mempool: Introduce (still-unused) MemPoolLimits

They live as a CTxMemPool member.

[META] These limits will be used in subsequent commits to replace calls
       to gArgs.

src/Makefile.am

@@ -173,6 +173,7 @@ BITCOIN_CORE_H = \
   kernel/checks.h \
   kernel/coinstats.h \
   kernel/context.h \
+  kernel/mempool_limits.h \
   kernel/mempool_options.h \
   key.h \
   key_io.h \

src/kernel/mempool_limits.h

@@ -0,0 +1,26 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#ifndef BITCOIN_KERNEL_MEMPOOL_LIMITS_H
+#define BITCOIN_KERNEL_MEMPOOL_LIMITS_H
+
+#include <policy/policy.h>
+
+#include <cstdint>
+
+namespace kernel {
+/**
+ * Options struct containing limit options for a CTxMemPool. Default constructor
+ * populates the struct with sane default values which can be modified.
+ *
+ * Most of the time, this struct should be referenced as CTxMemPool::Limits.
+ */
+struct MemPoolLimits {
+    int64_t ancestor_count{DEFAULT_ANCESTOR_LIMIT};
+    int64_t ancestor_size_vbytes{DEFAULT_ANCESTOR_SIZE_LIMIT_KVB * 1'000};
+    int64_t descendant_count{DEFAULT_DESCENDANT_LIMIT};
+    int64_t descendant_size_vbytes{DEFAULT_DESCENDANT_SIZE_LIMIT_KVB * 1'000};
+};
+} // namespace kernel
+
+#endif // BITCOIN_KERNEL_MEMPOOL_LIMITS_H

src/kernel/mempool_options.h

@@ -4,6 +4,8 @@
 #ifndef BITCOIN_KERNEL_MEMPOOL_OPTIONS_H
 #define BITCOIN_KERNEL_MEMPOOL_OPTIONS_H
 
+#include <kernel/mempool_limits.h>
+
 #include <chrono>
 #include <cstdint>
 
@@ -29,6 +31,7 @@ struct MemPoolOptions {
     int check_ratio{0};
     int64_t max_size_bytes{DEFAULT_MAX_MEMPOOL_SIZE_MB * 1'000'000};
     std::chrono::seconds expiry{std::chrono::hours{DEFAULT_MEMPOOL_EXPIRY_HOURS}};
+    MemPoolLimits limits{};
 };
 } // namespace kernel
 

src/mempool_args.cpp

@@ -4,12 +4,27 @@
 
 #include <mempool_args.h>
 
+#include <kernel/mempool_limits.h>
 #include <kernel/mempool_options.h>
 
 #include <util/system.h>
 
+using kernel::MemPoolLimits;
 using kernel::MemPoolOptions;
 
+namespace {
+void ApplyArgsManOptions(const ArgsManager& argsman, MemPoolLimits& mempool_limits)
+{
+    mempool_limits.ancestor_count = argsman.GetIntArg("-limitancestorcount", mempool_limits.ancestor_count);
+
+    if (auto vkb = argsman.GetIntArg("-limitancestorsize")) mempool_limits.ancestor_size_vbytes = *vkb * 1'000;
+
+    mempool_limits.descendant_count = argsman.GetIntArg("-limitdescendantcount", mempool_limits.descendant_count);
+
+    if (auto vkb = argsman.GetIntArg("-limitdescendantsize")) mempool_limits.descendant_size_vbytes = *vkb * 1'000;
+}
+}
+
 void ApplyArgsManOptions(const ArgsManager& argsman, MemPoolOptions& mempool_opts)
 {
     mempool_opts.check_ratio = argsman.GetIntArg("-checkmempool", mempool_opts.check_ratio);
@@ -17,4 +32,6 @@ void ApplyArgsManOptions(const ArgsManager& argsman, MemPoolOptions& mempool_opt
     if (auto mb = argsman.GetIntArg("-maxmempool")) mempool_opts.max_size_bytes = *mb * 1'000'000;
 
     if (auto hours = argsman.GetIntArg("-mempoolexpiry")) mempool_opts.expiry = std::chrono::hours{*hours};
+
+    ApplyArgsManOptions(argsman, mempool_opts.limits);
 }

src/mempool_args.h

@@ -10,6 +10,13 @@ namespace kernel {
 struct MemPoolOptions;
 };
 
+/**
+ * Overlay the options set in \p argsman on top of corresponding members in \p mempool_opts.
+ *
+ * @param[in]  argsman The ArgsManager in which to check set options.
+ * @param[in,out] mempool_opts The MemPoolOptions to modify according to \p argsman.
+ */
 void ApplyArgsManOptions(const ArgsManager& argsman, kernel::MemPoolOptions& mempool_opts);
 
+
 #endif // BITCOIN_MEMPOOL_ARGS_H

src/txmempool.cpp

@@ -455,7 +455,8 @@ CTxMemPool::CTxMemPool(const Options& opts)
     : m_check_ratio{opts.check_ratio},
       minerPolicyEstimator{opts.estimator},
       m_max_size_bytes{opts.max_size_bytes},
-      m_expiry{opts.expiry}
+      m_expiry{opts.expiry},
+      m_limits{opts.limits}
 {
     _clear(); //lock free clear
 }

src/txmempool.h

@@ -14,6 +14,7 @@
 #include <utility>
 #include <vector>
 
+#include <kernel/mempool_limits.h>
 #include <kernel/mempool_options.h>
 
 #include <coins.h>
@@ -569,6 +570,10 @@ public:
     const int64_t m_max_size_bytes;
     const std::chrono::seconds m_expiry;
 
+    using Limits = kernel::MemPoolLimits;
+
+    const Limits m_limits;
+
     /** Create a new CTxMemPool.
      * Sanity checks will be off by default for performance, because otherwise
      * accepting transactions becomes O(N^2) where N is the number of transactions