[ltt-dev] [PATCH 4/6] rculfhash: Change lazy shrink strategy

[Lai Jiangshan]

We can aggressively grow a ht,
but we should conservatively shrink a ht.

When we try to shrink the ht after a deletion,
but if a growing is required after it, we should
stop this shrink.

But it is more complicated to implement it, so we use more
conservative strategy to shrink a ht to gain simple code:

We stop to (lazy) shrink when we found growing is
in progress.

Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
---
 rculfhash.c |   29 ++++++++++++++++++++++++++++-
 1 files changed, 28 insertions(+), 1 deletions(-)

diff --git a/rculfhash.c b/rculfhash.c
index c12ee10..5ff832d 100644
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -1797,6 +1797,33 @@ void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size,
 	if (!(ht->flags & CDS_LFHT_AUTO_RESIZE))
 		return;
 
-	resize_target_update_count(ht, count);
+	count = max(count, ht->min_alloc_size);
+	if (count == size)
+		return;
+
+	if (count > size) { /* lazy grow */
+		if (resize_target_grow(ht, count) >= count)
+			return;
+	} else { /* lazy shrink */
+		for (;;) {
+			unsigned long s;
+
+			s = uatomic_cmpxchg(&ht->t.resize_target, size, count);
+
+			if (s == size)
+				break;
+
+			/* growing is/(was just) in progress */
+			if (s > size)
+				return;
+
+			/* some other thread do shrink for me*/
+			if (s <= count)
+				return;
+
+			size = s;
+		}
+	}
+
 	__cds_lfht_resize_lazy_launch(ht);
 }
-- 
1.7.4.4