bcache: Improve lazy sorting

The old lazy sorting code was kind of hacky - rewrite in a way that
mathematically makes more sense; the idea is that the size of the sets
of keys in a btree node should increase by a more or less fixed ratio
from smallest to biggest.

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

3 files changed, 26 insertions, 17 deletions

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 59c15e09e4dd..6fa5a1e33c49 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -828,6 +828,7 @@ struct cache_set {
          */
         struct mutex            sort_lock;
         struct bset             *sort;
+        unsigned                sort_crit_factor;
 
         /* List of buckets we're currently writing data to */
         struct list_head        data_buckets;
diff --git a/drivers/md/bcache/bset.c b/drivers/md/bcache/bset.c
index e9399ed7f688..a0f190ac17a4 100644
--- a/drivers/md/bcache/bset.c
+++ b/drivers/md/bcache/bset.c
@@ -1092,33 +1092,39 @@ void bch_btree_sort_into(struct btree *b, struct btree *new)
         new->sets->size = 0;
 }
 
+#define SORT_CRIT       (4096 / sizeof(uint64_t))
+
 void bch_btree_sort_lazy(struct btree *b)
 {
-        if (b->nsets) {
-                unsigned i, j, keys = 0, total;
-
-                for (i = 0; i <= b->nsets; i++)
-                        keys += b->sets[i].data->keys;
+        unsigned crit = SORT_CRIT;
+        int i;
 
-                total = keys;
+        /* Don't sort if nothing to do */
+        if (!b->nsets)
+                goto out;
 
-                for (j = 0; j < b->nsets; j++) {
-                        if (keys * 2 < total ||
-                            keys < 1000) {
-                                bch_btree_sort_partial(b, j);
-                                return;
-                        }
+        /* If not a leaf node, always sort */
+        if (b->level) {
+                bch_btree_sort(b);
+                return;
+        }
 
-                        keys -= b->sets[j].data->keys;
-                }
+        for (i = b->nsets - 1; i >= 0; --i) {
+                crit *= b->c->sort_crit_factor;
 
-                /* Must sort if b->nsets == 3 or we'll overflow */
-                if (b->nsets >= (MAX_BSETS - 1) - b->level) {
-                        bch_btree_sort(b);
+                if (b->sets[i].data->keys < crit) {
+                        bch_btree_sort_partial(b, i);
                         return;
                 }
         }
 
+        /* Sort if we'd overflow */
+        if (b->nsets + 1 == MAX_BSETS) {
+                bch_btree_sort(b);
+                return;
+        }
+
+out:
         bset_build_written_tree(b);
 }
 
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index f24c2e0cbb1c..3c8474161e8e 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1375,6 +1375,8 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
                 c->btree_pages = max_t(int, c->btree_pages / 4,
                                        BTREE_MAX_PAGES);
 
+        c->sort_crit_factor = int_sqrt(c->btree_pages);
+
         mutex_init(&c->bucket_lock);
         mutex_init(&c->sort_lock);
         spin_lock_init(&c->sort_time_lock);