bcache: Write out full stripes

Now that we're tracking dirty data per stripe, we can add two
optimizations for raid5/6:

 * If a stripe is already dirty, force writes to that stripe to
   writeback mode - to help build up full stripes of dirty data

 * When flushing dirty data, preferentially write out full stripes first
   if there are any.

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

1 files changed, 42 insertions, 2 deletions

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index dd815475c524..d81ee5ccc726 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -108,6 +108,31 @@ static bool dirty_pred(struct keybuf *buf, struct bkey *k)
         return KEY_DIRTY(k);
 }
 
+static bool dirty_full_stripe_pred(struct keybuf *buf, struct bkey *k)
+{
+        uint64_t stripe;
+        unsigned nr_sectors = KEY_SIZE(k);
+        struct cached_dev *dc = container_of(buf, struct cached_dev,
+                                             writeback_keys);
+        unsigned stripe_size = 1 << dc->disk.stripe_size_bits;
+
+        if (!KEY_DIRTY(k))
+                return false;
+
+        stripe = KEY_START(k) >> dc->disk.stripe_size_bits;
+        while (1) {
+                if (atomic_read(dc->disk.stripe_sectors_dirty + stripe) !=
+                    stripe_size)
+                        return false;
+
+                if (nr_sectors <= stripe_size)
+                        return true;
+
+                nr_sectors -= stripe_size;
+                stripe++;
+        }
+}
+
 static void dirty_init(struct keybuf_key *w)
 {
         struct dirty_io *io = w->private;
@@ -152,7 +177,22 @@ static void refill_dirty(struct closure *cl)
                 searched_from_start = true;
         }
 
-        bch_refill_keybuf(dc->disk.c, buf, &end);
+        if (dc->partial_stripes_expensive) {
+                uint64_t i;
+
+                for (i = 0; i < dc->disk.nr_stripes; i++)
+                        if (atomic_read(dc->disk.stripe_sectors_dirty + i) ==
+                            1 << dc->disk.stripe_size_bits)
+                                goto full_stripes;
+
+                goto normal_refill;
+full_stripes:
+                bch_refill_keybuf(dc->disk.c, buf, &end,
+                                  dirty_full_stripe_pred);
+        } else {
+normal_refill:
+                bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
+        }
 
         if (bkey_cmp(&buf->last_scanned, &end) >= 0 && searched_from_start) {
                 /* Searched the entire btree  - delay awhile */
@@ -446,7 +486,7 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc)
         closure_init_unlocked(&dc->writeback);
         init_rwsem(&dc->writeback_lock);
 
-        bch_keybuf_init(&dc->writeback_keys, dirty_pred);
+        bch_keybuf_init(&dc->writeback_keys);
 
         dc->writeback_metadata          = true;
         dc->writeback_running           = true;