redhat-rpm-config/macros.build-constraints

# Macros to constrain resource use during the build process

# Changes _smp_build_ncpus depending on various factors
#
# -c cpus  constrains the CPU count to "cpus"
# -m mem   constrains the CPU count to the total amount of memory in the system
#          (in megabytes) divided by "mem", rounded down
#
# If no options are passed, sets _smp_build_ncpus to 1.
# _smp_build_ncpus will never be raised, only lowered.
%constrain_build(c:m:) %{lua:

  -- Check a value and clamp it to at least 1
  local function check_and_clamp(v, string)
    if v == nil then return nil end

    i = math.tointeger(v)
    if i == nil then
      macros.error({"%%%0: invalid "..string.." value "..v})
      return nil
    end

    local clamp = math.max(1, math.floor(i))
    if i ~= clamp then
      macros.error({"%%%0: invalid "..string.." value "..v})
      return nil
    end
    return clamp
  end

  -- Parse meminfo to find the total amount of memory in the system
  local function getmem()
    local mem = 0
    for l in io.lines('/proc/meminfo') do
      if l:sub(1, 9) == "MemTotal:" then
        mem = math.tointeger(string.match(l, "MemTotal:%s+(%d+)"))
        break
      end
    end
    return mem
  end

  local mem_limit = check_and_clamp(opt.m, "mem limit")
  local cpu_limit = check_and_clamp(opt.c, "cpu limit")
  local current_cpus = math.tointeger(macros._smp_build_ncpus)
  local constrained_cpus = current_cpus

  if (not cpu_limit and not mem_limit) then
    cpu_limit = 1
  end

  if cpu_limit ~= nil then
    constrained_cpus = math.min(cpu_limit, constrained_cpus)
  end
  if mem_limit ~= nil then
    local mem_total = getmem(verbose)
    local limit = math.max(1, mem_total // (mem_limit * 1024))
    constrained_cpus = math.min(constrained_cpus, limit)
  end

  macros._smp_build_ncpus = constrained_cpus
}

# outputs build flag overrides to be used in conjunction with
# %%make_build, %%cmake_build etc.
#
# if no override is needed, this macro outputs nothing
#
# - m   memory limit in MBs per core; default is 1024
#
# Usage:
# e.g. %make_build %{limit_build -m 2048}
#   => /usr/bin/make -O -j16 V=1 VERBOSE=1
#      %make_build %{limit_build -m 40960}
#   => /usr/bin/make -O -j16 V=1 VERBOSE=1 -j1
# 
%limit_build(m:) %{lua:
  local mem_per_process=rpm.expand("%{-m*}")
  if mem_per_process == "" then
    mem_per_process = 1024
  else
    mem_per_process = tonumber(mem_per_process)
  end
  local mem_total = 0
  for line in io.lines('/proc/meminfo') do
    if line:sub(1, 9) == "MemTotal:" then
      local tokens = {}
      for token in line:gmatch("%w+") do
        tokens[#tokens + 1] = token
      end
      mem_total = tonumber(tokens[2])
      break
    end
  end
  local max_jobs = mem_total // (mem_per_process * 1024)
  if max_jobs < 1 then
    max_jobs = 1
  end
  cur_max_jobs=tonumber(rpm.expand("%{_smp_build_ncpus}"))
  if cur_max_jobs > max_jobs then
    print("-j" .. max_jobs)
  end
}