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

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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.
This commit is contained in:
Ondřej Surý 2026-02-19 10:24:13 +01:00
parent 6fa415f71f
commit dc9564f14d
4 changed files with 11 additions and 14 deletions
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12
bin/named/server.c
View file

@ -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

9
doc/arm/reference.rst
View file

@ -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::

2
lib/dns/include/dns/adb.h
View file

@ -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

2
lib/dns/include/dns/cache.h
View file

@ -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