diff --git a/executor/prepared_test.go b/executor/prepared_test.go
index 1e56b37ee94e9..57d2a2a791a55 100644
--- a/executor/prepared_test.go
+++ b/executor/prepared_test.go
@@ -23,7 +23,6 @@ import (
 	"github.com/pingcap/tidb/executor"
 	"github.com/pingcap/tidb/metrics"
 	plannercore "github.com/pingcap/tidb/planner/core"
-	"github.com/pingcap/tidb/util/memory"
 	"github.com/pingcap/tidb/util/testkit"
 	dto "github.com/prometheus/client_model/go"
 	"golang.org/x/net/context"
@@ -47,8 +46,9 @@ func (s *testSuite) TestPrepared(c *C) {
 		plannercore.SetPreparedPlanCache(flag)
 		plannercore.PreparedPlanCacheCapacity = 100
 		plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-		plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-		c.Assert(err, IsNil)
+		// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+		// behavior would not be effected by the uncertain memory utilization.
+		plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 		tk := testkit.NewTestKit(c, s.store)
 		tk.MustExec("use test")
 		tk.MustExec("drop table if exists prepare_test")
@@ -253,8 +253,9 @@ func (s *testSuite) TestPreparedLimitOffset(c *C) {
 		plannercore.SetPreparedPlanCache(flag)
 		plannercore.PreparedPlanCacheCapacity = 100
 		plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-		plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-		c.Assert(err, IsNil)
+		// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+		// behavior would not be effected by the uncertain memory utilization.
+		plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 		tk := testkit.NewTestKit(c, s.store)
 		tk.MustExec("use test")
 		tk.MustExec("drop table if exists prepare_test")
@@ -292,12 +293,12 @@ func (s *testSuite) TestPreparedNullParam(c *C) {
 	}()
 	flags := []bool{false, true}
 	for _, flag := range flags {
-		var err error
 		plannercore.SetPreparedPlanCache(flag)
 		plannercore.PreparedPlanCacheCapacity = 100
 		plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-		plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-		c.Assert(err, IsNil)
+		// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+		// behavior would not be effected by the uncertain memory utilization.
+		plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 		tk := testkit.NewTestKit(c, s.store)
 		tk.MustExec("use test")
 		tk.MustExec("drop table if exists t")
@@ -364,12 +365,12 @@ func (s *testSuite) TestPrepareWithAggregation(c *C) {
 	}()
 	flags := []bool{false, true}
 	for _, flag := range flags {
-		var err error
 		plannercore.SetPreparedPlanCache(flag)
 		plannercore.PreparedPlanCacheCapacity = 100
 		plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-		plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-		c.Assert(err, IsNil)
+		// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+		// behavior would not be effected by the uncertain memory utilization.
+		plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 		tk := testkit.NewTestKit(c, s.store)
 		tk.MustExec("use test")
 		tk.MustExec("drop table if exists t")
@@ -409,12 +410,12 @@ func (s *testSuite) TestPreparedIssue7579(c *C) {
 	}()
 	flags := []bool{false, true}
 	for _, flag := range flags {
-		var err error
 		plannercore.SetPreparedPlanCache(flag)
 		plannercore.PreparedPlanCacheCapacity = 100
 		plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-		plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-		c.Assert(err, IsNil)
+		// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+		// behavior would not be effected by the uncertain memory utilization.
+		plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 		tk := testkit.NewTestKit(c, s.store)
 		tk.MustExec("use test")
 		tk.MustExec("drop table if exists t")
@@ -463,12 +464,12 @@ func (s *testSuite) TestPreparedInsert(c *C) {
 	pb := &dto.Metric{}
 	flags := []bool{false, true}
 	for _, flag := range flags {
-		var err error
 		plannercore.SetPreparedPlanCache(flag)
 		plannercore.PreparedPlanCacheCapacity = 100
 		plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-		plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-		c.Assert(err, IsNil)
+		// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+		// behavior would not be effected by the uncertain memory utilization.
+		plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 		tk := testkit.NewTestKit(c, s.store)
 		tk.MustExec("use test")
 		tk.MustExec("drop table if exists prepare_test")
@@ -545,12 +546,12 @@ func (s *testSuite) TestPreparedUpdate(c *C) {
 	pb := &dto.Metric{}
 	flags := []bool{false, true}
 	for _, flag := range flags {
-		var err error
 		plannercore.SetPreparedPlanCache(flag)
 		plannercore.PreparedPlanCacheCapacity = 100
 		plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-		plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-		c.Assert(err, IsNil)
+		// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+		// behavior would not be effected by the uncertain memory utilization.
+		plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 		tk := testkit.NewTestKit(c, s.store)
 		tk.MustExec("use test")
 		tk.MustExec("drop table if exists prepare_test")
@@ -604,12 +605,12 @@ func (s *testSuite) TestPreparedDelete(c *C) {
 	pb := &dto.Metric{}
 	flags := []bool{false, true}
 	for _, flag := range flags {
-		var err error
 		plannercore.SetPreparedPlanCache(flag)
 		plannercore.PreparedPlanCacheCapacity = 100
 		plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-		plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-		c.Assert(err, IsNil)
+		// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+		// behavior would not be effected by the uncertain memory utilization.
+		plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 		tk := testkit.NewTestKit(c, s.store)
 		tk.MustExec("use test")
 		tk.MustExec("drop table if exists prepare_test")
@@ -658,12 +659,12 @@ func (s *testSuite) TestPrepareDealloc(c *C) {
 		plannercore.PreparedPlanCacheMemoryGuardRatio = orgMemGuardRatio
 		plannercore.PreparedPlanCacheMaxMemory = orgMaxMemory
 	}()
-	var err error
 	plannercore.SetPreparedPlanCache(true)
 	plannercore.PreparedPlanCacheCapacity = 3
 	plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-	plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-	c.Assert(err, IsNil)
+	// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+	// behavior would not be effected by the uncertain memory utilization.
+	plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")
@@ -706,7 +707,9 @@ func (s *testSuite) TestPreparedIssue8153(c *C) {
 		plannercore.SetPreparedPlanCache(flag)
 		plannercore.PreparedPlanCacheCapacity = 100
 		plannercore.PreparedPlanCacheMemoryGuardRatio = 0.1
-		plannercore.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
+		// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+		// behavior would not be effected by the uncertain memory utilization.
+		plannercore.PreparedPlanCacheMaxMemory = math.MaxUint64
 		tk := testkit.NewTestKit(c, s.store)
 		tk.MustExec("use test")
 		tk.MustExec("drop table if exists t")
diff --git a/planner/core/point_get_plan_test.go b/planner/core/point_get_plan_test.go
index be81fff292802..a485bd488aac8 100644
--- a/planner/core/point_get_plan_test.go
+++ b/planner/core/point_get_plan_test.go
@@ -14,10 +14,11 @@
 package core_test
 
 import (
+	"math"
+
 	. "github.com/pingcap/check"
 	"github.com/pingcap/tidb/metrics"
 	"github.com/pingcap/tidb/planner/core"
-	"github.com/pingcap/tidb/util/memory"
 	"github.com/pingcap/tidb/util/testkit"
 	"github.com/pingcap/tidb/util/testleak"
 	dto "github.com/prometheus/client_model/go"
@@ -48,8 +49,9 @@ func (s *testPointGetSuite) TestPointGetPlanCache(c *C) {
 	core.SetPreparedPlanCache(true)
 	core.PreparedPlanCacheCapacity = 100
 	core.PreparedPlanCacheMemoryGuardRatio = 0.1
-	core.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-	c.Assert(err, IsNil)
+	// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+	// behavior would not be effected by the uncertain memory utilization.
+	core.PreparedPlanCacheMaxMemory = math.MaxUint64
 	tk.MustExec("use test")
 	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t(a int primary key, b int, c int, key idx_bc(b,c))")
diff --git a/planner/core/prepare_test.go b/planner/core/prepare_test.go
index 38f914870fe6b..795b563bfd5aa 100644
--- a/planner/core/prepare_test.go
+++ b/planner/core/prepare_test.go
@@ -14,6 +14,7 @@
 package core_test
 
 import (
+	"math"
 	"strconv"
 	"time"
 
@@ -24,7 +25,6 @@ import (
 	"github.com/pingcap/tidb/metrics"
 	"github.com/pingcap/tidb/planner/core"
 	"github.com/pingcap/tidb/sessionctx/variable"
-	"github.com/pingcap/tidb/util/memory"
 	"github.com/pingcap/tidb/util/testkit"
 	"github.com/pingcap/tidb/util/testleak"
 	"github.com/prometheus/client_golang/prometheus"
@@ -56,8 +56,9 @@ func (s *testPrepareSuite) TestPrepareCache(c *C) {
 	core.SetPreparedPlanCache(true)
 	core.PreparedPlanCacheCapacity = 100
 	core.PreparedPlanCacheMemoryGuardRatio = 0.1
-	core.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-	c.Assert(err, IsNil)
+	// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+	// behavior would not be effected by the uncertain memory utilization.
+	core.PreparedPlanCacheMaxMemory = math.MaxUint64
 	tk.MustExec("use test")
 	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t(a int primary key, b int, c int, index idx1(b, a), index idx2(b))")
@@ -105,8 +106,9 @@ func (s *testPrepareSuite) TestPrepareCacheIndexScan(c *C) {
 	core.SetPreparedPlanCache(true)
 	core.PreparedPlanCacheCapacity = 100
 	core.PreparedPlanCacheMemoryGuardRatio = 0.1
-	core.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-	c.Assert(err, IsNil)
+	// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+	// behavior would not be effected by the uncertain memory utilization.
+	core.PreparedPlanCacheMaxMemory = math.MaxUint64
 	tk.MustExec("use test")
 	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t(a int, b int, c int, primary key (a, b))")
@@ -138,8 +140,9 @@ func (s *testPlanSuite) TestPrepareCacheDeferredFunction(c *C) {
 	core.SetPreparedPlanCache(true)
 	core.PreparedPlanCacheCapacity = 100
 	core.PreparedPlanCacheMemoryGuardRatio = 0.1
-	core.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-	c.Assert(err, IsNil)
+	// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+	// behavior would not be effected by the uncertain memory utilization.
+	core.PreparedPlanCacheMaxMemory = math.MaxUint64
 
 	defer testleak.AfterTest(c)()
 
@@ -198,8 +201,9 @@ func (s *testPrepareSuite) TestPrepareCacheNow(c *C) {
 	core.SetPreparedPlanCache(true)
 	core.PreparedPlanCacheCapacity = 100
 	core.PreparedPlanCacheMemoryGuardRatio = 0.1
-	core.PreparedPlanCacheMaxMemory, err = memory.MemTotal()
-	c.Assert(err, IsNil)
+	// PreparedPlanCacheMaxMemory is set to MAX_UINT64 to make sure the cache
+	// behavior would not be effected by the uncertain memory utilization.
+	core.PreparedPlanCacheMaxMemory = math.MaxUint64
 	tk.MustExec("use test")
 	tk.MustExec(`prepare stmt1 from "select now(), sleep(1), now()"`)
 	// When executing one statement at the first time, we don't use cache, so we need to execute it at least twice to test the cache.