[PATCH 1/2] kvm tools: Don't use all of host RAM for guests by default

[PATCH 1/2] kvm tools: Don't use all of host RAM for guests by default

[Pekka Enberg]

This patch fixes the default guest RAM size maximum to 80% of the host RAM to
avoid swapping the host to death.

Cc: Asias He <asias.hejun@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Prasad Joshi <prasadjoshi124@gmail.com>
Cc: Sasha Levin <levinsasha928@gmail.com>
Suggested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
---
 tools/kvm/kvm-run.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/tools/kvm/kvm-run.c b/tools/kvm/kvm-run.c
index ec1e462..b9cdec2 100644
--- a/tools/kvm/kvm-run.c
+++ b/tools/kvm/kvm-run.c
@@ -213,6 +213,12 @@ static void kernel_usage_with_options(void)
 	fprintf(stderr, "\nPlease see 'kvm run --help' for more options.\n\n");
 }
 
+/*
+ * If user didn't specify how much memory it wants to allocate for the guest,
+ * avoid filling the whole host RAM.
+ */
+#define RAM_SIZE_RATIO		0.8
+
 static u64 get_ram_size(int nr_cpus)
 {
 	long available;
@@ -226,7 +232,7 @@ static u64 get_ram_size(int nr_cpus)
 
 	page_size	= sysconf(_SC_PAGE_SIZE);
 
-	available	= (nr_pages * page_size) >> MB_SHIFT;
+	available	= ((nr_pages * page_size) >> MB_SHIFT) * RAM_SIZE_RATIO;
 
 	if (ram_size > available)
 		ram_size	= available;
-- 
1.7.0.4

[PATCH 2/2] kvm tools: Warn if guest RAM size exceeds host RAM size

[Pekka Enberg]

Guest memory size that's larger than host physical RAM can cause swap deaths on
the host so warn the user about it.

Cc: Asias He <asias.hejun@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Prasad Joshi <prasadjoshi124@gmail.com>
Cc: Sasha Levin <levinsasha928@gmail.com>
Suggested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
---
 tools/kvm/kvm-run.c |   23 ++++++++++++++++-------
 1 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/tools/kvm/kvm-run.c b/tools/kvm/kvm-run.c
index b9cdec2..764a242 100644
--- a/tools/kvm/kvm-run.c
+++ b/tools/kvm/kvm-run.c
@@ -213,6 +213,18 @@ static void kernel_usage_with_options(void)
 	fprintf(stderr, "\nPlease see 'kvm run --help' for more options.\n\n");
 }
 
+static u64 host_ram_size(void)
+{
+	long page_size;
+	long nr_pages;
+
+	nr_pages	= sysconf(_SC_PHYS_PAGES);
+
+	page_size	= sysconf(_SC_PAGE_SIZE);
+
+	return (nr_pages * page_size) >> MB_SHIFT;
+}
+
 /*
  * If user didn't specify how much memory it wants to allocate for the guest,
  * avoid filling the whole host RAM.
@@ -222,17 +234,11 @@ static void kernel_usage_with_options(void)
 static u64 get_ram_size(int nr_cpus)
 {
 	long available;
-	long page_size;
-	long nr_pages;
 	long ram_size;
 
 	ram_size	= 64 * (nr_cpus + 3);
 
-	nr_pages	= sysconf(_SC_PHYS_PAGES);
-
-	page_size	= sysconf(_SC_PAGE_SIZE);
-
-	available	= ((nr_pages * page_size) >> MB_SHIFT) * RAM_SIZE_RATIO;
+	available	= host_ram_size() * RAM_SIZE_RATIO;
 
 	if (ram_size > available)
 		ram_size	= available;
@@ -364,6 +370,9 @@ int kvm_cmd_run(int argc, const char **argv, const char *prefix)
 	if (ram_size < MIN_RAM_SIZE_MB)
 		die("Not enough memory specified: %lluMB (min %lluMB)", ram_size, MIN_RAM_SIZE_MB);
 
+	if (ram_size > host_ram_size())
+		warning("Guest memory size %lluMB exceeds host physical RAM size %lluMB", ram_size, host_ram_size());
+
 	ram_size <<= MB_SHIFT;
 
 	if (!kvm_dev)
-- 
1.7.0.4