[build] force Linux to drop cache before calling kvm (sonic-net#2717)

* [vm build] force Linux to drop cache before calling kvm

KVM need to allocate 2G memory for this build. The system memory might
be occupied by cache at the moment and doesn't have 2G chunk to give
out. Forcing Kernel to drop cache to boost the chance of getting 2G
memory.

Signed-off-by: Ying Xie <ying.xie@microsoft.com>

* [make] add option to enable/disable VS build memory preparation

Signed-off-by: Ying Xie <ying.xie@microsoft.com>

Makefile.work

@@ -27,6 +27,9 @@
 #  *                  make NOSTRETCH=1 KEEP_SLAVE_ON=yes <any jessie target>
 #  * SOURCE_FOLDER: host path to be mount as /var/$(USER)/src, only effective when KEEP_SLAVE_ON=yes
 #  * SONIC_BUILD_JOBS: Specifying number of concurrent build job(s) to run
+#  * VS_PREPARE_MEM: Prepare memory in VS build (drop cache and compact).
+#  *                 Default: yes
+#  *                 Values:  yes, no
 #  * KERNEL_PROCURE_METHOD: Specifying method of obtaining kernel Debian package: download or build
 #
 ###############################################################################
@@ -114,6 +117,7 @@ SONIC_BUILD_INSTRUCTION :=  make \
                            PASSWORD=$(PASSWORD) \
                            USERNAME=$(USERNAME) \
                            SONIC_BUILD_JOBS=$(SONIC_BUILD_JOBS) \
+                           VS_PREPARE_MEM=$(VS_PREPARE_MEM) \
                            KERNEL_PROCURE_METHOD=$(KERNEL_PROCURE_METHOD) \
                            HTTP_PROXY=$(http_proxy) \
                            HTTPS_PROXY=$(https_proxy) \

build_kvm_image.sh

@@ -1,4 +1,4 @@
-#!/bin/sh -ex
+#!/bin/bash -ex
 
 #  Copyright (C) 2014 Curt Brune <curt@cumulusnetworks.com>
 #
@@ -47,6 +47,15 @@ prepare_installer_disk()
 create_disk
 prepare_installer_disk
 
+echo "Prepare memory for KVM build: $vs_build_prepare_mem"
+free -m
+if [[ "$vs_build_prepare_mem" == "yes" ]]; then
+    # Force o.s. to drop cache and compact memory so that KVM can get 2G memory
+    sudo bash -c 'echo 1 > /proc/sys/vm/drop_caches'
+    sudo bash -c 'echo 1 > /proc/sys/vm/compact_memory'
+    free -m
+fi
+
 /usr/bin/kvm -m $MEM \
     -name "onie" \
     -boot "order=cd,once=d" -cdrom "$ONIE_RECOVERY_ISO" \

rules/config

@@ -84,3 +84,6 @@ DEFAULT_KERNEL_PROCURE_METHOD = build
 # group during installation.
 FRR_USER_UID = 1000
 FRR_USER_GID = 1000
+
+# Default VS build memory preparation
+DEFAULT_VS_PREPARE_MEM = yes

slave.mk

@@ -109,6 +109,10 @@ ifeq ($(SONIC_BUILD_JOBS),)
 override SONIC_BUILD_JOBS := $(SONIC_CONFIG_BUILD_JOBS)
 endif
 
+ifeq ($(VS_PREPARE_MEM),)
+override VS_PREPARE_MEM := $(DEFAULT_VS_PREPARE_MEM)
+endif
+
 ifeq ($(KERNEL_PROCURE_METHOD),)
 override KERNEL_PROCURE_METHOD := $(DEFAULT_KERNEL_PROCURE_METHOD)
 endif
@@ -155,6 +159,7 @@ $(info "SONIC_DEBUGGING_ON"              : "$(SONIC_DEBUGGING_ON)")
 $(info "SONIC_PROFILING_ON"              : "$(SONIC_PROFILING_ON)")
 $(info "KERNEL_PROCURE_METHOD"           : "$(KERNEL_PROCURE_METHOD)")
 $(info "BUILD_TIMESTAMP"                 : "$(BUILD_TIMESTAMP)")
+$(info "VS_PREPARE_MEM"                  : "$(VS_PREPARE_MEM)")
 $(info )
 
 ###############################################################################
@@ -163,6 +168,7 @@ $(info )
 ###############################################################################
 
 export kernel_procure_method=$(KERNEL_PROCURE_METHOD)
+export vs_build_prepare_mem=$(VS_PREPARE_MEM)
 
 ###############################################################################
 ## Local targets