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, 43 insertions, 0 deletions

diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index 5ce9771df047..c91f61bb95b6 100644
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -1,6 +1,9 @@
 #ifndef _BCACHE_WRITEBACK_H
 #define _BCACHE_WRITEBACK_H
 
+#define CUTOFF_WRITEBACK        40
+#define CUTOFF_WRITEBACK_SYNC   70
+
 static inline uint64_t bcache_dev_sectors_dirty(struct bcache_device *d)
 {
         uint64_t i, ret = 0;
@@ -11,6 +14,46 @@ static inline uint64_t bcache_dev_sectors_dirty(struct bcache_device *d)
         return ret;
 }
 
+static inline bool bcache_dev_stripe_dirty(struct bcache_device *d,
+                                           uint64_t offset,
+                                           unsigned nr_sectors)
+{
+        uint64_t stripe = offset >> d->stripe_size_bits;
+
+        while (1) {
+                if (atomic_read(d->stripe_sectors_dirty + stripe))
+                        return true;
+
+                if (nr_sectors <= 1 << d->stripe_size_bits)
+                        return false;
+
+                nr_sectors -= 1 << d->stripe_size_bits;
+                stripe++;
+        }
+}
+
+static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,
+                                    unsigned cache_mode, bool would_skip)
+{
+        unsigned in_use = dc->disk.c->gc_stats.in_use;
+
+        if (cache_mode != CACHE_MODE_WRITEBACK ||
+            atomic_read(&dc->disk.detaching) ||
+            in_use > CUTOFF_WRITEBACK_SYNC)
+                return false;
+
+        if (dc->partial_stripes_expensive &&
+            bcache_dev_stripe_dirty(&dc->disk, bio->bi_sector,
+                                    bio_sectors(bio)))
+                return true;
+
+        if (would_skip)
+                return false;
+
+        return bio->bi_rw & REQ_SYNC ||
+                in_use <= CUTOFF_WRITEBACK;
+}
+
 void bcache_dev_sectors_dirty_add(struct cache_set *, unsigned, uint64_t, int);
 void bch_writeback_queue(struct cached_dev *);
 void bch_writeback_add(struct cached_dev *);