Enable client eviction by default, set maxmemory-clients too 100% by default

src/config.c

@@ -3344,7 +3344,7 @@ standardConfig static_configs[] = {
     createSizeTConfig("hll-sparse-max-bytes", NULL, MODIFIABLE_CONFIG, 0, LONG_MAX, server.hll_sparse_max_bytes, 3000, MEMORY_CONFIG, NULL, NULL),
     createSizeTConfig("tracking-table-max-keys", NULL, MODIFIABLE_CONFIG, 0, LONG_MAX, server.tracking_table_max_keys, 1000000, INTEGER_CONFIG, NULL, NULL),                                      /* Default: 1 million keys max. */
     createSizeTConfig("client-query-buffer-limit", NULL, DEBUG_CONFIG | MODIFIABLE_CONFIG, 1024 * 1024, LONG_MAX, server.client_max_querybuf_len, 1024 * 1024 * 1024, MEMORY_CONFIG, NULL, NULL), /* Default: 1GB max query buffer. */
-    createSSizeTConfig("maxmemory-clients", NULL, MODIFIABLE_CONFIG, -100, SSIZE_MAX, server.maxmemory_clients, 0, MEMORY_CONFIG | PERCENT_CONFIG, NULL, applyClientMaxMemoryUsage),
+    createSSizeTConfig("maxmemory-clients", NULL, MODIFIABLE_CONFIG, -100, SSIZE_MAX, server.maxmemory_clients, -100, MEMORY_CONFIG | PERCENT_CONFIG, NULL, applyClientMaxMemoryUsage),
 
     /* Other configs */
     createTimeTConfig("repl-backlog-ttl", NULL, MODIFIABLE_CONFIG, 0, LONG_MAX, server.repl_backlog_time_limit, 60 * 60, INTEGER_CONFIG, NULL, NULL), /* Default: 1 hour */

tests/integration/replication-buffer.tcl

@@ -301,6 +301,7 @@ test "Replica client-output-buffer size is limited to backlog_limit/16 when no r
             set master [srv 0 client]
             set master_host [srv 0 host]
             set master_port [srv 0 port]
+            $master config set maxmemory-clients 0
             $master config set maxmemory-policy allkeys-lru
 
             $master config set repl-backlog-size 16384

valkey.conf

@@ -2303,14 +2303,16 @@ client-output-buffer-limit pubsub 32mb 8mb 60
 # client-query-buffer-limit 1gb
 
 # In some scenarios client connections can hog up memory leading to OOM
-# errors or data eviction. To avoid this we can cap the accumulated memory
+# errors or key eviction from the server perspective. And it may also violate
+# maxmemory and causing the machine to OOM from the process perspective.
+#
+# To avoid or alleviate these problems we can cap the accumulated memory
 # used by all client connections (all pubsub and normal clients). Once we
 # reach that limit connections will be dropped by the server freeing up
 # memory. The server will attempt to drop the connections using the most 
 # memory first. We call this mechanism "client eviction".
 #
 # Client eviction is configured using the maxmemory-clients setting as follows:
-# 0 - client eviction is disabled (default)
 #
 # A memory value can be used for the client eviction threshold,
 # for example:
@@ -2320,6 +2322,9 @@ client-output-buffer-limit pubsub 32mb 8mb 60
 # is based on a percentage of the maxmemory setting. For example to set client
 # eviction at 5% of maxmemory:
 # maxmemory-clients 5%
+#
+# Client eviction is enabled by default and the value is 100% of maxmemory.
+maxmemory-clients 100%
 
 # In the server protocol, bulk requests, that are, elements representing single
 # strings, are normally limited to 512 mb. However you can change this limit