From 5298551e07a9839c046e0987b325e03f8ba801e5 Mon Sep 17 00:00:00 2001
From: Eric Blake <eblake@redhat.com>
Date: Tue, 4 Oct 2011 09:44:25 -0600
Subject: [PATCH] init: raise default system aio limits

https://bugzilla.redhat.com/show_bug.cgi?id=740899 documents that
if qemu uses aio=native for its disks, then it consumes 128 aio
requests per disk.  On a host with multiple guests, this can quickly
run out of kernel aio requests with the default aio-max-nr of
65536.  Kernel developers have confirmed that there is no up-front
cost to raising this limit (a larger limit merely implies that more
aio requests can be issued in parallel, which in turn will result
in more kernel memory allocation, only if the system really does use
that many requests).  Since the system default limit prevents 256
disks, which is well within libvirt's current scalability, this
patch installs a file to raise the limit and document it in case a
system administrator has further cause to tune the limit.  The
install only works on platforms new enough to source /etc/sysctl.d/*
alongside /etc/sysctl.conf (F14 and RHEL 6).

* daemon/libvirtd.sysctl: New file.
* daemon/Makefile.am (EXTRA_DIST): Ship it.
(install-init, uninstall-init): Install it.
* libvirt.spec.in (%files): Include it in rpm.
---
 daemon/Makefile.am     | 11 ++++++++---
 daemon/libvirtd.sysctl |  8 ++++++++
 libvirt.spec.in        |  5 +++++
 3 files changed, 21 insertions(+), 3 deletions(-)
 create mode 100644 daemon/libvirtd.sysctl

diff --git a/daemon/Makefile.am b/daemon/Makefile.am
index 690bf851aa..1cf2b730b8 100644
--- a/daemon/Makefile.am
+++ b/daemon/Makefile.am
@@ -38,6 +38,7 @@ EXTRA_DIST =						\
 	libvirtd.policy-1				\
 	libvirtd.sasl					\
 	libvirtd.sysconf				\
+	libvirtd.sysctl					\
 	libvirtd.aug                                    \
 	libvirtd.logrotate.in                           \
 	libvirtd.qemu.logrotate.in                      \
@@ -252,16 +253,20 @@ install-logrotate: $(LOGROTATE_CONFS)
 
 if LIBVIRT_INIT_SCRIPT_RED_HAT
 install-init: libvirtd.init
-	mkdir -p $(DESTDIR)$(sysconfdir)/rc.d/init.d
+	mkdir -p $(DESTDIR)$(sysconfdir)/rc.d/init.d \
+	  $(DESTDIR)$(sysconfdir)/sysconfig \
+	  $(DESTDIR)$(sysconfdir)/sysctl.d
 	$(INSTALL_SCRIPT) libvirtd.init \
 	  $(DESTDIR)$(sysconfdir)/rc.d/init.d/libvirtd
-	mkdir -p $(DESTDIR)$(sysconfdir)/sysconfig
 	$(INSTALL_DATA) $(srcdir)/libvirtd.sysconf \
 	  $(DESTDIR)$(sysconfdir)/sysconfig/libvirtd
+	$(INSTALL_DATA) $(srcdir)/libvirtd.sysctl \
+	  $(DESTDIR)$(sysconfdir)/sysctl.d/libvirtd
 
 uninstall-init:
 	rm -f $(DESTDIR)$(sysconfdir)/rc.d/init.d/libvirtd \
-		$(DESTDIR)$(sysconfdir)/sysconfig/libvirtd
+		$(DESTDIR)$(sysconfdir)/sysconfig/libvirtd \
+		$(DESTDIR)$(sysconfdir)/sysctl.d/libvirtd
 
 BUILT_SOURCES += libvirtd.init
 
diff --git a/daemon/libvirtd.sysctl b/daemon/libvirtd.sysctl
new file mode 100644
index 0000000000..275482cc2e
--- /dev/null
+++ b/daemon/libvirtd.sysctl
@@ -0,0 +1,8 @@
+# The kernel allocates aio memory on demand, and this number limits the
+# number of parallel aio requests; the only drawback of a larger limit is
+# that a malicious guest could issue parallel requests to cause the kernel
+# to set aside memory.  Set this number at least as large as
+#   128 * (number of virtual disks on the host)
+# Libvirt uses a default of 1M requests to allow 8k disks, with at most
+# 64M of kernel memory if all disks hit an aio request at the same time.
+fs.aio-max-nr = 1048576
diff --git a/libvirt.spec.in b/libvirt.spec.in
index b87e3f6cb8..9f5797adae 100644
--- a/libvirt.spec.in
+++ b/libvirt.spec.in
@@ -962,6 +962,11 @@ fi
 %doc daemon/libvirtd.upstart
 %config(noreplace) %{_sysconfdir}/sysconfig/libvirtd
 %config(noreplace) %{_sysconfdir}/libvirt/libvirtd.conf
+%if 0%{?fedora} >= 14 || 0%{?rhel} >= 6
+%config(noreplace) %{_sysconfdir}/sysctl.d/libvirtd
+%else
+rm -f $RPM_BUILD_ROOT%{_sysconfdir}/sysctl.d/libvirtd
+%endif
 %if %{with_dtrace}
 %{_datadir}/systemtap/tapset/libvirtd.stp
 %endif
-- 
GitLab