fix(ext/node): fix os.freemem

[kt3k]

This PR updates os.freemem().

• On linux, it uses MemAvailable: of /proc/meminfo.
  • ref: https://github.com/libuv/libuv/blob/a5c01d4de3695e9d9da34cfd643b5ff0ba582ea7/src/unix/linux.c#L2064
• On Windows and Mac, it uses free memory (equivalent of Deno.systemMemoryInfo().free).
  • ref: https://github.com/libuv/libuv/blob/a5c01d4de3695e9d9da34cfd643b5ff0ba582ea7/src/win/util.c#L279
  • ref: https://github.com/libuv/libuv/blob/a5c01d4de3695e9d9da34cfd643b5ff0ba582ea7/src/unix/darwin.c#L104

See #21148 (comment) for details.

closes #21148

[bartlomieju]

There's a test failure to existing test because of this change :(

[kt3k]

Oh, mem_info.available looks 0 (not implemented) on windows and linux..

deno/runtime/ops/os/sys_info.rs

Line 191 in 4ed9278

pub fn mem_info() -> Option<MemInfo> {

[kt3k]

It looks like there's no reliable way to calculate MemAvailable equivalent from what we already have. I now think we need to add special op for this, and it calls /proc/meminfo in linux.

@littledivy @mmastrac Do you happen to know a good way to calculate/simulate MemAvailable value only using libc?

[littledivy]

@kt3k We could implement Deno.systemMemoryInfo().available for Linux systems:

  #[cfg(target_os = "linux")]
  {
    let mut info = std::mem::MaybeUninit::uninit();
    // SAFETY: `info` is a valid pointer to a `libc::sysinfo` struct.
    let res = unsafe { libc::sysinfo(info.as_mut_ptr()) };
    if res == 0 {
      // SAFETY: `sysinfo` initializes the struct.
      let info = unsafe { info.assume_init() };
      let mem_unit = info.mem_unit as u64;
      mem_info.swap_total = info.totalswap * mem_unit;
      mem_info.swap_free = info.freeswap * mem_unit;
      mem_info.total = info.totalram * mem_unit;
      mem_info.free = info.freeram * mem_unit;
      mem_info.buffers = info.bufferram * mem_unit;
    }

    let meminfo = std::fs::read_to_string("/proc/meminfo");
    let line = meminfo.lines().find(|l| l.starts_with("MemAvailable:"));
    if let Some(line) = line {
      let mem = line.split_whitespace().nth(1);
      let mem = mem.and_then(|v| v.parse::<i32>().ok());
      mem_info.available = mem.unwrap_or(0);
    }
}

[kt3k]

@littledivy

We could implement Deno.systemMemoryInfo().available for Linux systems:

Makes sense. Updated

[kt3k]

Assigned free to available as a fallback for the case when MemAvailable: is unavailable in /proc/meminfo. This is the same as what libuv (uv_get_free_memory) does on linux https://github.com/libuv/libuv/blob/a5c01d4de3695e9d9da34cfd643b5ff0ba582ea7/src/unix/linux.c#L2064

[littledivy]

LGTM. Can you also update runtime/ops/os/README.md? -

 `mem_info`

 | Target family | Syscall                                                                                                                                       
 | Description |
 | ------------- | ------------------------------------------------------------------------ 
 --------------------------------------------------------------------- | ----------- |
-| Linux         | sysinfo                                                                                                                                       
+| Linux         | sysinfo and `/proc/meminfo`                                                                                                                        
 | -           |
 | Windows       | `sysinfoapi::GlobalMemoryStatusEx`                                                                                                            
 | -           |
 | macOS         | <br> <pre> sysctl([CTL_HW, HW_MEMSIZE]); <br> sysctl([CTL_VM, 
 VM_SWAPUSAGE]); <br> host_statistics64(mach_host_self(), HOST_VM_INFO64) 
 </pre> | -           |

[kt3k]

Sure!

[roj1512]

Thank you, @kt3k!