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Diffstat (limited to 'drivers/md/bcache/writeback.c')
-rw-r--r--drivers/md/bcache/writeback.c203
1 files changed, 161 insertions, 42 deletions
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 56a3788..51306a1 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -18,17 +18,39 @@
#include <trace/events/bcache.h>
/* Rate limiting */
-
-static void __update_writeback_rate(struct cached_dev *dc)
+static uint64_t __calc_target_rate(struct cached_dev *dc)
{
struct cache_set *c = dc->disk.c;
+
+ /*
+ * This is the size of the cache, minus the amount used for
+ * flash-only devices
+ */
uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size -
bcache_flash_devs_sectors_dirty(c);
+
+ /*
+ * Unfortunately there is no control of global dirty data. If the
+ * user states that they want 10% dirty data in the cache, and has,
+ * e.g., 5 backing volumes of equal size, we try and ensure each
+ * backing volume uses about 2% of the cache for dirty data.
+ */
+ uint32_t bdev_share =
+ div64_u64(bdev_sectors(dc->bdev) << WRITEBACK_SHARE_SHIFT,
+ c->cached_dev_sectors);
+
uint64_t cache_dirty_target =
div_u64(cache_sectors * dc->writeback_percent, 100);
- int64_t target = div64_u64(cache_dirty_target * bdev_sectors(dc->bdev),
- c->cached_dev_sectors);
+ /* Ensure each backing dev gets at least one dirty share */
+ if (bdev_share < 1)
+ bdev_share = 1;
+
+ return (cache_dirty_target * bdev_share) >> WRITEBACK_SHARE_SHIFT;
+}
+
+static void __update_writeback_rate(struct cached_dev *dc)
+{
/*
* PI controller:
* Figures out the amount that should be written per second.
@@ -49,6 +71,7 @@ static void __update_writeback_rate(struct cached_dev *dc)
* This acts as a slow, long-term average that is not subject to
* variations in usage like the p term.
*/
+ int64_t target = __calc_target_rate(dc);
int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
int64_t error = dirty - target;
int64_t proportional_scaled =
@@ -116,6 +139,7 @@ static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
struct dirty_io {
struct closure cl;
struct cached_dev *dc;
+ uint16_t sequence;
struct bio bio;
};
@@ -194,6 +218,27 @@ static void write_dirty(struct closure *cl)
{
struct dirty_io *io = container_of(cl, struct dirty_io, cl);
struct keybuf_key *w = io->bio.bi_private;
+ struct cached_dev *dc = io->dc;
+
+ uint16_t next_sequence;
+
+ if (atomic_read(&dc->writeback_sequence_next) != io->sequence) {
+ /* Not our turn to write; wait for a write to complete */
+ closure_wait(&dc->writeback_ordering_wait, cl);
+
+ if (atomic_read(&dc->writeback_sequence_next) == io->sequence) {
+ /*
+ * Edge case-- it happened in indeterminate order
+ * relative to when we were added to wait list..
+ */
+ closure_wake_up(&dc->writeback_ordering_wait);
+ }
+
+ continue_at(cl, write_dirty, io->dc->writeback_write_wq);
+ return;
+ }
+
+ next_sequence = io->sequence + 1;
/*
* IO errors are signalled using the dirty bit on the key.
@@ -211,6 +256,9 @@ static void write_dirty(struct closure *cl)
closure_bio_submit(&io->bio, cl);
}
+ atomic_set(&dc->writeback_sequence_next, next_sequence);
+ closure_wake_up(&dc->writeback_ordering_wait);
+
continue_at(cl, write_dirty_finish, io->dc->writeback_write_wq);
}
@@ -219,8 +267,10 @@ static void read_dirty_endio(struct bio *bio)
struct keybuf_key *w = bio->bi_private;
struct dirty_io *io = w->private;
+ /* is_read = 1 */
bch_count_io_errors(PTR_CACHE(io->dc->disk.c, &w->key, 0),
- bio->bi_status, "reading dirty data from cache");
+ bio->bi_status, 1,
+ "reading dirty data from cache");
dirty_endio(bio);
}
@@ -237,10 +287,15 @@ static void read_dirty_submit(struct closure *cl)
static void read_dirty(struct cached_dev *dc)
{
unsigned delay = 0;
- struct keybuf_key *w;
+ struct keybuf_key *next, *keys[MAX_WRITEBACKS_IN_PASS], *w;
+ size_t size;
+ int nk, i;
struct dirty_io *io;
struct closure cl;
+ uint16_t sequence = 0;
+ BUG_ON(!llist_empty(&dc->writeback_ordering_wait.list));
+ atomic_set(&dc->writeback_sequence_next, sequence);
closure_init_stack(&cl);
/*
@@ -248,45 +303,109 @@ static void read_dirty(struct cached_dev *dc)
* mempools.
*/
- while (!kthread_should_stop()) {
-
- w = bch_keybuf_next(&dc->writeback_keys);
- if (!w)
- break;
-
- BUG_ON(ptr_stale(dc->disk.c, &w->key, 0));
-
- if (KEY_START(&w->key) != dc->last_read ||
- jiffies_to_msecs(delay) > 50)
- while (!kthread_should_stop() && delay)
- delay = schedule_timeout_interruptible(delay);
-
- dc->last_read = KEY_OFFSET(&w->key);
-
- io = kzalloc(sizeof(struct dirty_io) + sizeof(struct bio_vec)
- * DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
- GFP_KERNEL);
- if (!io)
- goto err;
-
- w->private = io;
- io->dc = dc;
-
- dirty_init(w);
- bio_set_op_attrs(&io->bio, REQ_OP_READ, 0);
- io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0);
- bio_set_dev(&io->bio, PTR_CACHE(dc->disk.c, &w->key, 0)->bdev);
- io->bio.bi_end_io = read_dirty_endio;
-
- if (bio_alloc_pages(&io->bio, GFP_KERNEL))
- goto err_free;
+ next = bch_keybuf_next(&dc->writeback_keys);
+
+ while (!kthread_should_stop() && next) {
+ size = 0;
+ nk = 0;
+
+ do {
+ BUG_ON(ptr_stale(dc->disk.c, &next->key, 0));
+
+ /*
+ * Don't combine too many operations, even if they
+ * are all small.
+ */
+ if (nk >= MAX_WRITEBACKS_IN_PASS)
+ break;
+
+ /*
+ * If the current operation is very large, don't
+ * further combine operations.
+ */
+ if (size >= MAX_WRITESIZE_IN_PASS)
+ break;
+
+ /*
+ * Operations are only eligible to be combined
+ * if they are contiguous.
+ *
+ * TODO: add a heuristic willing to fire a
+ * certain amount of non-contiguous IO per pass,
+ * so that we can benefit from backing device
+ * command queueing.
+ */
+ if ((nk != 0) && bkey_cmp(&keys[nk-1]->key,
+ &START_KEY(&next->key)))
+ break;
+
+ size += KEY_SIZE(&next->key);
+ keys[nk++] = next;
+ } while ((next = bch_keybuf_next(&dc->writeback_keys)));
+
+ /* Now we have gathered a set of 1..5 keys to write back. */
+ for (i = 0; i < nk; i++) {
+ w = keys[i];
+
+ io = kzalloc(sizeof(struct dirty_io) +
+ sizeof(struct bio_vec) *
+ DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
+ GFP_KERNEL);
+ if (!io)
+ goto err;
+
+ w->private = io;
+ io->dc = dc;
+ io->sequence = sequence++;
+
+ dirty_init(w);
+ bio_set_op_attrs(&io->bio, REQ_OP_READ, 0);
+ io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0);
+ bio_set_dev(&io->bio,
+ PTR_CACHE(dc->disk.c, &w->key, 0)->bdev);
+ io->bio.bi_end_io = read_dirty_endio;
+
+ if (bch_bio_alloc_pages(&io->bio, GFP_KERNEL))
+ goto err_free;
+
+ trace_bcache_writeback(&w->key);
+
+ down(&dc->in_flight);
+
+ /* We've acquired a semaphore for the maximum
+ * simultaneous number of writebacks; from here
+ * everything happens asynchronously.
+ */
+ closure_call(&io->cl, read_dirty_submit, NULL, &cl);
+ }
- trace_bcache_writeback(&w->key);
+ delay = writeback_delay(dc, size);
- down(&dc->in_flight);
- closure_call(&io->cl, read_dirty_submit, NULL, &cl);
+ /* If the control system would wait for at least half a
+ * second, and there's been no reqs hitting the backing disk
+ * for awhile: use an alternate mode where we have at most
+ * one contiguous set of writebacks in flight at a time. If
+ * someone wants to do IO it will be quick, as it will only
+ * have to contend with one operation in flight, and we'll
+ * be round-tripping data to the backing disk as quickly as
+ * it can accept it.
+ */
+ if (delay >= HZ / 2) {
+ /* 3 means at least 1.5 seconds, up to 7.5 if we
+ * have slowed way down.
+ */
+ if (atomic_inc_return(&dc->backing_idle) >= 3) {
+ /* Wait for current I/Os to finish */
+ closure_sync(&cl);
+ /* And immediately launch a new set. */
+ delay = 0;
+ }
+ }
- delay = writeback_delay(dc, KEY_SIZE(&w->key));
+ while (!kthread_should_stop() && delay) {
+ schedule_timeout_interruptible(delay);
+ delay = writeback_delay(dc, 0);
+ }
}
if (0) {
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