Memory: clean up interface used to get memory (RAM) size

src/libcalamares/utils/CalamaresUtilsSystem.cpp

@@ -230,14 +230,7 @@ System::targetEnvOutput( const QString& command,
 }
 
 
-qint64
-System::getPhysicalMemoryB()
-{
-    return 0;
-}
-
-
-qint64
+QPair<quint64, float>
 System::getTotalMemoryB()
 {
 #ifdef Q_OS_LINUX
@@ -245,20 +238,21 @@ System::getTotalMemoryB()
     int r = sysinfo( &i );
 
     if (r)
-        return 0;
+        return qMakePair(0, 0.0);
 
-    return qint64( i.mem_unit ) * i.totalram;
+    return qMakePair(quint64( i.mem_unit ) * quint64( i.totalram ), 1.1);
 #elif defined( Q_OS_FREEBSD )
     unsigned long memsize;
     size_t s = sizeof(memsize);
 
     int r = sysctlbyname("vm.kmem_size", &memsize, &s, NULL, 0);
     if (r)
-        return 0;
+        return qMakePair(0, 0.0);
 
-    return memsize;
+    return qMakePair(memsize, 1.01);
+#else
+    return qMakePair(0, 0.0);  // Unsupported
 #endif
-    return 0;  // Unsupported
 }
 
 

src/libcalamares/utils/CalamaresUtilsSystem.h

@@ -100,9 +100,19 @@ public:
 
     /**
      * @brief getTotalMemoryB returns the total main memory, in bytes.
+     *
+     * Since it is difficult to get the RAM memory size exactly -- either
+     * by reading information from the DIMMs, which may fail on virtual hosts
+     * or from asking the kernel, which doesn't report some memory areas --
+     * this returns a pair of guessed-size (in bytes) and a "guesstimate factor"
+     * which says how good the guess is. Generally, assume the *real* memory
+     * available is size * guesstimate.
+     *
+     * If nothing can be found, returns a 0 size and 0 guesstimate.
+     *
+     * @return size, guesstimate-factor
      */
-    DLLEXPORT qint64 getTotalMemoryB();     //Always underguessed, but always works on Linux
-    DLLEXPORT qint64 getPhysicalMemoryB();  //Better guess, doesn't work in VirualBox
+    DLLEXPORT QPair<quint64, float> getTotalMemoryB();
 
 private:
     static System* s_instance;

src/modules/partition/core/PartitionActions.cpp

@@ -59,19 +59,21 @@ constexpr qint64 toGiB( unsigned long long m )
 qint64
 swapSuggestion( const qint64 availableSpaceB )
 {
-    // swap(mem) = max(2, 2 * mem), if mem < 2 GiB
-    //           = mem,             if 2 GiB <= mem < 8 GiB
-    //           = mem / 2,         if 8 GIB <= mem < 64 GiB
-    //           = 4 GiB,           if mem >= 64 GiB
-
+    /* If suspend-to-disk is demanded, then we always need enough
+     * swap to write the whole memory to disk -- between 2GB and 8GB
+     * RAM give proportionally more swap, and from 8GB RAM keep
+     * swap = RAM.
+     *
+     * If suspend-to-disk is not demanded, then ramp up more slowly,
+     * to 8GB swap at 16GB memory, and then drop to 4GB for "large
+     * memory" machines, on the assumption that those don't need swap
+     * because they have tons of memory (or whatever they are doing,
+     * had better not run into swap).
+     */
     qint64 suggestedSwapSizeB = 0;
-    qint64 availableRamB = CalamaresUtils::System::instance()->getPhysicalMemoryB();
-    qreal overestimationFactor = 1.01;
-    if ( !availableRamB )
-    {
-        availableRamB = CalamaresUtils::System::instance()->getTotalMemoryB();
-        overestimationFactor = 1.10;
-    }
+    auto memory = CalamaresUtils::System::instance()->getTotalMemoryB();
+    qint64 availableRamB = memory.first;
+    qreal overestimationFactor = memory.second;
 
     bool ensureSuspendToDisk =
         Calamares::JobQueue::instance()->globalStorage()->
@@ -94,8 +96,8 @@ swapSuggestion( const qint64 availableSpaceB )
             suggestedSwapSizeB = qMax( 2_GiB, availableRamB * 2 );
         else if ( availableRamB >= 2_GiB && availableRamB < 8_GiB )
             suggestedSwapSizeB = availableRamB;
-        else if ( availableRamB >= 8_GiB && availableRamB < 64_GiB )
-            suggestedSwapSizeB = availableRamB / 2;
+        else if ( availableRamB >= 8_GiB && availableRamB < 16_GiB )
+            suggestedSwapSizeB = 8_GiB;
         else
             suggestedSwapSizeB = 4_GiB;
 

src/modules/welcome/checker/RequirementsChecker.cpp

@@ -307,9 +307,9 @@ RequirementsChecker::checkEnoughStorage( qint64 requiredSpace )
 bool
 RequirementsChecker::checkEnoughRam( qint64 requiredRam )
 {
-    qint64 availableRam = CalamaresUtils::System::instance()->getPhysicalMemoryB();
-    if ( !availableRam )
-        availableRam = CalamaresUtils::System::instance()->getTotalMemoryB();
+    // Ignore the guesstimate-factor; we get an under-estimate
+    // which is probably the usable RAM for programs.
+    quint64 availableRam = CalamaresUtils::System::instance()->getTotalMemoryB().first;
     return availableRam >= requiredRam * 0.95; // because MemTotal is variable
 }