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diff --git a/src/mongo/db/query/util/memory_util.cpp b/src/mongo/db/query/util/memory_util.cpp
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+++ b/src/mongo/db/query/util/memory_util.cpp
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+/**
+ *    Copyright (C) 2021-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kQuery
+
+#include "mongo/db/query/util/memory_util.h"
+
+#include <cstddef>
+#include <pcrecpp.h>
+
+#include "mongo/logv2/log.h"
+#include "mongo/util/processinfo.h"
+
+
+namespace mongo::memory_util {
+
+StatusWith<MemoryUnits> parseUnitString(const std::string& strUnit) {
+    if (strUnit.empty()) {
+        return Status(ErrorCodes::Error{6007010}, "Unit value cannot be empty");
+    }
+
+    if (strUnit[0] == '%') {
+        return MemoryUnits::kPercent;
+    } else if (strUnit[0] == 'M' || strUnit[0] == 'm') {
+        return MemoryUnits::kMB;
+    } else if (strUnit[0] == 'G' || strUnit[0] == 'g') {
+        return MemoryUnits::kGB;
+    }
+
+    return Status(ErrorCodes::Error{6007011}, "Incorrect unit value");
+}
+
+StatusWith<MemorySize> MemorySize::parse(const std::string& str) {
+    pcrecpp::RE_Options opt;
+    opt.set_caseless(true);
+    // Looks for a floating point number with followed by a unit suffix (MB, GB, %).
+    pcrecpp::RE re("\\s*(\\d+\\.?\\d*)\\s*(MB|GB|%)\\s*", opt);
+
+    double size{};
+    std::string strUnit{};
+    if (!re.FullMatch(str, &size, &strUnit)) {
+        return {ErrorCodes::Error{6007012}, "Unable to parse memory size string"};
+    }
+
+    auto statusWithUnit = parseUnitString(strUnit);
+    if (!statusWithUnit.isOK()) {
+        return statusWithUnit.getStatus();
+    }
+    return MemorySize{size, statusWithUnit.getValue()};
+}
+
+size_t convertToSizeInBytes(const MemorySize& memSize) {
+    constexpr size_t kBytesInMB = 1024 * 1024;
+    constexpr size_t kMBytesInGB = 1024;
+
+    double sizeInMB = memSize.size;
+
+    switch (memSize.units) {
+        case MemoryUnits::kPercent:
+            sizeInMB *= ProcessInfo::getMemSizeMB() / 100.0;
+            break;
+        case MemoryUnits::kMB:
+            break;
+        case MemoryUnits::kGB:
+            sizeInMB *= kMBytesInGB;
+            break;
+    }
+
+    return static_cast<size_t>(sizeInMB * kBytesInMB);
+}
+
+size_t getRequestedMemSizeInBytes(const MemorySize& memSize) {
+    size_t planCacheSize = convertToSizeInBytes(memSize);
+    uassert(5968001,
+            "Cache size must be at least 1KB * number of cores",
+            planCacheSize >= 1024 * ProcessInfo::getNumCores());
+    return planCacheSize;
+}
+
+/**
+ * Sets upper limit on a storage structure's size. Either that structure's maximumSize or to
+ * percentage of the total system's memory (both known at call site), whichever is smaller.
+ */
+size_t capMemorySize(size_t requestedSizeBytes,
+                     size_t maximumSizeGB,
+                     double percentTotalSystemMemory) {
+    constexpr size_t kBytesInGB = 1024 * 1024 * 1024;
+    // Express maximum size in bytes.
+    const size_t maximumSizeBytes = maximumSizeGB * kBytesInGB;
+    const memory_util::MemorySize limitToProcessSize{percentTotalSystemMemory,
+                                                     memory_util::MemoryUnits::kPercent};
+    const size_t limitToProcessSizeInBytes = convertToSizeInBytes(limitToProcessSize);
+
+    // The size will be capped by the minimum of the two values defined above.
+    const size_t upperLimit = std::min(maximumSizeBytes, limitToProcessSizeInBytes);
+
+    if (requestedSizeBytes > upperLimit) {
+        requestedSizeBytes = upperLimit;
+    }
+    return requestedSizeBytes;
+}
+}  // namespace mongo::memory_util