[BUG] macOS Match Activity Monitor with Memory Usage Stats

[samuelvenable]

Read the FAQ first

• I have checked the FAQ but the issue is not covered

Description

I have tried getting memory usage with fastfetch but it is not matching up with Activity Monitor. If you don't feel like compiling anything, here's a quick shell script which gets ram usage much closer to how Activity Monitor does it, (if not exactly how it does it, it's very close): https://gist.github.com/samuelvenable/550bb8922a4bc137aa9b240fa694c020

#!/bin/sh
# macOS Memory Usage Statistics Shell Script
# Show Physical Memory and Memory Used Stats
# This Matches Up with Activity Monitor App!
# View vm_stat Source Code for More Details:
# https://github.com/st3fan/osx-10.9/blob/34e34a6a539b5a822cda4074e56a7ced9b57da71/system_cmds-597.1.1/vm_stat.tproj/vm_stat.c#L135-L160
free_count=$(vm_stat | grep "Pages free:" | awk '{gsub(/\./, "");print $3}')
external_page_count=$(vm_stat | grep "File-backed pages:" | awk '{gsub(/\./, "");print $3}')
page_size=$(vm_stat | grep "page size of" | awk '{print $8}')
free_page_count=$((free_count + external_page_count))
physical_memory=$(sysctl -n hw.memsize)
free_memory=$((free_page_count * page_size))
used_memory=$((physical_memory - free_memory))
gb_physical_memory=$(awk -v physical_memory="$physical_memory" 'BEGIN{result=physical_memory / 1024 / 1024 / 1024;print result}')
gb_free_memory=$(awk -F'.' -v used_memory="$used_memory" 'BEGIN{result=used_memory / 1024 / 1024 / 1024;print result}')
gb_used_memory=$(awk -F'.' -v free_memory="$free_memory" 'BEGIN{result=free_memory / 1024 / 1024 / 1024;print result}')
truncated_gb_physical_memory=$(awk -F'.' -v gb_physical_memory="$gb_physical_memory" 'BEGIN{printf "%.2f",gb_physical_memory}')
truncated_gb_free_memory=$(awk -F'.' -v gb_used_memory="$gb_used_memory" 'BEGIN{printf "%.2f",gb_used_memory}')
truncated_gb_used_memory=$(awk -F'.' -v gb_free_memory="$gb_free_memory" 'BEGIN{printf "%.2f",gb_free_memory}')
echo Physical Memory: $truncated_gb_physical_memory GB
echo Memory Used: $truncated_gb_used_memory GB
echo Memory Free: $truncated_gb_free_memory GB

C equivalent:

#include "memory.h"

#include <string.h>
#include <mach/mach.h>
#include <sys/sysctl.h>
#include <unistd.h>

const char* ffDetectMemory(FFMemoryResult* ram)
{
    size_t length = sizeof(ram->bytesTotal);
    if (sysctl((int[]){ CTL_HW, HW_MEMSIZE }, 2, &ram->bytesTotal, &length, NULL, 0) != 0)
        return "Failed to read hw.memsize";

    mach_msg_type_number_t count = HOST_VM_INFO64_COUNT;
    vm_statistics64_data_t vmstat;
    if(host_statistics64(mach_host_self(), HOST_VM_INFO64, (host_info64_t) (&vmstat), &count) != KERN_SUCCESS)
        return "Failed to read host_statistics64";

    // Match what Activity Monitor does: https://github.com/st3fan/osx-10.9/blob/34e34a6a539b5a822cda4074e56a7ced9b57da71/system_cmds-597.1.1/vm_stat.tproj/vm_stat.c#L139
    ram->bytesUsed = ram->bytesTotal - ((uint64_t)(vmstat.free_count - vmstat.speculative_count) + vmstat.external_page_count) * instance.state.platform.sysinfo.pageSize;

    return NULL;
}

I'm not sure why but when I test the above code in my own C program it matches Activity Monitor perfectly. But when I use it in fastfetch the values are slightly off by a bit; this is likely due to how fastfetch handles rounding up/down.

Version used

fastfetch 2.58.0-4 (aarch64)

Bug prevalence

Always

Regression

No

Installation

Built from source

Package manager

No response

Screenshots

No response

Configuration

No response

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Features built-in

threads
vulkan
zlib
sqlite3
libzfs

[CarterLi]

View vm_stat Source Code for More Details

vm_stat is NOT Activity Monitor; they are different binaries, and different programs use different algorithms. The most obvious one is /usr/bin/top, which reports a much higher memory usage.

I have tried getting memory usage with fastfetch but it is not matching up with Activity Monitor

This is what I got on my MBP for the current implementation. At least it matches Activity Monitor for me very well

output.mp4

I'm OK to accept improvements. Before that, you need to clarify why I'm wrong / what part is wrong and why yours is better. Remember that Activity Monitor is closed source, unless you can decompile it, there is no 3rd-party implementation that is ABSOLUTELY right or wrong.

Thanks.

[samuelvenable]

I was not claiming vm_stat and Activity Monitor to be the same binary. However, they do more than likely use very similar algorithms under-the-hood to calculate used memory. I linked to vm_stat's source code for reference and as an attempt to explain that. ram->bytesUsed = ram->bytesTotal - ((uint64_t)(vmstat.free_count - vmstat.speculative_count) + vmstat.external_page_count) * instance.state.platform.sysinfo.pageSize gives the same results Activity Monitor does for Memory Used. You can see this from your own testing. What makes my solution better is it accomplishes your same initial goal but with less lines code and less code logic applied. vm_stat uses vmstat.free_count - vmstat.speculative_count to calculate free pages, as can be seen in the source code. Add vmstat.external_page_count to it, then multiply by page size, and subtract the result from total Physical Memory, and then it matches Activity Monitor. What else do you want me to say? Again, you can try the shell script I provided in the ticket OP, or if you want to test the C equivalent within fastfetch itself, try:

git clone https://github.com/samuelvenable/fastfetch ~/fastfetch
cd ~/fastfetch && cmake . && make && ./fastfetch -s memory -l none --dynamic-interval 1000 --no-buffer

My memory was wrong that your code didn't give the right values. However, my solution is still less lines of code overall. 👍

[CarterLi]

Not sure why you insist that your code less lines code and less code logic applied. If you want less lines, you may collapse them into:

ram->bytesUsed = (ram->bytesTotal - usableMemory) + (uint64_t)(vmstat.internal_page_count + vmstat.wire_count + vmstat.compressor_page_count) * instance.state.platform.sysinfo.pageSize;

The only downside is that host_statistics64 doesn't report usableMemory/reservedMemory, so I have to acquire it by another sysctl call.

The reason I prefer spliting them into multiple lines, is that I want to replicate what Activity Monitor does. Activity Monitor clearly reports that Memory Used is calcuated with

1. App Memory
2. Wired Memory
3. Compressed

Calcuating them separately can better represent the algorithm that I use. I like self-documenting code.

Note: On systems other than macOS where reserved memory is not included in total memory (that's why you see the total memory size is slightly smaller than the physically installed memroy size on most systems), used memory equals App Memory + Wired Memory + Compressed. I actually considered reporting App Memory + Wired Memory + Compressed directly as Memory Used and hw.memsize_usable as Total Memory for consistency with Linux, Windows and BSDs, but I still decided not to do that because I know it's controversial.

[samuelvenable]

If Memory Used really is a direct combination of App Memory + Wired Memory + Compressed, then I wonder why your code for App Memory doesn't align with Activity Monitor; everything else matches perfectly except App Memory. Compressed Memory always reports zero for me in Activity Monitor as well as for the value of vmstat.compressor_page_count. I noticed in the video you provided, Compressed Memory is greater than zero for you. I was wondering if you could test my fastfetch fork and compare it with Activity Monitor on your end, for my own educational value I'd like to know whether my code still matches it, with Compressed Memory not being taken into account. My guess is if Compressed Memory is greater than zero it would break my code, and they would no longer match. Only way to know for certain is by being able to test that. If you don't wish to test this for me, I understand. This is mainly out of my own curiosity. You are right in that it my code isn't a huge difference in lines.

[CarterLi]

Your code on other systems:

    if((token = strstr(buf, "MemFree:")) != NULL)
        memFree = strtoul(token + strlen("MemFree:"), NULL, 10);

    ram->bytesTotal = memTotal * 1024lu;
    ram->bytesUsed = (memTotal - memFree) * 1024lu;

https://github.com/samuelvenable/fastfetch/blob/dev/src/detection/memory/memory_linux.c#L23-L24

The free memory size reported by kernel, including macOS (a.k.a. darwin), is the memory size that is physically unused. All modern kernels use free memory for buffering and caching to improve performance. When physically free memory is not enough, memory used for buffering and caching can be recycled immediately.

You used MemFree as free memory size. Not saying it was wrong because it's completely about how you define the concept of free memory. However you used ram->bytesTotal - ((uint64_t)(vmstat.free_count - vmstat.speculative_count) + vmstat.external_page_count) * instance.state.platform.sysinfo.pageSize instead of vmstat.free_count * instance.state.platform.sysinfo.pageSize on macOS which is somewhat estimated available memory. They don't match each other. Putting these two methods in one project is wrong.

[samuelvenable]

Your most recent comment didn't address what I was talking about at all.

[CarterLi]

Your most recent comment didn't address what I was talking about at all.

You neither

[samuelvenable]

I kinda did stay on topic though. You abruptly changed the subject to something completely unrelated to this entire thread.

Edit:

Thank you for accepting my changes.