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

9f8e7b0b3b787b873045a4a8194e77d0b0a2b3b6 node: cap -dbcache to 1GiB on 32-bit architectures (Antoine Poinsot)
2c43b6adebbfabb3c8dd82fe821ce0a5d6173b3b 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:
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  instagibbs:
    utACK 9f8e7b0b3b787b873045a4a8194e77d0b0a2b3b6
  dergoegge:
    Code review ACK 9f8e7b0b3b787b873045a4a8194e77d0b0a2b3b6
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Tree-SHA512: cc7541b2c0040fc21a43916caec464dfb443af808f4e85deffa1187448ffff6edb0d69f9ebdb43915d145b8b4694d8465afe548f88da53ccebc9ce4b7c34b735

Author: fanquake

src/init.cpp

@@ -131,6 +131,7 @@ static const bool DEFAULT_REST_ENABLE = false;
 #endif
 
 static const char* DEFAULT_ASMAP_FILENAME="ip_asn.map";
+static constexpr int MAX_32BIT_MEMPOOL_MB{500};
 
 /**
  * The PID file facilities.
@@ -976,6 +977,10 @@ bool AppInitParameterInteraction(const ArgsManager& args)
     int64_t nMempoolSizeMin = args.GetIntArg("-limitdescendantsize", DEFAULT_DESCENDANT_SIZE_LIMIT) * 1000 * 40;
     if (nMempoolSizeMax < 0 || nMempoolSizeMax < nMempoolSizeMin)
         return InitError(strprintf(_("-maxmempool must be at least %d MB"), std::ceil(nMempoolSizeMin / 1000000.0)));
+    constexpr bool is_32bit{sizeof(void*) == 4};
+    if (is_32bit && nMempoolSizeMax > MAX_32BIT_MEMPOOL_MB) {
+        return InitError(strprintf(_("-maxmempool is set to %i but can't be over %i MB on 32-bit systems"), nMempoolSizeMax, MAX_32BIT_MEMPOOL_MB));
+    }
     // incremental relay fee sets the minimum feerate increase necessary for BIP 125 replacement in the mempool
     // and the amount the mempool min fee increases above the feerate of txs evicted due to mempool limiting.
     if (args.IsArgSet("-incrementalrelayfee")) {

src/node/caches.cpp

@@ -8,12 +8,16 @@
 #include <util/system.h>
 #include <validation.h>
 
+//! Maximum dbcache size on 32-bit systems.
+static constexpr int64_t MAX_32BIT_DBCACHE = 1ULL << 30;  // 1 GiB
+
 namespace node {
 CacheSizes CalculateCacheSizes(const ArgsManager& args, size_t n_indexes)
 {
     int64_t nTotalCache = (args.GetIntArg("-dbcache", nDefaultDbCache) << 20);
     nTotalCache = std::max(nTotalCache, nMinDbCache << 20); // total cache cannot be less than nMinDbCache
     nTotalCache = std::min(nTotalCache, nMaxDbCache << 20); // total cache cannot be greater than nMaxDbcache
+    if (sizeof(void*) == 4) nTotalCache = std::min(nTotalCache, MAX_32BIT_DBCACHE);
     CacheSizes sizes;
     sizes.block_tree_db = std::min(nTotalCache / 8, nMaxBlockDBCache << 20);
     nTotalCache -= sizes.block_tree_db;