Fix macros.build-constraints' %limit_build

number of CPUs will never be set to less than 1
  this now outputs build flag overrides to be used with %make_build etc.
  add documentation

Signed-off-by: Michel Alexandre Salim <salimma@fedoraproject.org>

macros.build-constraints

@@ -1,10 +1,42 @@
 # Macros to constrain resource use during the build process
 
-# m: memory limit in MBs per core; default is 1024
+# outputs build flag overrides to be used in conjunction with
-%limit_build(m:) \
+# %%make_build, %%cmake_build etc.
-  _mem_per_process="%{-m:%{-m*}}%{!-m:1024}" \
+#
-  _max_mem=$(awk '/MemTotal/ { print $2 }' /proc/meminfo) \
+# if no override is needed, this macro outputs nothing
-  _max_jobs="$(($_max_mem / ($_mem_per_process * 1024)))" \
+#
-  _cur_max_jobs="%{_smp_build_ncpus}" \
+# - m   memory limit in MBs per core; default is 1024
-  test "${_cur_max_jobs}" -gt "${_max_jobs}" && _cur_max_jobs="${_max_jobs}" && echo "Warning: Reducing build parallelism to -j${_max_jobs} because of memory limits" \
+#
-  %global _smp_build_ncpus "${_cur_max_jobs}"
+# 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
+}

redhat-rpm-config.spec

@@ -6,7 +6,7 @@
 
 Summary: Red Hat specific rpm configuration files
 Name: redhat-rpm-config
-Version: 194
+Version: 195
 Release: 1%{?dist}
 # No version specified.
 License: GPL+
@@ -215,6 +215,12 @@ install -p -m 644 -t %{buildroot}%{_rpmluadir}/fedora/srpm forge.lua
 %{_rpmconfigdir}/macros.d/macros.kmp
 
 %changelog
+* Sun Aug 15 2021 Michel Alexandre Salim <salimma@fedoraproject.org> - 195-1
+- Fix macros.build-constraints' %%limit_build
+  - number of CPUs will never be set to less than 1
+  - this now outputs build flag overrides to be used with %%make_build etc.
+  - add documentation
+
 * Mon Aug  2 2021 Florian Weimer <fweimer@redhat.com> - 194-1
 - Active GCC plugin during LTO linking