From daac8f3d73722b2547d4e6b702c2cb221a6f7912 Mon Sep 17 00:00:00 2001
From: Matthias Klose <doko@ubuntu.com>
Date: Wed, 18 Oct 2023 15:13:57 +0200
Subject: [PATCH]   [ Matthias Klose ]   * Limit the number of parallel
 processes based on the available memory     and the packages to be built
 (flang has some memory hogs).

---
 debian/changelog |  8 ++++++++
 debian/rules     | 30 +++++++++++++++++++++---------
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/debian/changelog b/debian/changelog
index d2b69887..84c821ea 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,11 @@
+llvm-toolchain-17 (1:17.0.3-1~exp2) UNRELEASED; urgency=medium
+
+  [ Matthias Klose ]
+  * Limit the number of parallel processes based on the available memory
+    and the packages to be built (flang has some memory hogs).
+
+ -- Matthias Klose <doko@debian.org>  Wed, 18 Oct 2023 15:00:25 +0200
+
 llvm-toolchain-17 (1:17.0.3-1~exp1) experimental; urgency=medium
 
   [ Matthias Klose ]
diff --git a/debian/rules b/debian/rules
index 43883ba2..cb65d3f9 100755
--- a/debian/rules
+++ b/debian/rules
@@ -27,27 +27,38 @@ else
   BRANCH_NAME=$(LLVM_VERSION)
 endif
 
+VENDOR=$(shell lsb_release -is)
+DISTRO=$(shell lsb_release -sc)
+
 SONAME_EXT      := 1
 SONAME_OPENMP	:= 5
 # Manage the case when the version is 3.5~svn213052-1~exp1 or 3.4.2-1
 DEBIAN_REVISION := $(shell dpkg-parsechangelog |  sed -rne "s,^Version: 1:([0-9.]+)(~|-)(.*),\3,p")
 ifneq (,$(filter parallel=%,$(subst $(COMMA), ,$(DEB_BUILD_OPTIONS))))
-  NJOBS := $(subst parallel=,,$(filter parallel=%,$(subst $(COMMA), ,$(DEB_BUILD_OPTIONS))))
+  NCPUS := $(subst parallel=,,$(filter parallel=%,$(subst $(COMMA), ,$(DEB_BUILD_OPTIONS))))
 else
-  NJOBS := $(shell nproc)
+  NCPUS := $(shell nproc)
 endif
 
-VENDOR=$(shell lsb_release -is)
-DISTRO=$(shell lsb_release -sc)
-
-DH_VERSION := $(shell dpkg -s debhelper | grep '^Version' | awk '{print $$2}')
-
-include /usr/share/dpkg/architecture.mk
-
 # this contains all packages to be built. Note that for at least the clean target,
 # this always includes the binary-indep packages.
 packages := $(shell dh_listpackages)
 
+# flang has some memory hogs, of up to 6.2gb per process. Limit the parallel jobs
+# based on the available memory
+ifneq (,$(filter flang-$(LLVM_VERSION), $(packages)))
+  MEM_PER_CPU=3900
+else
+  MEM_PER_CPU=2100
+endif
+NJOBS := $(shell mt=`awk '/^MemTotal/ { print $$2 }' /proc/meminfo`; \
+		awk -vn=$(NCPUS) -vmt=$$mt -vm=$(MEM_PER_CPU) \
+		  'END { mt/=1024; n2 = int(mt/m); print n==1 ? 1 : n2<n+1 ? n2 : n+1}' < /dev/null)
+
+DH_VERSION := $(shell dpkg -s debhelper | grep '^Version' | awk '{print $$2}')
+
+include /usr/share/dpkg/architecture.mk
+
 CONFIGURE_EXTRA =
 
 # dpkg-buildflags support
@@ -546,6 +557,7 @@ stamps/preconfigure:
 		echo "  No memory info available"; \
 	fi
 	@echo "Processors: $$(cat /proc/cpuinfo | grep --count '^processor')"
+	@echo "Used Processors: $(NJOBS) (out of $(NCPUS)), $(MEM_PER_CPU)kb/processor"
 
 	@echo "DEB_BUILD_OPTIONS=$(DEB_BUILD_OPTIONS)"
 	@echo "DEB_HOST_MULTIARCH=$(DEB_HOST_MULTIARCH)"