How is MemAvailable calculated in Linux? Python version of the kernel calculating the memory stats

memstat.py

pgsize = 4  # kb
total_lowwmark = 0
total_reserved = 0
with open('/proc/zoneinfo') as zoneinfo:
    for line in zoneinfo:
        if 'pages free' in line:
            next(zoneinfo)
            low = int(next(zoneinfo).split()[1])
            high = int(next(zoneinfo).split()[1])
            total_lowwmark += low
        if 'managed' in line:
            managed = int(line.split()[1])
        if 'protection:' in line:
            lowmem = line.strip('protection: ()\n').split(',')
            maxlowmem = max(int(i) for i in lowmem)
            reserved = min(managed, maxlowmem + high)
            total_reserved += reserved

mmstat = {}
with open('/proc/meminfo') as meminfo:
    for line in meminfo:
        field = line.split()
        mmstat[field[0].rstrip(':')] = int(field[1])

free = mmstat['MemFree'] // pgsize
filecache = (mmstat['Active(file)'] + mmstat['Inactive(file)']) // pgsize
sreclaim = mmstat.get('KReclaimable', mmstat['SReclaimable']) // pgsize
available = free - total_reserved + (filecache - min(filecache // 2, total_lowwmark)) + (sreclaim - min(sreclaim // 2, total_lowwmark))
available *= pgsize
print('mmstat =', mmstat)
print('total_lowwmark =', total_lowwmark)
print('total_reserved =', total_reserved)
print('sreclaim =', sreclaim)
print('filecache =', filecache)
print('available =', available)
assert available == mmstat['MemAvailable']