diff --git a/libmeminfo/Android.bp b/libmeminfo/Android.bp
index aab3743..3e191ad 100644
--- a/libmeminfo/Android.bp
+++ b/libmeminfo/Android.bp
@@ -54,6 +54,11 @@
     srcs: [
         "libmeminfo_test.cpp"
     ],
+
+    data: [
+        "testdata1/*",
+        "testdata2/*"
+    ],
 }
 
 cc_benchmark {
@@ -67,4 +72,8 @@
         "libmeminfo",
         "libprocinfo",
     ],
+
+    data: [
+        "testdata1/*",
+    ],
 }
diff --git a/libmeminfo/include/meminfo/meminfo.h b/libmeminfo/include/meminfo/meminfo.h
index c328648..809054b 100644
--- a/libmeminfo/include/meminfo/meminfo.h
+++ b/libmeminfo/include/meminfo/meminfo.h
@@ -31,6 +31,8 @@
     uint64_t pss;
     uint64_t uss;
 
+    uint64_t swap;
+
     uint64_t private_clean;
     uint64_t private_dirty;
     uint64_t shared_clean;
@@ -41,6 +43,7 @@
           rss(0),
           pss(0),
           uss(0),
+          swap(0),
           private_clean(0),
           private_dirty(0),
           shared_clean(0),
@@ -49,7 +52,7 @@
     ~MemUsage() = default;
 
     void clear() {
-        vss = rss = pss = uss = 0;
+        vss = rss = pss = uss = swap = 0;
         private_clean = private_dirty = shared_clean = shared_dirty = 0;
     }
 };
diff --git a/libmeminfo/include/meminfo/procmeminfo.h b/libmeminfo/include/meminfo/procmeminfo.h
index b37c56b..92375d3 100644
--- a/libmeminfo/include/meminfo/procmeminfo.h
+++ b/libmeminfo/include/meminfo/procmeminfo.h
@@ -29,13 +29,16 @@
 class ProcMemInfo final {
     // Per-process memory accounting
   public:
-    ProcMemInfo(pid_t pid, bool get_wss = false);
+    // Reset the working set accounting of the process via /proc/<pid>/clear_refs
+    static bool ResetWorkingSet(pid_t pid);
+
+    ProcMemInfo(pid_t pid, bool get_wss = false, uint64_t pgflags = 0, uint64_t pgflags_mask = 0);
 
     const std::vector<Vma>& Maps();
     const MemUsage& Usage();
     const MemUsage& Wss();
+    const std::vector<uint16_t>& SwapOffsets();
 
-    bool WssReset();
     ~ProcMemInfo() = default;
 
   private:
@@ -44,11 +47,14 @@
 
     pid_t pid_;
     bool get_wss_;
+    uint64_t pgflags_;
+    uint64_t pgflags_mask_;
 
     std::vector<Vma> maps_;
 
     MemUsage usage_;
     MemUsage wss_;
+    std::vector<uint16_t> swap_offsets_;
 };
 
 }  // namespace meminfo
diff --git a/libmeminfo/include/meminfo/sysmeminfo.h b/libmeminfo/include/meminfo/sysmeminfo.h
index f5e05bd..885be1d 100644
--- a/libmeminfo/include/meminfo/sysmeminfo.h
+++ b/libmeminfo/include/meminfo/sysmeminfo.h
@@ -28,6 +28,21 @@
 class SysMemInfo final {
     // System or Global memory accounting
   public:
+    static constexpr const char* kMemTotal = "MemTotal:";
+    static constexpr const char* kMemFree = "MemFree:";
+    static constexpr const char* kMemBuffers = "Buffers:";
+    static constexpr const char* kMemCached = "Cached:";
+    static constexpr const char* kMemShmem = "Shmem:";
+    static constexpr const char* kMemSlab = "Slab:";
+    static constexpr const char* kMemSReclaim = "SReclaimable:";
+    static constexpr const char* kMemSUnreclaim = "SUnreclaim:";
+    static constexpr const char* kMemSwapTotal = "SwapTotal:";
+    static constexpr const char* kMemSwapFree = "SwapFree:";
+    static constexpr const char* kMemMapped = "Mapped:";
+    static constexpr const char* kMemVmallocUsed = "VmallocUsed:";
+    static constexpr const char* kMemPageTables = "PageTables:";
+    static constexpr const char* kMemKernelStack = "KernelStack:";
+
     static const std::vector<std::string> kDefaultSysMemInfoTags;
 
     SysMemInfo() = default;
@@ -38,24 +53,25 @@
                      const std::string& path = "/proc/meminfo");
 
     // getters
-    uint64_t mem_total_kb() { return mem_in_kb_["MemTotal:"]; }
-    uint64_t mem_free_kb() { return mem_in_kb_["MemFree:"]; }
-    uint64_t mem_buffers_kb() { return mem_in_kb_["Buffers:"]; }
-    uint64_t mem_cached_kb() { return mem_in_kb_["Cached:"]; }
-    uint64_t mem_shmem_kb() { return mem_in_kb_["Shmem:"]; }
-    uint64_t mem_slab_kb() { return mem_in_kb_["Slab:"]; }
-    uint64_t mem_slab_reclailmable_kb() { return mem_in_kb_["SReclaimable:"]; }
-    uint64_t mem_slab_unreclaimable_kb() { return mem_in_kb_["SUnreclaim:"]; }
-    uint64_t mem_swap_kb() { return mem_in_kb_["SwapTotal:"]; }
-    uint64_t mem_free_swap_kb() { return mem_in_kb_["SwapFree:"]; }
-    uint64_t mem_zram_kb() { return mem_in_kb_["Zram:"]; }
-    uint64_t mem_mapped_kb() { return mem_in_kb_["Mapped:"]; }
-    uint64_t mem_vmalloc_used_kb() { return mem_in_kb_["VmallocUsed:"]; }
-    uint64_t mem_page_tables_kb() { return mem_in_kb_["PageTables:"]; }
-    uint64_t mem_kernel_stack_kb() { return mem_in_kb_["KernelStack:"]; }
+    uint64_t mem_total_kb() { return mem_in_kb_[kMemTotal]; }
+    uint64_t mem_free_kb() { return mem_in_kb_[kMemFree]; }
+    uint64_t mem_buffers_kb() { return mem_in_kb_[kMemBuffers]; }
+    uint64_t mem_cached_kb() { return mem_in_kb_[kMemCached]; }
+    uint64_t mem_shmem_kb() { return mem_in_kb_[kMemShmem]; }
+    uint64_t mem_slab_kb() { return mem_in_kb_[kMemSlab]; }
+    uint64_t mem_slab_reclailmable_kb() { return mem_in_kb_[kMemSReclaim]; }
+    uint64_t mem_slab_unreclaimable_kb() { return mem_in_kb_[kMemSUnreclaim]; }
+    uint64_t mem_swap_kb() { return mem_in_kb_[kMemSwapTotal]; }
+    uint64_t mem_swap_free_kb() { return mem_in_kb_[kMemSwapFree]; }
+    uint64_t mem_mapped_kb() { return mem_in_kb_[kMemMapped]; }
+    uint64_t mem_vmalloc_used_kb() { return mem_in_kb_[kMemVmallocUsed]; }
+    uint64_t mem_page_tables_kb() { return mem_in_kb_[kMemPageTables]; }
+    uint64_t mem_kernel_stack_kb() { return mem_in_kb_[kMemPageTables]; }
+    uint64_t mem_zram_kb(const std::string& zram_dev = "");
 
   private:
     std::map<std::string, uint64_t> mem_in_kb_;
+    bool MemZramDevice(const std::string& zram_dev, uint64_t* mem_zram_dev);
 };
 
 }  // namespace meminfo
diff --git a/libmeminfo/libmeminfo_benchmark.cpp b/libmeminfo/libmeminfo_benchmark.cpp
index e2239f0..1db0824 100644
--- a/libmeminfo/libmeminfo_benchmark.cpp
+++ b/libmeminfo/libmeminfo_benchmark.cpp
@@ -17,6 +17,8 @@
 #include <meminfo/sysmeminfo.h>
 
 #include <fcntl.h>
+#include <inttypes.h>
+#include <stdio.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 
@@ -46,7 +48,7 @@
     MEMINFO_COUNT
 };
 
-void get_mem_info(uint64_t mem[], const char* file) {
+static void get_mem_info(uint64_t mem[], const char* file) {
     char buffer[4096];
     unsigned int numFound = 0;
 
@@ -67,9 +69,10 @@
     buffer[len] = 0;
 
     static const char* const tags[] = {
-            "MemTotal:",     "MemFree:",    "Buffers:",     "Cached:",       "Shmem:", "Slab:",
-            "SReclaimable:", "SUnreclaim:", "SwapTotal:",   "SwapFree:",     "ZRam:",  "Mapped:",
-            "VmallocUsed:",  "PageTables:", "KernelStack:", NULL};
+            "MemTotal:",     "MemFree:",    "Buffers:",     "Cached:",   "Shmem:", "Slab:",
+            "SReclaimable:", "SUnreclaim:", "SwapTotal:",   "SwapFree:", "ZRam:",  "Mapped:",
+            "VmallocUsed:",  "PageTables:", "KernelStack:", NULL
+    };
 
     static const int tagsLen[] = {9, 8, 8, 7, 6, 5, 13, 11, 10, 9, 5, 7, 12, 11, 12, 0};
 
@@ -78,7 +81,8 @@
     while (*p && (numFound < (sizeof(tagsLen) / sizeof(tagsLen[0])))) {
         int i = 0;
         while (tags[i]) {
-            //std::cout << "tag =" << tags[i] << " p = " << std::string(p, tagsLen[i]) << std::endl;
+            // std::cout << "tag =" << tags[i] << " p = " << std::string(p, tagsLen[i]) <<
+            // std::endl;
             if (strncmp(p, tags[i], tagsLen[i]) == 0) {
                 p += tagsLen[i];
                 while (*p == ' ') p++;
@@ -214,4 +218,51 @@
 }
 BENCHMARK(BM_ReadMemInfo);
 
+static uint64_t get_zram_mem_used(const std::string& zram_dir) {
+    FILE* f = fopen((zram_dir + "mm_stat").c_str(), "r");
+    if (f) {
+        uint64_t mem_used_total = 0;
+
+        int matched = fscanf(f, "%*d %*d %" SCNu64 " %*d %*d %*d %*d", &mem_used_total);
+        if (matched != 1)
+            fprintf(stderr, "warning: failed to parse %s\n", (zram_dir + "mm_stat").c_str());
+
+        fclose(f);
+        return mem_used_total;
+    }
+
+    f = fopen((zram_dir + "mem_used_total").c_str(), "r");
+    if (f) {
+        uint64_t mem_used_total = 0;
+
+        int matched = fscanf(f, "%" SCNu64, &mem_used_total);
+        if (matched != 1)
+            fprintf(stderr, "warning: failed to parse %s\n", (zram_dir + "mem_used_total").c_str());
+
+        fclose(f);
+        return mem_used_total;
+    }
+
+    return 0;
+}
+
+static void BM_OldReadZramTotal(benchmark::State& state) {
+    std::string exec_dir = ::android::base::GetExecutableDirectory();
+    std::string zram_mmstat_dir = exec_dir + "/testdata1/";
+    for (auto _ : state) {
+        uint64_t zram_total __attribute__((unused)) = get_zram_mem_used(zram_mmstat_dir) / 1024;
+    }
+}
+BENCHMARK(BM_OldReadZramTotal);
+
+static void BM_NewReadZramTotal(benchmark::State& state) {
+    std::string exec_dir = ::android::base::GetExecutableDirectory();
+    std::string zram_mmstat_dir = exec_dir + "/testdata1/";
+    ::android::meminfo::SysMemInfo mi;
+    for (auto _ : state) {
+        uint64_t zram_total __attribute__((unused)) = mi.mem_zram_kb(zram_mmstat_dir);
+    }
+}
+BENCHMARK(BM_NewReadZramTotal);
+
 BENCHMARK_MAIN();
diff --git a/libmeminfo/libmeminfo_test.cpp b/libmeminfo/libmeminfo_test.cpp
index 7a2be41..b7a4b6b 100644
--- a/libmeminfo/libmeminfo_test.cpp
+++ b/libmeminfo/libmeminfo_test.cpp
@@ -73,7 +73,7 @@
     }
 }
 
-TEST_F(ValidateProcMemInfo, TestMapsUsage) {
+TEST_F(ValidateProcMemInfo, TestMaps) {
     const std::vector<Vma>& maps = proc_mem->Maps();
     ASSERT_FALSE(maps.empty());
     ASSERT_EQ(proc->num_maps, maps.size());
@@ -96,6 +96,30 @@
     EXPECT_EQ(proc_usage.uss, proc_mem->Usage().uss);
 }
 
+TEST_F(ValidateProcMemInfo, TestSwapUsage) {
+    const std::vector<Vma>& maps = proc_mem->Maps();
+    ASSERT_FALSE(maps.empty());
+    ASSERT_EQ(proc->num_maps, maps.size());
+
+    pm_memusage_t map_usage, proc_usage;
+    pm_memusage_zero(&map_usage);
+    pm_memusage_zero(&proc_usage);
+    for (size_t i = 0; i < maps.size(); i++) {
+        ASSERT_EQ(0, pm_map_usage(proc->maps[i], &map_usage));
+        EXPECT_EQ(map_usage.swap, maps[i].usage.swap) << "SWAP mismatch for map: " << maps[i].name;
+        pm_memusage_add(&proc_usage, &map_usage);
+    }
+
+    EXPECT_EQ(proc_usage.swap, proc_mem->Usage().swap);
+}
+
+TEST_F(ValidateProcMemInfo, TestSwapOffsets) {
+    const MemUsage& proc_usage = proc_mem->Usage();
+    const std::vector<uint16_t>& swap_offsets = proc_mem->SwapOffsets();
+
+    EXPECT_EQ(proc_usage.swap / getpagesize(), swap_offsets.size());
+}
+
 class ValidateProcMemInfoWss : public ::testing::Test {
   protected:
     void SetUp() override {
@@ -118,7 +142,7 @@
 
 TEST_F(ValidateProcMemInfoWss, TestWorkingTestReset) {
     // Expect reset to succeed
-    EXPECT_TRUE(proc_mem->WssReset());
+    EXPECT_TRUE(ProcMemInfo::ResetWorkingSet(pid));
 }
 
 TEST_F(ValidateProcMemInfoWss, TestWssEquality) {
@@ -221,6 +245,93 @@
     }
 }
 
+TEST(TestProcMemInfo, TestMapsEmpty) {
+    ProcMemInfo proc_mem(pid);
+    const std::vector<Vma>& maps = proc_mem.Maps();
+    EXPECT_GT(maps.size(), 0);
+}
+
+TEST(TestProcMemInfo, TestUsageEmpty) {
+    // If we created the object for getting working set,
+    // the usage must be empty
+    ProcMemInfo proc_mem(pid, true);
+    const MemUsage& usage = proc_mem.Usage();
+    EXPECT_EQ(usage.rss, 0);
+    EXPECT_EQ(usage.vss, 0);
+    EXPECT_EQ(usage.pss, 0);
+    EXPECT_EQ(usage.uss, 0);
+    EXPECT_EQ(usage.swap, 0);
+}
+
+TEST(TestProcMemInfoWssReset, TestWssEmpty) {
+    // If we created the object for getting usage,
+    // the working set must be empty
+    ProcMemInfo proc_mem(pid, false);
+    const MemUsage& wss = proc_mem.Wss();
+    EXPECT_EQ(wss.rss, 0);
+    EXPECT_EQ(wss.vss, 0);
+    EXPECT_EQ(wss.pss, 0);
+    EXPECT_EQ(wss.uss, 0);
+    EXPECT_EQ(wss.swap, 0);
+}
+
+TEST(TestProcMemInfoWssReset, TestSwapOffsetsEmpty) {
+    // If we created the object for getting working set,
+    // the swap offsets must be empty
+    ProcMemInfo proc_mem(pid, true);
+    const std::vector<uint16_t>& swap_offsets = proc_mem.SwapOffsets();
+    EXPECT_EQ(swap_offsets.size(), 0);
+}
+
+TEST(ValidateProcMemInfoFlags, TestPageFlags1) {
+    // Create proc object using libpagemap
+    pm_kernel_t* ker;
+    ASSERT_EQ(0, pm_kernel_create(&ker));
+    pm_process_t* proc;
+    ASSERT_EQ(0, pm_process_create(ker, pid, &proc));
+
+    // count swapbacked pages using libpagemap
+    pm_memusage_t proc_usage;
+    pm_memusage_zero(&proc_usage);
+    ASSERT_EQ(0, pm_process_usage_flags(proc, &proc_usage, (1 << KPF_SWAPBACKED),
+                                        (1 << KPF_SWAPBACKED)));
+
+    // Create ProcMemInfo that counts swapbacked pages
+    ProcMemInfo proc_mem(pid, false, (1 << KPF_SWAPBACKED), (1 << KPF_SWAPBACKED));
+
+    EXPECT_EQ(proc_usage.vss, proc_mem.Usage().vss);
+    EXPECT_EQ(proc_usage.rss, proc_mem.Usage().rss);
+    EXPECT_EQ(proc_usage.pss, proc_mem.Usage().pss);
+    EXPECT_EQ(proc_usage.uss, proc_mem.Usage().uss);
+
+    pm_process_destroy(proc);
+    pm_kernel_destroy(ker);
+}
+
+TEST(ValidateProcMemInfoFlags, TestPageFlags2) {
+    // Create proc object using libpagemap
+    pm_kernel_t* ker;
+    ASSERT_EQ(0, pm_kernel_create(&ker));
+    pm_process_t* proc;
+    ASSERT_EQ(0, pm_process_create(ker, pid, &proc));
+
+    // count non-swapbacked pages using libpagemap
+    pm_memusage_t proc_usage;
+    pm_memusage_zero(&proc_usage);
+    ASSERT_EQ(0, pm_process_usage_flags(proc, &proc_usage, (1 << KPF_SWAPBACKED), 0));
+
+    // Create ProcMemInfo that counts non-swapbacked pages
+    ProcMemInfo proc_mem(pid, false, 0, (1 << KPF_SWAPBACKED));
+
+    EXPECT_EQ(proc_usage.vss, proc_mem.Usage().vss);
+    EXPECT_EQ(proc_usage.rss, proc_mem.Usage().rss);
+    EXPECT_EQ(proc_usage.pss, proc_mem.Usage().pss);
+    EXPECT_EQ(proc_usage.uss, proc_mem.Usage().uss);
+
+    pm_process_destroy(proc);
+    pm_kernel_destroy(ker);
+}
+
 TEST(SysMemInfoParser, TestSysMemInfoFile) {
     std::string meminfo = R"meminfo(MemTotal:        3019740 kB
 MemFree:         1809728 kB
@@ -288,6 +399,17 @@
     EXPECT_EQ(mi.mem_total_kb(), 0);
 }
 
+TEST(SysMemInfoParse, TestZramTotal) {
+    std::string exec_dir = ::android::base::GetExecutableDirectory();
+
+    SysMemInfo mi;
+    std::string zram_mmstat_dir = exec_dir + "/testdata1/";
+    EXPECT_EQ(mi.mem_zram_kb(zram_mmstat_dir), 30504);
+
+    std::string zram_memused_dir = exec_dir + "/testdata2/";
+    EXPECT_EQ(mi.mem_zram_kb(zram_memused_dir), 30504);
+}
+
 int main(int argc, char** argv) {
     ::testing::InitGoogleTest(&argc, argv);
     if (argc <= 1) {
diff --git a/libmeminfo/procmeminfo.cpp b/libmeminfo/procmeminfo.cpp
index fe91d25..8867e14 100644
--- a/libmeminfo/procmeminfo.cpp
+++ b/libmeminfo/procmeminfo.cpp
@@ -44,6 +44,8 @@
     to->pss += from.pss;
     to->uss += from.uss;
 
+    to->swap += from.swap;
+
     to->private_clean += from.private_clean;
     to->private_dirty += from.private_dirty;
 
@@ -51,48 +53,78 @@
     to->shared_dirty += from.shared_dirty;
 }
 
-ProcMemInfo::ProcMemInfo(pid_t pid, bool get_wss) : pid_(pid), get_wss_(get_wss) {
-    if (!ReadMaps(get_wss_)) {
-        LOG(ERROR) << "Failed to read maps for Process " << pid_;
-    }
-}
-
-const std::vector<Vma>& ProcMemInfo::Maps() {
-    return maps_;
-}
-
-const MemUsage& ProcMemInfo::Usage() {
-    if (get_wss_) {
-        LOG(WARNING) << "Trying to read memory usage from working set object";
-    }
-    return usage_;
-}
-
-const MemUsage& ProcMemInfo::Wss() {
-    if (!get_wss_) {
-        LOG(WARNING) << "Trying to read working set when there is none";
-    }
-
-    return wss_;
-}
-
-bool ProcMemInfo::WssReset() {
-    if (!get_wss_) {
-        LOG(ERROR) << "Trying to reset working set from a memory usage counting object";
-        return false;
-    }
-
-    std::string clear_refs_path = ::android::base::StringPrintf("/proc/%d/clear_refs", pid_);
+bool ProcMemInfo::ResetWorkingSet(pid_t pid) {
+    std::string clear_refs_path = ::android::base::StringPrintf("/proc/%d/clear_refs", pid);
     if (!::android::base::WriteStringToFile("1\n", clear_refs_path)) {
         PLOG(ERROR) << "Failed to write to " << clear_refs_path;
         return false;
     }
 
-    wss_.clear();
     return true;
 }
 
+ProcMemInfo::ProcMemInfo(pid_t pid, bool get_wss, uint64_t pgflags, uint64_t pgflags_mask)
+    : pid_(pid), get_wss_(get_wss), pgflags_(pgflags), pgflags_mask_(pgflags_mask) {}
+
+const std::vector<Vma>& ProcMemInfo::Maps() {
+    if (maps_.empty() && !ReadMaps(get_wss_)) {
+        LOG(ERROR) << "Failed to read maps for Process " << pid_;
+    }
+
+    return maps_;
+}
+
+const MemUsage& ProcMemInfo::Usage() {
+    if (get_wss_) {
+        LOG(WARNING) << "Trying to read process memory usage for " << pid_
+                     << " using invalid object";
+        return usage_;
+    }
+
+    if (maps_.empty() && !ReadMaps(get_wss_)) {
+        LOG(ERROR) << "Failed to get memory usage for Process " << pid_;
+    }
+
+    return usage_;
+}
+
+const MemUsage& ProcMemInfo::Wss() {
+    if (!get_wss_) {
+        LOG(WARNING) << "Trying to read process working set for " << pid_
+                     << " using invalid object";
+        return wss_;
+    }
+
+    if (maps_.empty() && !ReadMaps(get_wss_)) {
+        LOG(ERROR) << "Failed to get working set for Process " << pid_;
+    }
+
+    return wss_;
+}
+
+const std::vector<uint16_t>& ProcMemInfo::SwapOffsets() {
+    if (get_wss_) {
+        LOG(WARNING) << "Trying to read process swap offsets for " << pid_
+                     << " using invalid object";
+        return swap_offsets_;
+    }
+
+    if (maps_.empty() && !ReadMaps(get_wss_)) {
+        LOG(ERROR) << "Failed to get swap offsets for Process " << pid_;
+    }
+
+    return swap_offsets_;
+}
+
 bool ProcMemInfo::ReadMaps(bool get_wss) {
+    // Each object reads /proc/<pid>/maps only once. This is done to make sure programs that are
+    // running for the lifetime of the system can recycle the objects and don't have to
+    // unnecessarily retain and update this object in memory (which can get significantly large).
+    // E.g. A program that only needs to reset the working set will never all ->Maps(), ->Usage().
+    // E.g. A program that is monitoring smaps_rollup, may never call ->maps(), Usage(), so it
+    // doesn't make sense for us to parse and retain unnecessary memory accounting stats by default.
+    if (!maps_.empty()) return true;
+
     // parse and read /proc/<pid>/maps
     std::string maps_file = ::android::base::StringPrintf("/proc/%d/maps", pid_);
     if (!::android::procinfo::ReadMapFile(
@@ -115,8 +147,8 @@
 
     for (auto& vma : maps_) {
         if (!ReadVmaStats(pagemap_fd.get(), vma, get_wss)) {
-            LOG(ERROR) << "Failed to read page map for vma " << vma.name << "[" << vma.start
-                       << "-" << vma.end << "]";
+            LOG(ERROR) << "Failed to read page map for vma " << vma.name << "[" << vma.start << "-"
+                       << vma.end << "]";
             maps_.clear();
             return false;
         }
@@ -153,18 +185,24 @@
         if (!PAGE_PRESENT(p) && !PAGE_SWAPPED(p)) continue;
 
         if (PAGE_SWAPPED(p)) {
-            // TODO: do what's needed for swapped pages
+            vma.usage.swap += pagesz;
+            swap_offsets_.emplace_back(PAGE_SWAP_OFFSET(p));
             continue;
         }
 
         uint64_t page_frame = PAGE_PFN(p);
         if (!pinfo.PageFlags(page_frame, &pg_flags[i])) {
             LOG(ERROR) << "Failed to get page flags for " << page_frame << " in process " << pid_;
+            swap_offsets_.clear();
             return false;
         }
 
+        // skip unwanted pages from the count
+        if ((pg_flags[i] & pgflags_mask_) != pgflags_) continue;
+
         if (!pinfo.PageMapCount(page_frame, &pg_counts[i])) {
             LOG(ERROR) << "Failed to get page count for " << page_frame << " in process " << pid_;
+            swap_offsets_.clear();
             return false;
         }
 
diff --git a/libmeminfo/sysmeminfo.cpp b/libmeminfo/sysmeminfo.cpp
index 50fa213..7e56238 100644
--- a/libmeminfo/sysmeminfo.cpp
+++ b/libmeminfo/sysmeminfo.cpp
@@ -17,10 +17,12 @@
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <inttypes.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 #include <cctype>
+#include <cstdio>
 #include <fstream>
 #include <string>
 #include <utility>
@@ -29,7 +31,9 @@
 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/parseint.h>
+#include <android-base/stringprintf.h>
 #include <android-base/strings.h>
+#include <android-base/unique_fd.h>
 
 #include "meminfo_private.h"
 
@@ -37,9 +41,11 @@
 namespace meminfo {
 
 const std::vector<std::string> SysMemInfo::kDefaultSysMemInfoTags = {
-    "MemTotal:", "MemFree:",      "Buffers:",     "Cached:",     "Shmem:",
-    "Slab:",     "SReclaimable:", "SUnreclaim:",  "SwapTotal:",  "SwapFree:",
-    "ZRam:",     "Mapped:",       "VmallocUsed:", "PageTables:", "KernelStack:",
+        SysMemInfo::kMemTotal,      SysMemInfo::kMemFree,        SysMemInfo::kMemBuffers,
+        SysMemInfo::kMemCached,     SysMemInfo::kMemShmem,       SysMemInfo::kMemSlab,
+        SysMemInfo::kMemSReclaim,   SysMemInfo::kMemSUnreclaim,  SysMemInfo::kMemSwapTotal,
+        SysMemInfo::kMemSwapFree,   SysMemInfo::kMemMapped,      SysMemInfo::kMemVmallocUsed,
+        SysMemInfo::kMemPageTables, SysMemInfo::kMemKernelStack,
 };
 
 bool SysMemInfo::ReadMemInfo(const std::string& path) {
@@ -99,6 +105,7 @@
     buffer[len] = '\0';
     char* p = buffer;
     uint32_t found = 0;
+    uint32_t lineno = 0;
     while (*p && found < tags.size()) {
         for (auto& tag : tags) {
             if (strncmp(p, tag.c_str(), tag.size()) == 0) {
@@ -107,7 +114,7 @@
                 char* endptr = nullptr;
                 mem_in_kb_[tag] = strtoull(p, &endptr, 10);
                 if (p == endptr) {
-                    PLOG(ERROR) << "Failed to parse line in file: " << path;
+                    PLOG(ERROR) << "Failed to parse line:" << lineno + 1 << " in file: " << path;
                     return false;
                 }
                 p = endptr;
@@ -119,11 +126,75 @@
             p++;
         }
         if (*p) p++;
+        lineno++;
     }
 
     return true;
 }
 #endif
 
+uint64_t SysMemInfo::mem_zram_kb(const std::string& zram_dev) {
+    uint64_t mem_zram_total = 0;
+    if (!zram_dev.empty()) {
+        if (!MemZramDevice(zram_dev, &mem_zram_total)) {
+            return 0;
+        }
+        return mem_zram_total / 1024;
+    }
+
+    constexpr uint32_t kMaxZramDevices = 256;
+    for (uint32_t i = 0; i < kMaxZramDevices; i++) {
+        std::string zram_dev = ::android::base::StringPrintf("/sys/block/zram%u/", i);
+        if (access(zram_dev.c_str(), F_OK)) {
+            // We assume zram devices appear in range 0-255 and appear always in sequence
+            // under /sys/block. So, stop looking for them once we find one is missing.
+            break;
+        }
+
+        uint64_t mem_zram_dev;
+        if (!MemZramDevice(zram_dev, &mem_zram_dev)) {
+            return 0;
+        }
+
+        mem_zram_total += mem_zram_dev;
+    }
+
+    return mem_zram_total / 1024;
+}
+
+bool SysMemInfo::MemZramDevice(const std::string& zram_dev, uint64_t* mem_zram_dev) {
+    std::string content;
+    if (android::base::ReadFileToString(zram_dev + "mm_stat", &content)) {
+        std::vector<std::string> values = ::android::base::Split(content, " ");
+        if (values.size() < 3) {
+            LOG(ERROR) << "Malformed mm_stat file for zram dev: " << zram_dev
+                       << " content: " << content;
+            return false;
+        }
+
+        if (!::android::base::ParseUint(values[2], mem_zram_dev)) {
+            LOG(ERROR) << "Malformed mm_stat file for zram dev: " << zram_dev
+                       << " value: " << values[2];
+            return false;
+        }
+
+        return true;
+    }
+
+    if (::android::base::ReadFileToString(zram_dev + "mem_used_total", &content)) {
+        *mem_zram_dev = strtoull(content.c_str(), NULL, 10);
+        if (*mem_zram_dev == ULLONG_MAX) {
+            PLOG(ERROR) << "Malformed mem_used_total file for zram dev: " << zram_dev
+                        << " content: " << content;
+            return false;
+        }
+
+        return true;
+    }
+
+    LOG(ERROR) << "Can't find memory status under: " << zram_dev;
+    return false;
+}
+
 }  // namespace meminfo
 }  // namespace android
diff --git a/libmeminfo/testdata1/mm_stat b/libmeminfo/testdata1/mm_stat
new file mode 100644
index 0000000..684f567
--- /dev/null
+++ b/libmeminfo/testdata1/mm_stat
@@ -0,0 +1 @@
+145674240 26801454 31236096        0 45772800     3042     1887      517
diff --git a/libmeminfo/testdata2/mem_used_total b/libmeminfo/testdata2/mem_used_total
new file mode 100644
index 0000000..97fcf41
--- /dev/null
+++ b/libmeminfo/testdata2/mem_used_total
@@ -0,0 +1 @@
+31236096
diff --git a/libmeminfo/tools/Android.bp b/libmeminfo/tools/Android.bp
index 0870130..7c41660 100644
--- a/libmeminfo/tools/Android.bp
+++ b/libmeminfo/tools/Android.bp
@@ -25,3 +25,18 @@
         "libmeminfo",
     ],
 }
+
+cc_binary {
+    name: "procrank2",
+    cflags: [
+        "-Wall",
+        "-Werror",
+        "-Wno-unused-parameter",
+    ],
+
+    srcs: ["procrank.cpp"],
+    shared_libs: [
+        "libbase",
+        "libmeminfo",
+    ],
+}
diff --git a/libmeminfo/tools/procmem.cpp b/libmeminfo/tools/procmem.cpp
index 3571e41..d30c2f2 100644
--- a/libmeminfo/tools/procmem.cpp
+++ b/libmeminfo/tools/procmem.cpp
@@ -66,14 +66,12 @@
     // clear string stream first.
     ss.str("");
     // TODO: use ::android::base::StringPrintf instead of <iomanip> here.
-    if (!show_wss)
-        ss << std::setw(6) << usage.vss/1024 << padding;
-    ss << std::setw(6) << usage.rss/1024 << padding << std::setw(6)
-       << usage.pss/1024 << padding << std::setw(6) << usage.uss/1024 << padding
-       << std::setw(6) << usage.shared_clean/1024 << padding << std::setw(6)
-       << usage.shared_dirty/1024 << padding << std::setw(6)
-       << usage.private_clean/1024 << padding << std::setw(6)
-       << usage.private_dirty/1024 << padding;
+    if (!show_wss) ss << std::setw(6) << usage.vss / 1024 << padding;
+    ss << std::setw(6) << usage.rss / 1024 << padding << std::setw(6) << usage.pss / 1024 << padding
+       << std::setw(6) << usage.uss / 1024 << padding << std::setw(6) << usage.shared_clean / 1024
+       << padding << std::setw(6) << usage.shared_dirty / 1024 << padding << std::setw(6)
+       << usage.private_clean / 1024 << padding << std::setw(6) << usage.private_dirty / 1024
+       << padding;
 }
 
 static int show(ProcMemInfo& proc, bool hide_zeroes, bool show_wss) {
@@ -158,14 +156,14 @@
     }
 
     bool need_wss = wss_reset || show_wss;
-    ProcMemInfo proc(pid, need_wss);
     if (wss_reset) {
-        if (!proc.WssReset()) {
+        if (!ProcMemInfo::ResetWorkingSet(pid)) {
             std::cerr << "Failed to reset working set of pid : " << pid << std::endl;
             exit(EXIT_FAILURE);
         }
         return 0;
     }
 
+    ProcMemInfo proc(pid, need_wss);
     return show(proc, hide_zeroes, show_wss);
 }
diff --git a/libmeminfo/tools/procrank.cpp b/libmeminfo/tools/procrank.cpp
new file mode 100644
index 0000000..e39e7fa
--- /dev/null
+++ b/libmeminfo/tools/procrank.cpp
@@ -0,0 +1,530 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <dirent.h>
+#include <errno.h>
+#include <inttypes.h>
+#include <linux/kernel-page-flags.h>
+#include <linux/oom.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <iostream>
+#include <memory>
+#include <sstream>
+#include <vector>
+
+#include <android-base/file.h>
+#include <android-base/parseint.h>
+#include <android-base/stringprintf.h>
+#include <android-base/strings.h>
+
+#include <meminfo/procmeminfo.h>
+#include <meminfo/sysmeminfo.h>
+
+using ::android::meminfo::MemUsage;
+using ::android::meminfo::ProcMemInfo;
+
+struct ProcessRecord {
+  public:
+    ProcessRecord(pid_t pid, bool get_wss = false, uint64_t pgflags = 0, uint64_t pgflags_mask = 0)
+        : pid_(-1),
+          procmem_(nullptr),
+          oomadj_(OOM_SCORE_ADJ_MAX + 1),
+          cmdline_(""),
+          proportional_swap_(0),
+          unique_swap_(0),
+          zswap_(0) {
+        std::unique_ptr<ProcMemInfo> procmem =
+                std::make_unique<ProcMemInfo>(pid, get_wss, pgflags, pgflags_mask);
+        if (procmem == nullptr) {
+            std::cerr << "Failed to create ProcMemInfo for: " << pid << std::endl;
+            return;
+        }
+
+        std::string fname = ::android::base::StringPrintf("/proc/%d/oom_score_adj", pid);
+        auto oomscore_fp =
+                std::unique_ptr<FILE, decltype(&fclose)>{fopen(fname.c_str(), "re"), fclose};
+        if (oomscore_fp == nullptr) {
+            std::cerr << "Failed to open oom_score_adj file: " << fname << std::endl;
+            return;
+        }
+
+        if (fscanf(oomscore_fp.get(), "%d\n", &oomadj_) != 1) {
+            std::cerr << "Failed to read oomadj from: " << fname << std::endl;
+            return;
+        }
+
+        fname = ::android::base::StringPrintf("/proc/%d/cmdline", pid);
+        if (!::android::base::ReadFileToString(fname, &cmdline_)) {
+            std::cerr << "Failed to read cmdline from: " << fname << std::endl;
+            cmdline_ = "<unknown>";
+        }
+        // We deliberately don't read the proc/<pid>cmdline file directly into 'cmdline_'
+        // because of some processes showing up cmdlines that end with "0x00 0x0A 0x00"
+        // e.g. xtra-daemon, lowi-server
+        // The .c_str() assignment below then takes care of trimming the cmdline at the first
+        // 0x00. This is how original procrank worked (luckily)
+        cmdline_.resize(strlen(cmdline_.c_str()));
+        procmem_ = std::move(procmem);
+        pid_ = pid;
+    }
+
+    bool valid() const { return pid_ != -1; }
+
+    void CalculateSwap(const uint16_t* swap_offset_array, float zram_compression_ratio) {
+        const std::vector<uint16_t>& swp_offs = procmem_->SwapOffsets();
+        for (auto& off : swp_offs) {
+            proportional_swap_ += getpagesize() / swap_offset_array[off];
+            unique_swap_ += swap_offset_array[off] == 1 ? getpagesize() : 0;
+            zswap_ = proportional_swap_ * zram_compression_ratio;
+        }
+    }
+
+    // Getters
+    pid_t pid() const { return pid_; }
+    const std::string& cmdline() const { return cmdline_; }
+    int32_t oomadj() const { return oomadj_; }
+    uint64_t proportional_swap() const { return proportional_swap_; }
+    uint64_t unique_swap() const { return unique_swap_; }
+    uint64_t zswap() const { return zswap_; }
+
+    // Wrappers to ProcMemInfo
+    const std::vector<uint16_t>& SwapOffsets() const { return procmem_->SwapOffsets(); }
+    const MemUsage& Usage() const { return procmem_->Usage(); }
+    const MemUsage& Wss() const { return procmem_->Wss(); }
+
+  private:
+    pid_t pid_;
+    std::unique_ptr<ProcMemInfo> procmem_;
+    int32_t oomadj_;
+    std::string cmdline_;
+    uint64_t proportional_swap_;
+    uint64_t unique_swap_;
+    uint64_t zswap_;
+};
+
+// Show working set instead of memory consumption
+bool show_wss = false;
+// Reset working set of each process
+bool reset_wss = false;
+// Show per-process oom_score_adj column
+bool show_oomadj = false;
+// True if the device has swap enabled
+bool has_swap = false;
+// True, if device has zram enabled
+bool has_zram = false;
+// If zram is enabled, the compression ratio is zram used / swap used.
+float zram_compression_ratio = 0.0;
+// Sort process in reverse, default is descending
+bool reverse_sort = false;
+
+// Calculated total memory usage across all processes in the system
+uint64_t total_pss = 0;
+uint64_t total_uss = 0;
+uint64_t total_swap = 0;
+uint64_t total_pswap = 0;
+uint64_t total_uswap = 0;
+uint64_t total_zswap = 0;
+
+static void usage(const char* myname) {
+    std::cerr << "Usage: " << myname << " [ -W ] [ -v | -r | -p | -u | -s | -h ]" << std::endl
+              << "    -v  Sort by VSS." << std::endl
+              << "    -r  Sort by RSS." << std::endl
+              << "    -p  Sort by PSS." << std::endl
+              << "    -u  Sort by USS." << std::endl
+              << "    -s  Sort by swap." << std::endl
+              << "        (Default sort order is PSS.)" << std::endl
+              << "    -R  Reverse sort order (default is descending)." << std::endl
+              << "    -c  Only show cached (storage backed) pages" << std::endl
+              << "    -C  Only show non-cached (ram/swap backed) pages" << std::endl
+              << "    -k  Only show pages collapsed by KSM" << std::endl
+              << "    -w  Display statistics for working set only." << std::endl
+              << "    -W  Reset working set of all processes." << std::endl
+              << "    -o  Show and sort by oom score against lowmemorykiller thresholds."
+              << std::endl
+              << "    -h  Display this help screen." << std::endl;
+}
+
+static bool read_all_pids(std::vector<pid_t>* pids, std::function<bool(pid_t pid)> for_each_pid) {
+    pids->clear();
+    std::unique_ptr<DIR, int (*)(DIR*)> procdir(opendir("/proc"), closedir);
+    if (!procdir) return false;
+
+    struct dirent* dir;
+    pid_t pid;
+    while ((dir = readdir(procdir.get()))) {
+        if (!::android::base::ParseInt(dir->d_name, &pid)) continue;
+        if (!for_each_pid(pid)) return false;
+        pids->push_back(pid);
+    }
+
+    return true;
+}
+
+static bool count_swap_offsets(const ProcessRecord& proc, uint16_t* swap_offset_array,
+                               uint32_t size) {
+    const std::vector<uint16_t>& swp_offs = proc.SwapOffsets();
+    for (auto& off : swp_offs) {
+        if (off >= size) {
+            std::cerr << "swap offset " << off << " is out of bounds for process: " << proc.pid()
+                      << std::endl;
+            return false;
+        }
+
+        if (swap_offset_array[off] == USHRT_MAX) {
+            std::cerr << "swap offset " << off << " ref count overflow in process: " << proc.pid()
+                      << std::endl;
+            return false;
+        }
+
+        swap_offset_array[off]++;
+    }
+
+    return true;
+}
+
+static void print_header(std::stringstream& ss) {
+    ss.str("");
+    ss << ::android::base::StringPrintf("%5s  ", "PID");
+    if (show_oomadj) {
+        ss << ::android::base::StringPrintf("%5s  ", "oom");
+    }
+
+    if (show_wss) {
+        ss << ::android::base::StringPrintf("%7s  %7s  %7s  ", "WRss", "WPss", "WUss");
+        // now swap statistics here, working set pages by definition shouldn't end up in swap.
+    } else {
+        ss << ::android::base::StringPrintf("%8s  %7s  %7s  %7s  ", "Vss", "Rss", "Pss", "Uss");
+        if (has_swap) {
+            ss << ::android::base::StringPrintf("%7s  %7s  %7s  ", "Swap", "PSwap", "USwap");
+            if (has_zram) {
+                ss << ::android::base::StringPrintf("%7s  ", "ZSwap");
+            }
+        }
+    }
+
+    ss << "cmdline";
+}
+
+static void print_process_record(std::stringstream& ss, ProcessRecord& proc) {
+    ss << ::android::base::StringPrintf("%5d  ", proc.pid());
+    if (show_oomadj) {
+        ss << ::android::base::StringPrintf("%5d  ", proc.oomadj());
+    }
+
+    if (show_wss) {
+        ss << ::android::base::StringPrintf("%6" PRIu64 "K  %6" PRIu64 "K  %6" PRIu64 "K  ",
+                                            proc.Wss().rss / 1024, proc.Wss().pss / 1024,
+                                            proc.Wss().uss / 1024);
+    } else {
+        ss << ::android::base::StringPrintf("%7" PRIu64 "K  %6" PRIu64 "K  %6" PRIu64 "K  %6" PRIu64
+                                            "K  ",
+                                            proc.Usage().vss / 1024, proc.Usage().rss / 1024,
+                                            proc.Usage().pss / 1024, proc.Usage().uss / 1024);
+        if (has_swap) {
+            ss << ::android::base::StringPrintf("%6" PRIu64 "K  ", proc.Usage().swap / 1024);
+            ss << ::android::base::StringPrintf("%6" PRIu64 "K  ", proc.proportional_swap() / 1024);
+            ss << ::android::base::StringPrintf("%6" PRIu64 "K  ", proc.unique_swap() / 1024);
+            if (has_zram) {
+                ss << ::android::base::StringPrintf("%6" PRIu64 "K  ", (proc.zswap() / 1024));
+            }
+        }
+    }
+}
+
+static void print_processes(std::stringstream& ss, std::vector<ProcessRecord>& procs,
+                            uint16_t* swap_offset_array) {
+    for (auto& proc : procs) {
+        total_pss += show_wss ? proc.Wss().pss : proc.Usage().pss;
+        total_uss += show_wss ? proc.Wss().uss : proc.Usage().uss;
+        if (!show_wss && has_swap) {
+            proc.CalculateSwap(swap_offset_array, zram_compression_ratio);
+            total_swap += proc.Usage().swap;
+            total_pswap += proc.proportional_swap();
+            total_uswap += proc.unique_swap();
+            if (has_zram) {
+                total_zswap += proc.zswap();
+            }
+        }
+
+        print_process_record(ss, proc);
+        ss << proc.cmdline() << std::endl;
+    }
+}
+
+static void print_separator(std::stringstream& ss) {
+    ss << ::android::base::StringPrintf("%5s  ", "");
+    if (show_oomadj) {
+        ss << ::android::base::StringPrintf("%5s  ", "");
+    }
+
+    if (show_wss) {
+        ss << ::android::base::StringPrintf("%7s  %7s  %7s  ", "", "------", "------");
+    } else {
+        ss << ::android::base::StringPrintf("%8s  %7s  %7s  %7s  ", "", "", "------", "------");
+        if (has_swap) {
+            ss << ::android::base::StringPrintf("%7s  %7s  %7s  ", "------", "------", "------");
+            if (has_zram) {
+                ss << ::android::base::StringPrintf("%7s  ", "------");
+            }
+        }
+    }
+
+    ss << ::android::base::StringPrintf("%s", "------");
+}
+
+static void print_totals(std::stringstream& ss) {
+    ss << ::android::base::StringPrintf("%5s  ", "");
+    if (show_oomadj) {
+        ss << ::android::base::StringPrintf("%5s  ", "");
+    }
+
+    if (show_wss) {
+        ss << ::android::base::StringPrintf("%7s  %6" PRIu64 "K  %6" PRIu64 "K  ", "",
+                                            total_pss / 1024, total_uss / 1024);
+    } else {
+        ss << ::android::base::StringPrintf("%8s  %7s  %6" PRIu64 "K  %6" PRIu64 "K  ", "", "",
+                                            total_pss / 1024, total_uss / 1024);
+        if (has_swap) {
+            ss << ::android::base::StringPrintf("%6" PRIu64 "K  ", total_swap / 1024);
+            ss << ::android::base::StringPrintf("%6" PRIu64 "K  ", total_pswap / 1024);
+            ss << ::android::base::StringPrintf("%6" PRIu64 "K  ", total_uswap / 1024);
+            if (has_zram) {
+                ss << ::android::base::StringPrintf("%6" PRIu64 "K  ", total_zswap / 1024);
+            }
+        }
+    }
+    ss << "TOTAL";
+}
+
+static void print_sysmeminfo(std::stringstream& ss, ::android::meminfo::SysMemInfo& smi) {
+    if (has_swap) {
+        ss << ::android::base::StringPrintf("ZRAM: %" PRIu64 "K physical used for %" PRIu64
+                                            "K in swap "
+                                            "(%" PRIu64 "K total swap)",
+                                            smi.mem_zram_kb(),
+                                            (smi.mem_swap_kb() - smi.mem_swap_free_kb()),
+                                            smi.mem_swap_kb())
+           << std::endl;
+    }
+
+    ss << ::android::base::StringPrintf(" RAM: %" PRIu64 "K total, %" PRIu64 "K free, %" PRIu64
+                                        "K buffers, "
+                                        "%" PRIu64 "K cached, %" PRIu64 "K shmem, %" PRIu64
+                                        "K slab",
+                                        smi.mem_total_kb(), smi.mem_free_kb(), smi.mem_buffers_kb(),
+                                        smi.mem_cached_kb(), smi.mem_shmem_kb(), smi.mem_slab_kb());
+}
+
+int main(int argc, char* argv[]) {
+    auto pss_sort = [](ProcessRecord& a, ProcessRecord& b) {
+        MemUsage stats_a = show_wss ? a.Wss() : a.Usage();
+        MemUsage stats_b = show_wss ? b.Wss() : b.Usage();
+        return reverse_sort ? stats_a.pss < stats_b.pss : stats_a.pss > stats_b.pss;
+    };
+
+    auto uss_sort = [](ProcessRecord& a, ProcessRecord& b) {
+        MemUsage stats_a = show_wss ? a.Wss() : a.Usage();
+        MemUsage stats_b = show_wss ? b.Wss() : b.Usage();
+        return reverse_sort ? stats_a.uss < stats_b.uss : stats_a.uss > stats_b.uss;
+    };
+
+    auto rss_sort = [](ProcessRecord& a, ProcessRecord& b) {
+        MemUsage stats_a = show_wss ? a.Wss() : a.Usage();
+        MemUsage stats_b = show_wss ? b.Wss() : b.Usage();
+        return reverse_sort ? stats_a.rss < stats_b.pss : stats_a.pss > stats_b.pss;
+    };
+
+    auto vss_sort = [](ProcessRecord& a, ProcessRecord& b) {
+        MemUsage stats_a = show_wss ? a.Wss() : a.Usage();
+        MemUsage stats_b = show_wss ? b.Wss() : b.Usage();
+        return reverse_sort ? stats_a.vss < stats_b.vss : stats_a.vss > stats_b.vss;
+    };
+
+    auto swap_sort = [](ProcessRecord& a, ProcessRecord& b) {
+        MemUsage stats_a = show_wss ? a.Wss() : a.Usage();
+        MemUsage stats_b = show_wss ? b.Wss() : b.Usage();
+        return reverse_sort ? stats_a.swap < stats_b.swap : stats_a.swap > stats_b.swap;
+    };
+
+    auto oomadj_sort = [](ProcessRecord& a, ProcessRecord& b) {
+        return reverse_sort ? a.oomadj() < b.oomadj() : a.oomadj() > b.oomadj();
+    };
+
+    // default PSS sort
+    std::function<bool(ProcessRecord & a, ProcessRecord & b)> proc_sort = pss_sort;
+
+    // count all pages by default
+    uint64_t pgflags = 0;
+    uint64_t pgflags_mask = 0;
+
+    int opt;
+    while ((opt = getopt(argc, argv, "cChkoprRsuvwW")) != -1) {
+        switch (opt) {
+            case 'c':
+                pgflags = 0;
+                pgflags_mask = (1 << KPF_SWAPBACKED);
+                break;
+            case 'C':
+                pgflags = (1 << KPF_SWAPBACKED);
+                pgflags_mask = (1 << KPF_SWAPBACKED);
+                break;
+            case 'h':
+                usage(argv[0]);
+                return 0;
+                break;
+            case 'k':
+                pgflags = (1 << KPF_KSM);
+                pgflags_mask = (1 << KPF_KSM);
+                break;
+            case 'o':
+                proc_sort = oomadj_sort;
+                show_oomadj = true;
+                break;
+            case 'p':
+                proc_sort = pss_sort;
+                break;
+            case 'r':
+                proc_sort = rss_sort;
+                break;
+            case 'R':
+                reverse_sort = true;
+                break;
+            case 's':
+                proc_sort = swap_sort;
+                break;
+            case 'u':
+                proc_sort = uss_sort;
+                break;
+            case 'v':
+                proc_sort = vss_sort;
+                break;
+            case 'w':
+                show_wss = true;
+                break;
+            case 'W':
+                reset_wss = true;
+                break;
+            default:
+                abort();
+        }
+    }
+
+    std::vector<pid_t> pids;
+    std::vector<ProcessRecord> procs;
+    if (reset_wss) {
+        if (!read_all_pids(&pids,
+                           [&](pid_t pid) -> bool { return ProcMemInfo::ResetWorkingSet(pid); })) {
+            std::cerr << "Failed to reset working set of all processes" << std::endl;
+            exit(EXIT_FAILURE);
+        }
+        // we are done, all other options passed to procrank are ignored in the presence of '-W'
+        return 0;
+    }
+
+    ::android::meminfo::SysMemInfo smi;
+    if (!smi.ReadMemInfo()) {
+        std::cerr << "Failed to get system memory info" << std::endl;
+        exit(EXIT_FAILURE);
+    }
+
+    // Figure out swap and zram
+    uint64_t swap_total = smi.mem_swap_kb() * 1024;
+    has_swap = swap_total > 0;
+    // Allocate the swap array
+    auto swap_offset_array = std::make_unique<uint16_t[]>(swap_total / getpagesize());
+    if (has_swap) {
+        has_zram = smi.mem_zram_kb() > 0;
+        if (has_zram) {
+            zram_compression_ratio = static_cast<float>(smi.mem_zram_kb()) /
+                                     (smi.mem_swap_kb() - smi.mem_swap_free_kb());
+        }
+    }
+
+    auto mark_swap_usage = [&](pid_t pid) -> bool {
+        ProcessRecord proc(pid, show_wss, pgflags, pgflags_mask);
+        if (!proc.valid()) {
+            std::cerr << "Failed to create process record for: " << pid << std::endl;
+            return false;
+        }
+
+        // Skip processes with no memory mappings
+        uint64_t vss = show_wss ? proc.Wss().vss : proc.Usage().vss;
+        if (vss == 0) return true;
+
+        // collect swap_offset counts from all processes in 1st pass
+        if (!show_wss && has_swap &&
+            !count_swap_offsets(proc, swap_offset_array.get(), swap_total / getpagesize())) {
+            std::cerr << "Failed to count swap offsets for process: " << pid << std::endl;
+            return false;
+        }
+
+        procs.push_back(std::move(proc));
+        return true;
+    };
+
+    // Get a list of all pids currently running in the system in
+    // 1st pass through all processes. Mark each swap offset used by the process as we find them
+    // for calculating proportional swap usage later.
+    if (!read_all_pids(&pids, mark_swap_usage)) {
+        std::cerr << "Failed to read all pids from the system" << std::endl;
+        exit(EXIT_FAILURE);
+    }
+
+    std::stringstream ss;
+    if (procs.empty()) {
+        // This would happen in corner cases where procrank is being run to find KSM usage on a
+        // system with no KSM and combined with working set determination as follows
+        //   procrank -w -u -k
+        //   procrank -w -s -k
+        //   procrank -w -o -k
+        ss << "<empty>" << std::endl << std::endl;
+        print_sysmeminfo(ss, smi);
+        ss << std::endl;
+        std::cout << ss.str();
+        return 0;
+    }
+
+    // Sort all process records, default is PSS descending
+    std::sort(procs.begin(), procs.end(), proc_sort);
+
+    // start dumping output in string stream
+    print_header(ss);
+    ss << std::endl;
+
+    // 2nd pass to calculate and get per process stats to add them up
+    print_processes(ss, procs, swap_offset_array.get());
+
+    // Add separator to output
+    print_separator(ss);
+    ss << std::endl;
+
+    // Add totals to output
+    print_totals(ss);
+    ss << std::endl << std::endl;
+
+    // Add system information at the end
+    print_sysmeminfo(ss, smi);
+    ss << std::endl;
+
+    // dump on the screen
+    std::cout << ss.str();
+
+    return 0;
+}