Memory usage reporting for FreeBSD is incorrect

[Low-power]

Firstly the biggest issue, htop didn't count the 'inactive' memory (vm.stats.vm.v_inactive_count) as used memory, but as free; this is incorrect. The inactive pages reported by the kernel are memory pages allocated by user space programs that are not recently used, and are therefore available for swapping out in case system is short in memory; these are definitely not free pages. This part of memory is usually considerably big in most systems, as a result htop had wrongly reported a big part of memory as 'free'.

Additionally the VFS buffer size as reported in vfs.bufspace (which belongs to caches in htop's view) is actually included in the 'wired' memory (vm.stats.vm.v_wire_count). The total used memory in htop should be subtracted by this size.

htop also mistakenly mapped kFreeBSD 'VFS buffer' into its own 'buffers' memory class, but this Linux-originated 'buffers' memory don't have the same meaning. VFS buffer is actually used for file system caches, utilized by most file systems other than ZFS.

Along with the bug fixes, the corresponding comments has also been corrected and extended to better document the memory class mapping between htop and kFreeBSD.

[BenBE]

LGTM.

Are the values memWire, memActive, and memInactive from the FreeBSDMaschine structure used anywhere outside FreeBSDMaschine_scanMemoryInformation?

[Low-power]

Are the values memWire, memActive, and memInactive from the FreeBSDMaschine structure used anywhere outside FreeBSDMaschine_scanMemoryInformation?

I don't think they are. They can be turned into on-stack variables, but I'm lazy to touch them at this moment...

[BenBE]

Could you prepend the following patch to your PR?

diff --git a/freebsd/FreeBSDMachine.c b/freebsd/FreeBSDMachine.c
index d781414b..3a478679 100644
--- a/freebsd/FreeBSDMachine.c
+++ b/freebsd/FreeBSDMachine.c
@@ -340,12 +340,10 @@ static void FreeBSDMachine_scanMemoryInfo(Machine* super) {
    len = sizeof(memActive);
    sysctl(MIB_vm_stats_vm_v_active_count, 4, &(memActive), &len, NULL, 0);
    memActive *= this->pageSizeKb;
-   this->memActive = memActive;
 
    len = sizeof(memWire);
    sysctl(MIB_vm_stats_vm_v_wire_count, 4, &(memWire), &len, NULL, 0);
    memWire *= this->pageSizeKb;
-   this->memWire = memWire;
 
    len = sizeof(buffersMem);
    sysctl(MIB_vfs_bufspace, 2, &(buffersMem), &len, NULL, 0);
@@ -361,7 +359,7 @@ static void FreeBSDMachine_scanMemoryInfo(Machine* super) {
    sysctl(MIB_vm_vmtotal, 2, &(vmtotal), &len, NULL, 0);
    super->sharedMem = vmtotal.t_rmshr * this->pageSizeKb;
 
-   super->usedMem = this->memActive + this->memWire;
+   super->usedMem = memActive + memWire;
 
    struct kvm_swap swap[16];
    int nswap = kvm_getswapinfo(this->kd, swap, ARRAYSIZE(swap), 0);
diff --git a/freebsd/FreeBSDMachine.h b/freebsd/FreeBSDMachine.h
index f34b568e..0f9c33f2 100644
--- a/freebsd/FreeBSDMachine.h
+++ b/freebsd/FreeBSDMachine.h
@@ -36,9 +36,6 @@ typedef struct FreeBSDMachine_ {
    int pageSizeKb;
    int kernelFScale;
 
-   unsigned long long int memWire;
-   unsigned long long int memActive;
-
    ZfsArcStats zfs;
 
    CPUData* cpus;

TIA.

[Low-power]

Rebased.