rcutorture: Make kvm.sh allow more memory for --kasan runs

KASAN allots significant memory to track allocation state, and the amount
of memory has increased recently, which results in frequent OOMs on a
few of the rcutorture scenarios.  This commit therefore provides 2G of
memory for --kasan runs, up from the 512M default.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/rcutorture/bin/kvm.sh

@@ -44,6 +44,7 @@ TORTURE_KCONFIG_KASAN_ARG=""
 TORTURE_KCONFIG_KCSAN_ARG=""
 TORTURE_KMAKE_ARG=""
 TORTURE_QEMU_MEM=512
+torture_qemu_mem_default=1
 TORTURE_REMOTE=
 TORTURE_SHUTDOWN_GRACE=180
 TORTURE_SUITE=rcu
@@ -180,6 +181,10 @@ do
 		;;
 	--kasan)
 		TORTURE_KCONFIG_KASAN_ARG="CONFIG_DEBUG_INFO=y CONFIG_KASAN=y"; export TORTURE_KCONFIG_KASAN_ARG
+		if test -n "$torture_qemu_mem_default"
+		then
+			TORTURE_QEMU_MEM=2G
+		fi
 		;;
 	--kconfig|--kconfigs)
 		checkarg --kconfig "(Kconfig options)" $# "$2" '^CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\( CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\)*$' '^error$'
@@ -202,6 +207,7 @@ do
 	--memory)
 		checkarg --memory "(memory size)" $# "$2" '^[0-9]\+[MG]\?$' error
 		TORTURE_QEMU_MEM=$2
+		torture_qemu_mem_default=
 		shift
 		;;
 	--no-initrd)