Raise the minimum cache size to 8 MB, warn below 256 MB

Lower the hard floor for max-cache-size from 2 MB to 8 MB to support
resource-constrained environments (e.g. CPE devices) while remaining
safe for LRU-only eviction.

diff --git a/bin/named/server.c b/bin/named/server.c
index 5d82a7ac349025d70e3f409858591f33a4e36afb..71a9bc2f21d9a9e616ea38bfdacaeb3b52c6aea0 100644 (file)
--- a/bin/named/server.c
+++ b/bin/named/server.c
@@ -3610,10 +3610,6 @@ default_max_cache_size(const dns_view_t *view, const cfg_obj_t *obj) {
 
 static size_t
 sanitized_max_cache_size(const cfg_obj_t *obj, uint64_t value) {
-       if (value >= DNS_CACHE_MINSIZE && value <= SIZE_MAX) {
-               return value;
-       }
-
        if (value > SIZE_MAX) {
                cfg_obj_log(obj, ISC_LOG_WARNING,
                            "'max-cache-size %" PRIu64 "' "
@@ -3624,13 +3620,13 @@ sanitized_max_cache_size(const cfg_obj_t *obj, uint64_t value) {
 
        if (value < DNS_CACHE_MINSIZE) {
                cfg_obj_log(obj, ISC_LOG_WARNING,
-                           "'max-cache-size' can't be less than %" PRIu64 "; "
-                           "setting 'max-cache-size' to the minimum value",
-                           DNS_CACHE_MINSIZE);
+                           "'max-cache-size %" PRIu64 "' "
+                           "is too small; setting to %" PRIu64,
+                           value, DNS_CACHE_MINSIZE);
                return DNS_CACHE_MINSIZE;
        }
 
-       UNREACHABLE();
+       return value;
 }
 
 static size_t

diff --git a/doc/arm/reference.rst b/doc/arm/reference.rst
index 9964718dd65fe9753819e00829419074416df107..ee4533146747dede2e24828c9a8a3468b571537a 100644 (file)
--- a/doc/arm/reference.rst
+++ b/doc/arm/reference.rst
@@ -3847,10 +3847,11 @@ system.
        default value of that option (90% of physical memory for each
        individual cache) may lead to memory exhaustion over time.
 
-   .. note::
+   .. warning::
 
-       :any:`max-cache-size` does not work reliably for a maximum
-       amount of memory of 256 MB or lower.
+       Setting :any:`max-cache-size` to a value lower than 256 MB is
+       permitted but not recommended; LRU-only cache eviction may cause
+       excessive churn under load.
 
    Upon startup and reconfiguration, caches with a limited size
    preallocate a small amount of memory (less than 1% of
@@ -3859,7 +3860,7 @@ system.
    internal cache structures.
 
    On systems where detection of the amount of physical memory is not
-   supported, the :iscman:`named` will fail to start.
+   supported, :iscman:`named` will fall back to the minimum value (2 MB).
 
    .. note::
 

diff --git a/lib/dns/include/dns/adb.h b/lib/dns/include/dns/adb.h
index 2f88c9beca4873e044c6d02cb53167db7eccf498..7c1aef4cc5d831a32ef8856c63cb58c9ac8c402d 100644 (file)
--- a/lib/dns/include/dns/adb.h
+++ b/lib/dns/include/dns/adb.h
@@ -83,7 +83,7 @@
 #define DNS_ADBADDRINFO_MAGIC   ISC_MAGIC('a', 'd', 'A', 'I')
 #define DNS_ADBADDRINFO_VALID(x) ISC_MAGIC_VALID(x, DNS_ADBADDRINFO_MAGIC)
 
-#define DNS_ADB_MINADBSIZE (1024U * 1024U) /*%< 1 Megabyte */
+#define DNS_ADB_MINADBSIZE UINT64_C(1024 * 1024) /*%< 1 MB */
 
 /***
  *** TYPES

diff --git a/lib/dns/include/dns/cache.h b/lib/dns/include/dns/cache.h
index 8949fce462e147d808e52784bc545dce44d21656..1ac822ad717f42beafbd82c37d09f4790732481f 100644 (file)
--- a/lib/dns/include/dns/cache.h
+++ b/lib/dns/include/dns/cache.h
@@ -56,7 +56,7 @@
  * DNS_CACHE_MINSIZE is how many bytes is the floor for
  * dns_cache_setcachesize().
  */
-#define DNS_CACHE_MINSIZE UINT64_C(2097152) /*%< Bytes.  2097152 = 2 MB */
+#define DNS_CACHE_MINSIZE UINT64_C(2 * 1024 * 1024) /*%< Bytes. 2 MB */
 
 /***
  ***   Functions