kvm tools: Scale guest RAM size by CPU count

This patch increases default RAM size to 256 for one CPU and introduces RAM
size linear scaling based on CPUs as suggested by Ingo Molnar:

     64MB*(nr_cpus + 3)

     ------------------
       1 CPUs:   256 MB
       2 CPUs:   320 MB
       3 CPUs:   384 MB
       4 CPUs:   448 MB
       5 CPUs:   512 MB
       6 CPUs:   576 MB
       7 CPUs:   640 MB
       8 CPUs:   704 MB
       9 CPUs:   768 MB
      10 CPUs:   832 MB
      11 CPUs:   896 MB
      12 CPUs:   960 MB
      13 CPUs:  1024 MB
      14 CPUs:  1088 MB
      15 CPUs:  1152 MB
      16 CPUs:  1216 MB

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>

diff --git a/tools/kvm/kvm-run.c b/tools/kvm/kvm-run.c
index 2ff126d5c746c1ff8e9c93e5c4b0e0f34ccd9df3..2504ab02a85e54f906d6ce8e79b4910a52871b82 100644 (file)
--- a/tools/kvm/kvm-run.c
+++ b/tools/kvm/kvm-run.c
@@ -46,7 +46,7 @@ static struct kvm *kvm;
 static struct kvm_cpu *kvm_cpus[KVM_NR_CPUS];
 static __thread struct kvm_cpu *current_kvm_cpu;
 
-static u64 ram_size = MIN_RAM_SIZE_MB;
+static u64 ram_size;
 static u8  image_count;
 static const char *kernel_cmdline;
 static const char *kernel_filename;
@@ -213,6 +213,27 @@ static void kernel_usage_with_options(void)
        fprintf(stderr, "\nPlease see 'kvm run --help' for more options.\n\n");
 }
 
+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;
+
+       if (ram_size > available)
+               ram_size        = available;
+
+       return ram_size;
+}
+
 static const char *find_kernel(void)
 {
        const char **k;
@@ -330,6 +351,9 @@ int kvm_cmd_run(int argc, const char **argv, const char *prefix)
        if (nrcpus < 1 || nrcpus > KVM_NR_CPUS)
                die("Number of CPUs %d is out of [1;%d] range", nrcpus, KVM_NR_CPUS);
 
+       if (!ram_size)
+               ram_size        = get_ram_size(nrcpus);
+
        if (ram_size < MIN_RAM_SIZE_MB)
                die("Not enough memory specified: %lluMB (min %lluMB)", ram_size, MIN_RAM_SIZE_MB);