Merge bitcoin/bitcoin#32530: node: cap -maxmempool and -dbcache values for 32-bit

9f8e7b0 node: cap -dbcache to 1GiB on 32-bit architectures (Antoine Poinsot)
2c43b6a init: cap -maxmempool to 500 MB on 32-bit systems (Antoine Poinsot)

Pull request description:

  32-bit architecture is limited to 4GiB of RAM, so it doesn't make sense to set a too high value. A too high value could cause an OOM unbeknownst to the user a while after startup as mempool / dbcache fills.

ACKs for top commit:
  achow101:
    ACK 9f8e7b0
  instagibbs:
    utACK 9f8e7b0
  dergoegge:
    Code review ACK 9f8e7b0
  glozow:
    utACK 9f8e7b0

Tree-SHA512: cc7541b2c0040fc21a43916caec464dfb443af808f4e85deffa1187448ffff6edb0d69f9ebdb43915d145b8b4694d8465afe548f88da53ccebc9ce4b7c34b735

Author: fanquake

src/node/caches.cpp

@@ -19,6 +19,8 @@
 static constexpr size_t MAX_TX_INDEX_CACHE{1024_MiB};
 //! Max memory allocated to all block filter index caches combined in bytes.
 static constexpr size_t MAX_FILTER_INDEX_CACHE{1024_MiB};
+//! Maximum dbcache size on 32-bit systems.
+static constexpr size_t MAX_32BIT_DBCACHE{1024_MiB};
 
 namespace node {
 CacheSizes CalculateCacheSizes(const ArgsManager& args, size_t n_indexes)
@@ -28,7 +30,8 @@ CacheSizes CalculateCacheSizes(const ArgsManager& args, size_t n_indexes)
     if (std::optional<int64_t> db_cache = args.GetIntArg("-dbcache")) {
         if (*db_cache < 0) db_cache = 0;
         uint64_t db_cache_bytes = SaturatingLeftShift<uint64_t>(*db_cache, 20);
-        total_cache = std::max<size_t>(MIN_DB_CACHE, std::min<uint64_t>(db_cache_bytes, std::numeric_limits<size_t>::max()));
+        constexpr auto max_db_cache{sizeof(void*) == 4 ? MAX_32BIT_DBCACHE : std::numeric_limits<size_t>::max()};
+        total_cache = std::max<size_t>(MIN_DB_CACHE, std::min<uint64_t>(db_cache_bytes, max_db_cache));
     }
 
     IndexCacheSizes index_sizes;

src/node/mempool_args.cpp

@@ -25,6 +25,9 @@ using common::AmountErrMsg;
 using kernel::MemPoolLimits;
 using kernel::MemPoolOptions;
 
+//! Maximum mempool size on 32-bit systems.
+static constexpr int MAX_32BIT_MEMPOOL_MB{500};
+
 namespace {
 void ApplyArgsManOptions(const ArgsManager& argsman, MemPoolLimits& mempool_limits)
 {
@@ -42,7 +45,13 @@ util::Result<void> ApplyArgsManOptions(const ArgsManager& argsman, const CChainP
 {
     mempool_opts.check_ratio = argsman.GetIntArg("-checkmempool", mempool_opts.check_ratio);
 
-    if (auto mb = argsman.GetIntArg("-maxmempool")) mempool_opts.max_size_bytes = *mb * 1'000'000;
+    if (auto mb = argsman.GetIntArg("-maxmempool")) {
+        constexpr bool is_32bit{sizeof(void*) == 4};
+        if (is_32bit && *mb > MAX_32BIT_MEMPOOL_MB) {
+            return util::Error{Untranslated(strprintf("-maxmempool is set to %i but can't be over %i MB on 32-bit systems", *mb, MAX_32BIT_MEMPOOL_MB))};
+        }
+        mempool_opts.max_size_bytes = *mb * 1'000'000;
+    }
 
     if (auto hours = argsman.GetIntArg("-mempoolexpiry")) mempool_opts.expiry = std::chrono::hours{*hours};