes to allocate for
281 * the first time, it'll use the bucket after
285 ja->last_idx = ja->discard_idx = (i + 1) %
286 ca->sb.njournal_buckets;
291 if (!list_empty(list))
292 c->journal.seq = list_entry(list->prev,
293 struct journal_replay,
300 void bch_journal_mark(struct cache_set *c, struct list_head *list)
304 struct journal_replay *i;
305 struct journal *j = &c->journal;
306 uint64_t last = j->seq;
309 * journal.pin should never fill up - we never write a journal
310 * entry when it would fill up. But if for some reason it does, we
311 * iterate over the list in reverse order so that we can just skip that
312 * refcount instead of bugging.
315 list_for_each_entry_reverse(i, list, list) {
316 BUG_ON(last < i->j.seq);
319 while (last-- != i->j.seq)
320 if (fifo_free(&j->pin) > 1) {
321 fifo_push_front(&j->pin, p);
322 atomic_set(&fifo_front(&j->pin), 0);
325 if (fifo_free(&j->pin) > 1) {
326 fifo_push_front(&j->pin, p);
327 i->pin = &fifo_front(&j->pin);
328 atomic_set(i->pin, 1);
332 k < bset_bkey_last(&i->j);
334 if (!__bch_extent_invalid(c, k)) {
337 for (j = 0; j < KEY_PTRS(k); j++)
338 if (ptr_available(c, k, j))
339 atomic_inc(&PTR_BUCKET(c, k, j)->pin);
341 bch_initial_mark_key(c, 0, k);
346 static bool is_discard_enabled(struct cache_set *s)
351 for_each_cache(ca, s, i)
358 int bch_journal_replay(struct cache_set *s, struct list_head *list)
360 int ret = 0, keys = 0, entries = 0;
362 struct journal_replay *i =
363 list_entry(list->prev, struct journal_replay, list);
365 uint64_t start = i->j.last_seq, end = i->j.seq, n = start;
366 struct keylist keylist;
368 list_for_each_entry(i, list, list) {
369 BUG_ON(i->pin && atomic_read(i->pin) != 1);
372 if (n == start && is_discard_enabled(s))
373 pr_info("bcache: journal entries %llu-%llu may be discarded! (replaying %llu-%llu)",
374 n, i->j.seq - 1, start, end);
376 pr_err("bcache: journal entries %llu-%llu missing! (replaying %llu-%llu)",
377 n, i->j.seq - 1, start, end);
384 k < bset_bkey_last(&i->j);
386 trace_bcache_journal_replay_key(k);
388 bch_keylist_init_single(&keylist, k);
390 ret = bch_btree_insert(s, &keylist, i->pin, NULL);
394 BUG_ON(!bch_keylist_empty(&keylist));
406 pr_info("journal replay done, %i keys in %i entries, seq %llu",
409 while (!list_empty(list)) {
410 i = list_first_entry(list, struct journal_replay, list);
420 static void btree_flush_write(struct cache_set *c)
422 struct btree *b, *t, *btree_nodes[BTREE_FLUSH_NR];
425 atomic_t *fifo_front_p, *now_fifo_front_p;
428 if (c->journal.btree_flushing)
431 spin_lock(&c->journal.flush_write_lock);
432 if (c->journal.btree_flushing) {
433 spin_unlock(&c->journal.flush_write_lock);
436 c->journal.btree_flushing = true;
437 spin_unlock(&c->journal.flush_write_lock);
439 /* get the oldest journal entry and check its refcount */
440 spin_lock(&c->journal.lock);
441 fifo_front_p = &fifo_front(&c->journal.pin);
442 ref_nr = atomic_read(fifo_front_p);
445 * do nothing if no btree node references
446 * the oldest journal entry
448 spin_unlock(&c->journal.lock);
451 spin_unlock(&c->journal.lock);
453 mask = c->journal.pin.mask;
455 atomic_long_inc(&c->flush_write);
456 memset(btree_nodes, 0, sizeof(btree_nodes));
458 mutex_lock(&c->bucket_lock);
459 list_for_each_entry_safe_reverse(b, t, &c->btree_cache, list) {
461 * It is safe to get now_fifo_front_p without holding
462 * c->journal.lock here, because we don't need to know
463 * the exactly accurate value, just check whether the
464 * front pointer of c->journal.pin is changed.
466 now_fifo_front_p = &fifo_front(&c->journal.pin);
468 * If the oldest journal entry is reclaimed and front
469 * pointer of c->journal.pin changes, it is unnecessary
470 * to scan c->btree_cache anymore, just quit the loop and
471 * flush out what we have already.
473 if (now_fifo_front_p != fifo_front_p)
476 * quit this loop if all matching btree nodes are
477 * scanned and record in btree_nodes[] already.
479 ref_nr = atomic_read(fifo_front_p);
483 if (btree_node_journal_flush(b))
484 pr_err("BUG: flush_write bit should not be set here!");
486 mutex_lock(&b->write_lock);
488 if (!btree_node_dirty(b)) {
489 mutex_unlock(&b->write_lock);
493 if (!btree_current_write(b)->journal) {
494 mutex_unlock(&b->write_lock);
499 * Only select the btree node which exactly references
500 * the oldest journal entry.
502 * If the journal entry pointed by fifo_front_p is
503 * reclaimed in parallel, don't worry:
504 * - the list_for_each_xxx loop will quit when checking
505 * next now_fifo_front_p.
506 * - If there are matched nodes recorded in btree_nodes[],
507 * they are clean now (this is why and how the oldest
508 * journal entry can be reclaimed). These selected nodes
509 * will be ignored and skipped in the folowing for-loop.
511 if (((btree_current_write(b)->journal - fifo_front_p) &
513 mutex_unlock(&b->write_lock);
517 set_btree_node_journal_flush(b);
519 mutex_unlock(&b->write_lock);
521 btree_nodes[nr++] = b;
523 * To avoid holding c->bucket_lock too long time,
524 * only scan for BTREE_FLUSH_NR matched btree nodes
525 * at most. If there are more btree nodes reference
526 * the oldest journal entry, try to flush them next
527 * time when btree_flush_write() is called.
529 if (nr == BTREE_FLUSH_NR)
532 mutex_unlock(&c->bucket_lock);
534 for (i = 0; i < nr; i++) {
537 pr_err("BUG: btree_nodes[%d] is NULL", i);
541 /* safe to check without holding b->write_lock */
542 if (!btree_node_journal_flush(b)) {
543 pr_err("BUG: bnode %p: journal_flush bit cleaned", b);
547 mutex_lock(&b->write_lock);
548 if (!btree_current_write(b)->journal) {
549 clear_bit(BTREE_NODE_journal_flush, &b->flags);
550 mutex_unlock(&b->write_lock);
551 pr_debug("bnode %p: written by others", b);
555 if (!btree_node_dirty(b)) {
556 clear_bit(BTREE_NODE_journal_flush, &b->flags);
557 mutex_unlock(&b->write_lock);
558 pr_debug("bnode %p: dirty bit cleaned by others", b);
562 __bch_btree_node_write(b, NULL);
563 clear_bit(BTREE_NODE_journal_flush, &b->flags);
564 mutex_unlock(&b->write_lock);
568 spin_lock(&c->journal.flush_write_lock);
569 c->journal.btree_flushing = false;
570 spin_unlock(&c->journal.flush_write_lock);
573 #define last_seq(j) ((j)->seq - fifo_used(&(j)->pin) + 1)
575 static void journal_discard_endio(struct bio *bio)
577 struct journal_device *ja =
578 container_of(bio, struct journal_device, discard_bio);
579 struct cache *ca = container_of(ja, struct cache, journal);
581 atomic_set(&ja->discard_in_flight, DISCARD_DONE);
583 closure_wake_up(&ca->set->journal.wait);
584 closure_put(&ca->set->cl);
587 static void journal_discard_work(struct work_struct *work)
589 struct journal_device *ja =
590 container_of(work, struct journal_device, discard_work);
592 submit_bio(&ja->discard_bio);
595 static void do_journal_discard(struct cache *ca)
597 struct journal_device *ja = &ca->journal;
598 struct bio *bio = &ja->discard_bio;
601 ja->discard_idx = ja->last_idx;
605 switch (atomic_read(&ja->discard_in_flight)) {
606 case DISCARD_IN_FLIGHT:
610 ja->discard_idx = (ja->discard_idx + 1) %
611 ca->sb.njournal_buckets;
613 atomic_set(&ja->discard_in_flight, DISCARD_READY);
617 if (ja->discard_idx == ja->last_idx)
620 atomic_set(&ja->discard_in_flight, DISCARD_IN_FLIGHT);
622 bio_init(bio, bio->bi_inline_vecs, 1);
623 bio_set_op_attrs(bio, REQ_OP_DISCARD, 0);
624 bio->bi_iter.bi_sector = bucket_to_sector(ca->set,
625 ca->sb.d[ja->discard_idx]);
626 bio_set_dev(bio, ca->bdev);
627 bio->bi_iter.bi_size = bucket_bytes(ca);
628 bio->bi_end_io = journal_discard_endio;
630 closure_get(&ca->set->cl);
631 INIT_WORK(&ja->discard_work, journal_discard_work);
632 queue_work(bch_journal_wq, &ja->discard_work);
636 static void journal_reclaim(struct cache_set *c)
638 struct bkey *k = &c->journal.key;
641 unsigned int iter, n = 0;
642 atomic_t p __maybe_unused;
644 atomic_long_inc(&c->reclaim);
646 while (!atomic_read(&fifo_front(&c->journal.pin)))
647 fifo_pop(&c->journal.pin, p);
649 last_seq = last_seq(&c->journal);
651 /* Update last_idx */
653 for_each_cache(ca, c, iter) {
654 struct journal_device *ja = &ca->journal;
656 while (ja->last_idx != ja->cur_idx &&
657 ja->seq[ja->last_idx] < last_seq)
658 ja->last_idx = (ja->last_idx + 1) %
659 ca->sb.njournal_buckets;
662 for_each_cache(ca, c, iter)
663 do_journal_discard(ca);
665 if (c->journal.blocks_free)
670 * XXX: Sort by free journal space
673 for_each_cache(ca, c, iter) {
674 struct journal_device *ja = &ca->journal;
675 unsigned int next = (ja->cur_idx + 1) % ca->sb.njournal_buckets;
677 /* No space available on this device */
678 if (next == ja->discard_idx)
682 k->ptr[n++] = MAKE_PTR(0,
683 bucket_to_sector(c, ca->sb.d[ja->cur_idx]),
685 atomic_long_inc(&c->reclaimed_journal_buckets);
691 c->journal.blocks_free = c->sb.bucket_size >> c->block_bits;
694 if (!journal_full(&c->journal))
695 __closure_wake_up(&c->journal.wait);
698 void bch_journal_next(struct journal *j)
702 j->cur = (j->cur == j->w)
707 * The fifo_push() needs to happen at the same time as j->seq is
708 * incremented for last_seq() to be calculated correctly
710 BUG_ON(!fifo_push(&j->pin, p));
711 atomic_set(&fifo_back(&j->pin), 1);
713 j->cur->data->seq = ++j->seq;
714 j->cur->dirty = false;
715 j->cur->need_write = false;
716 j->cur->data->keys = 0;
718 if (fifo_full(&j->pin))
719 pr_debug("journal_pin full (%zu)", fifo_used(&j->pin));
722 static void journal_write_endio(struct bio *bio)
724 struct journal_write *w = bio->bi_private;
726 cache_set_err_on(bio->bi_status, w->c, "journal io error");
727 closure_put(&w->c->journal.io);
730 static void journal_write(struct closure *cl);
732 static void journal_write_done(struct closure *cl)
734 struct journal *j = container_of(cl, struct journal, io);
735 struct journal_write *w = (j->cur == j->w)
739 __closure_wake_up(&w->wait);
740 continue_at_nobarrier(cl, journal_write, bch_journal_wq);
743 static void journal_write_unlock(struct closure *cl)
744 __releases(&c->journal.lock)
746 struct cache_set *c = container_of(cl, struct cache_set, journal.io);
748 c->journal.io_in_flight = 0;
749 spin_unlock(&c->journal.lock);
752 static void journal_write_unlocked(struct closure *cl)
753 __releases(c->journal.lock)
755 struct cache_set *c = container_of(cl, struct cache_set, journal.io);
757 struct journal_write *w = c->journal.cur;
758 struct bkey *k = &c->journal.key;
759 unsigned int i, sectors = set_blocks(w->data, block_bytes(c)) *
763 struct bio_list list;
765 bio_list_init(&list);
767 if (!w->need_write) {
768 closure_return_with_destructor(cl, journal_write_unlock);
770 } else if (journal_full(&c->journal)) {
772 spin_unlock(&c->journal.lock);
774 btree_flush_write(c);
775 continue_at(cl, journal_write, bch_journal_wq);
779 c->journal.blocks_free -= set_blocks(w->data, block_bytes(c));
781 w->data->btree_level = c->root->level;
783 bkey_copy(&w->data->btree_root, &c->root->key);
784 bkey_copy(&w->data->uuid_bucket, &c->uuid_bucket);
786 for_each_cache(ca, c, i)
787 w->data->prio_bucket[ca->sb.nr_this_dev] = ca->prio_buckets[0];
789 w->data->magic = jset_magic(&c->sb);
790 w->data->version = BCACHE_JSET_VERSION;
791 w->data->last_seq = last_seq(&c->journal);
792 w->data->csum = csum_set(w->data);
794 for (i = 0; i < KEY_PTRS(k); i++) {
795 ca = PTR_CACHE(c, k, i);
796 bio = &ca->journal.bio;
798 atomic_long_add(sectors, &ca->meta_sectors_written);
801 bio->bi_iter.bi_sector = PTR_OFFSET(k, i);
802 bio_set_dev(bio, ca->bdev);
803 bio->bi_iter.bi_size = sectors << 9;
805 bio->bi_end_io = journal_write_endio;
807 bio_set_op_attrs(bio, REQ_OP_WRITE,
808 REQ_SYNC|REQ_META|REQ_PREFLUSH|REQ_FUA);
809 bch_bio_map(bio, w->data);
811 trace_bcache_journal_write(bio, w->data->keys);
812 bio_list_add(&list, bio);
814 SET_PTR_OFFSET(k, i, PTR_OFFSET(k, i) + sectors);
816 ca->journal.seq[ca->journal.cur_idx] = w->data->seq;
819 /* If KEY_PTRS(k) == 0, this jset gets lost in air */
822 atomic_dec_bug(&fifo_back(&c->journal.pin));
823 bch_journal_next(&c->journal);
826 spin_unlock(&c->journal.lock);
828 while ((bio = bio_list_pop(&list)))
829 closure_bio_submit(c, bio, cl);
831 continue_at(cl, journal_write_done, NULL);
834 static void journal_write(struct closure *cl)
836 struct cache_set *c = container_of(cl, struct cache_set, journal.io);
838 spin_lock(&c->journal.lock);
839 journal_write_unlocked(cl);
842 static void journal_try_write(struct cache_set *c)
843 __releases(c->journal.lock)
845 struct closure *cl = &c->journal.io;
846 struct journal_write *w = c->journal.cur;
848 w->need_write = true;
850 if (!c->journal.io_in_flight) {
851 c->journal.io_in_flight = 1;
852 closure_call(cl, journal_write_unlocked, NULL, &c->cl);
854 spin_unlock(&c->journal.lock);
858 static struct journal_write *journal_wait_for_write(struct cache_set *c,
860 __acquires(&c->journal.lock)
866 closure_init_stack(&cl);
868 spin_lock(&c->journal.lock);
871 struct journal_write *w = c->journal.cur;
873 sectors = __set_blocks(w->data, w->data->keys + nkeys,
874 block_bytes(c)) * c->sb.block_size;
876 if (sectors <= min_t(size_t,
877 c->journal.blocks_free * c->sb.block_size,
878 PAGE_SECTORS << JSET_BITS))
882 closure_wait(&c->journal.wait, &cl);
884 if (!journal_full(&c->journal)) {
886 trace_bcache_journal_entry_full(c);
889 * XXX: If we were inserting so many keys that they
890 * won't fit in an _empty_ journal write, we'll
891 * deadlock. For now, handle this in
892 * bch_keylist_realloc() - but something to think about.
894 BUG_ON(!w->data->keys);
896 journal_try_write(c); /* unlocks */
899 trace_bcache_journal_full(c);
902 spin_unlock(&c->journal.lock);
904 btree_flush_write(c);
908 spin_lock(&c->journal.lock);
913 static void journal_write_work(struct work_struct *work)
915 struct cache_set *c = container_of(to_delayed_work(work),
918 spin_lock(&c->journal.lock);
919 if (c->journal.cur->dirty)
920 journal_try_write(c);
922 spin_unlock(&c->journal.lock);
926 * Entry point to the journalling code - bio_insert() and btree_invalidate()
927 * pass bch_journal() a list of keys to be journalled, and then
928 * bch_journal() hands those same keys off to btree_insert_async()
931 atomic_t *bch_journal(struct cache_set *c,
932 struct keylist *keys,
933 struct closure *parent)
935 struct journal_write *w;
938 /* No journaling if CACHE_SET_IO_DISABLE set already */
939 if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags)))
942 if (!CACHE_SYNC(&c->sb))
945 w = journal_wait_for_write(c, bch_keylist_nkeys(keys));
947 memcpy(bset_bkey_last(w->data), keys->keys, bch_keylist_bytes(keys));
948 w->data->keys += bch_keylist_nkeys(keys);
950 ret = &fifo_back(&c->journal.pin);
954 closure_wait(&w->wait, parent);
955 journal_try_write(c);
956 } else if (!w->dirty) {
958 schedule_delayed_work(&c->journal.work,
959 msecs_to_jiffies(c->journal_delay_ms));
960 spin_unlock(&c->journal.lock);
962 spin_unlock(&c->journal.lock);
969 void bch_journal_meta(struct cache_set *c, struct closure *cl)
974 bch_keylist_init(&keys);
976 ref = bch_journal(c, &keys, cl);
981 void bch_journal_free(struct cache_set *c)
983 free_pages((unsigned long) c->journal.w[1].data, JSET_BITS);
984 free_pages((unsigned long) c->journal.w[0].data, JSET_BITS);
985 free_fifo(&c->journal.pin);
988 int bch_journal_alloc(struct cache_set *c)
990 struct journal *j = &c->journal;
992 spin_lock_init(&j->lock);
993 spin_lock_init(&j->flush_write_lock);
994 INIT_DELAYED_WORK(&j->work, journal_write_work);
996 c->journal_delay_ms = 100;
1001 if (!(init_fifo(&j->pin, JOURNAL_PIN, GFP_KERNEL)) ||
1002 !(j->w[0].data = (void *) __get_free_pages(GFP_KERNEL, JSET_BITS)) ||
1003 !(j->w[1].data = (void *) __get_free_pages(GFP_KERNEL, JSET_BITS)))