Linux: implement zswap support

On Linux, use zswap to populate "compressed memory" metrics added in the
previous commit.

Fixes #104.

Makefile.am

@@ -173,6 +173,7 @@ linux_platform_headers = \
 	linux/SystemdMeter.h \
 	linux/ZramMeter.h \
 	linux/ZramStats.h \
+	linux/ZswapStats.h \
 	zfs/ZfsArcMeter.h \
 	zfs/ZfsArcStats.h \
 	zfs/ZfsCompressedArcMeter.h

linux/LinuxProcessList.c

@@ -1733,6 +1733,7 @@ errorReadingProcess:
 }
 
 static inline void LinuxProcessList_scanMemoryInfo(ProcessList* this) {
+   LinuxProcessList *lpl = (LinuxProcessList *)this;
    memory_t availableMem = 0;
    memory_t freeMem = 0;
    memory_t totalMem = 0;
@@ -1743,6 +1744,8 @@ static inline void LinuxProcessList_scanMemoryInfo(ProcessList* this) {
    memory_t swapCacheMem = 0;
    memory_t swapFreeMem = 0;
    memory_t sreclaimableMem = 0;
+   memory_t zswapCompMem = 0;
+   memory_t zswapOrigMem = 0;
 
    FILE* file = fopen(PROCMEMINFOFILE, "r");
    if (!file)
@@ -1787,6 +1790,10 @@ static inline void LinuxProcessList_scanMemoryInfo(ProcessList* this) {
             break;
          }
          break;
+      case 'Z':
+         tryRead("Zswap:", zswapCompMem);
+         tryRead("Zswapped:", zswapOrigMem);
+         break;
       }
 
       #undef tryRead
@@ -1812,6 +1819,8 @@ static inline void LinuxProcessList_scanMemoryInfo(ProcessList* this) {
    this->totalSwap = swapTotalMem;
    this->usedSwap = swapTotalMem - swapFreeMem - swapCacheMem;
    this->cachedSwap = swapCacheMem;
+   lpl->zswap.usedZswapComp = zswapCompMem;
+   lpl->zswap.usedZswapOrig = zswapOrigMem;
 }
 
 static void LinuxProcessList_scanHugePages(LinuxProcessList* this) {
@@ -1870,6 +1879,24 @@ static void LinuxProcessList_scanHugePages(LinuxProcessList* this) {
    closedir(dir);
 }
 
+static inline void LinuxProcessList_scanZswapInfo(LinuxProcessList *this) {
+   long max_pool_percent = 0;
+   int r;
+   char buf[256];
+
+   r = xReadfile("/sys/module/zswap/parameters/max_pool_percent", buf, 256);
+   if (r <= 0) {
+      return;
+   }
+   max_pool_percent = strtol(buf, NULL, 10);
+   if (max_pool_percent < 0 || max_pool_percent > 100) {
+      return;
+   }
+
+   this->zswap.totalZswapPool = this->super.totalMem * max_pool_percent / 100;
+   /* the rest of the metrics are set in LinuxProcessList_scanMemoryInfo() */
+}
+
 static inline void LinuxProcessList_scanZramInfo(LinuxProcessList* this) {
    memory_t totalZram = 0;
    memory_t usedZramComp = 0;
@@ -2222,6 +2249,7 @@ void ProcessList_goThroughEntries(ProcessList* super, bool pauseProcessUpdate) {
    LinuxProcessList_scanHugePages(this);
    LinuxProcessList_scanZfsArcstats(this);
    LinuxProcessList_scanZramInfo(this);
+   LinuxProcessList_scanZswapInfo(this);
 
    double period = LinuxProcessList_scanCPUTime(super);
 

linux/LinuxProcessList.h

@@ -16,6 +16,7 @@ in the source distribution for its full text.
 #include "ProcessList.h"
 #include "UsersTable.h"
 #include "linux/ZramStats.h"
+#include "linux/ZswapStats.h"
 #include "zfs/ZfsArcStats.h"
 
 #define HTOP_HUGEPAGE_BASE_SHIFT 16
@@ -85,6 +86,7 @@ typedef struct LinuxProcessList_ {
 
    ZfsArcStats zfs;
    ZramStats zram;
+   ZswapStats zswap;
 } LinuxProcessList;
 
 #ifndef PROCDIR

linux/Platform.c

@@ -359,7 +359,7 @@ void Platform_setMemoryValues(Meter* this) {
    this->values[MEMORY_METER_USED] = pl->usedMem;
    this->values[MEMORY_METER_BUFFERS] = pl->buffersMem;
    this->values[MEMORY_METER_SHARED] = pl->sharedMem;
-   // this->values[MEMORY_METER_COMPRESSED] = "compressed memory, like zswap on linux"
+   this->values[MEMORY_METER_COMPRESSED] = 0; /* compressed */
    this->values[MEMORY_METER_CACHE] = pl->cachedMem;
    this->values[MEMORY_METER_AVAILABLE] = pl->availableMem;
 
@@ -372,13 +372,26 @@ void Platform_setMemoryValues(Meter* this) {
       this->values[MEMORY_METER_CACHE] += shrinkableSize;
       this->values[MEMORY_METER_AVAILABLE] += shrinkableSize;
    }
+
+   if (lpl->zswap.usedZswapOrig > 0 || lpl->zswap.usedZswapComp > 0) {
+      this->values[MEMORY_METER_USED] -= lpl->zswap.usedZswapComp;
+      this->values[MEMORY_METER_COMPRESSED] += lpl->zswap.usedZswapComp;
+   }
 }
 
 void Platform_setSwapValues(Meter* this) {
    const ProcessList* pl = this->pl;
+   const LinuxProcessList* lpl = (const LinuxProcessList*) pl;
+
    this->total = pl->totalSwap;
    this->values[SWAP_METER_USED] = pl->usedSwap;
    this->values[SWAP_METER_CACHE] = pl->cachedSwap;
+   this->values[SWAP_METER_FRONTSWAP] = 0; /* frontswap -- memory that is accounted to swap but resides elsewhere */
+
+   if (lpl->zswap.usedZswapOrig > 0 || lpl->zswap.usedZswapComp > 0) {
+      this->values[SWAP_METER_USED] -= lpl->zswap.usedZswapOrig;
+      this->values[SWAP_METER_FRONTSWAP] += lpl->zswap.usedZswapOrig;
+   }
 }
 
 void Platform_setZramValues(Meter* this) {

linux/ZswapStats.h

@@ -0,0 +1,21 @@
+#ifndef HEADER_ZswapStats
+#define HEADER_ZswapStats
+/*
+htop - ZswapStats.h
+(C) 2022 htop dev team
+Released under the GNU GPLv2+, see the COPYING file
+in the source distribution for its full text.
+*/
+
+#include "ProcessList.h"
+
+typedef struct ZswapStats_ {
+   /* maximum size of the zswap pool */
+   memory_t totalZswapPool;
+   /* amount of RAM used by the zswap pool */
+   memory_t usedZswapComp;
+   /* amount of data stored inside the zswap pool */
+   memory_t usedZswapOrig;
+} ZswapStats;
+
+#endif