In order to reduce the memory footprint we map into memory
the initrd using g_mapped_file_new() instead of reading it.
In this way we can share the initrd pages between multiple
instances of QEMU.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 hw/i386/pc.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 549c437050..b139589777 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1241,17 +1241,20 @@ static void load_linux(PCMachineState *pcms,
 
             /* load initrd */
             if (initrd_filename) {
+                GMappedFile *gmf;
                 gsize initrd_size;
                 gchar *initrd_data;
                 GError *gerr = NULL;
 
-                if (!g_file_get_contents(initrd_filename, &initrd_data,
-                            &initrd_size, &gerr)) {
+                gmf = g_mapped_file_new(initrd_filename, false, &gerr);
+                if (!gmf) {
                     fprintf(stderr, "qemu: error reading initrd %s: %s\n",
                             initrd_filename, gerr->message);
                     exit(1);
                 }
 
+                initrd_data = g_mapped_file_get_contents(gmf);
+                initrd_size = g_mapped_file_get_length(gmf);
                 initrd_max = pcms->below_4g_mem_size - pcmc->acpi_data_size - 1;
                 if (initrd_size >= initrd_max) {
                     fprintf(stderr, "qemu: initrd is too large, cannot support."
@@ -1378,6 +1381,7 @@ static void load_linux(PCMachineState *pcms,
 
     /* load initrd */
     if (initrd_filename) {
+        GMappedFile *gmf;
         gsize initrd_size;
         gchar *initrd_data;
         GError *gerr = NULL;
@@ -1387,12 +1391,15 @@ static void load_linux(PCMachineState *pcms,
             exit(1);
         }
 
-        if (!g_file_get_contents(initrd_filename, &initrd_data,
-                                 &initrd_size, &gerr)) {
+        gmf = g_mapped_file_new(initrd_filename, false, &gerr);
+        if (!gmf) {
             fprintf(stderr, "qemu: error reading initrd %s: %s\n",
                     initrd_filename, gerr->message);
             exit(1);
         }
+
+        initrd_data = g_mapped_file_get_contents(gmf);
+        initrd_size = g_mapped_file_get_length(gmf);
         if (initrd_size >= initrd_max) {
             fprintf(stderr, "qemu: initrd is too large, cannot support."
                     "(max: %"PRIu32", need %"PRId64")\n",
-- 
2.20.1

On 23/07/19 16:04, Stefano Garzarella wrote:
> In order to reduce the memory footprint we map into memory
> the initrd using g_mapped_file_new() instead of reading it.
> In this way we can share the initrd pages between multiple
> instances of QEMU.
> 
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Coverity is going to complain about the leaks.  Should we instead store
the initrd GMappedFile in PCMachineState, even if it is just for reference?

Paolo

> ---
>  hw/i386/pc.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 549c437050..b139589777 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1241,17 +1241,20 @@ static void load_linux(PCMachineState *pcms,
>  
>              /* load initrd */
>              if (initrd_filename) {
> +                GMappedFile *gmf;
>                  gsize initrd_size;
>                  gchar *initrd_data;
>                  GError *gerr = NULL;
>  
> -                if (!g_file_get_contents(initrd_filename, &initrd_data,
> -                            &initrd_size, &gerr)) {
> +                gmf = g_mapped_file_new(initrd_filename, false, &gerr);
> +                if (!gmf) {
>                      fprintf(stderr, "qemu: error reading initrd %s: %s\n",
>                              initrd_filename, gerr->message);
>                      exit(1);
>                  }
>  
> +                initrd_data = g_mapped_file_get_contents(gmf);
> +                initrd_size = g_mapped_file_get_length(gmf);
>                  initrd_max = pcms->below_4g_mem_size - pcmc->acpi_data_size - 1;
>                  if (initrd_size >= initrd_max) {
>                      fprintf(stderr, "qemu: initrd is too large, cannot support."
> @@ -1378,6 +1381,7 @@ static void load_linux(PCMachineState *pcms,
>  
>      /* load initrd */
>      if (initrd_filename) {
> +        GMappedFile *gmf;
>          gsize initrd_size;
>          gchar *initrd_data;
>          GError *gerr = NULL;
> @@ -1387,12 +1391,15 @@ static void load_linux(PCMachineState *pcms,
>              exit(1);
>          }
>  
> -        if (!g_file_get_contents(initrd_filename, &initrd_data,
> -                                 &initrd_size, &gerr)) {
> +        gmf = g_mapped_file_new(initrd_filename, false, &gerr);
> +        if (!gmf) {
>              fprintf(stderr, "qemu: error reading initrd %s: %s\n",
>                      initrd_filename, gerr->message);
>              exit(1);
>          }
> +
> +        initrd_data = g_mapped_file_get_contents(gmf);
> +        initrd_size = g_mapped_file_get_length(gmf);
>          if (initrd_size >= initrd_max) {
>              fprintf(stderr, "qemu: initrd is too large, cannot support."
>                      "(max: %"PRIu32", need %"PRId64")\n",
> 

On Tue, Jul 23, 2019 at 04:30:17PM +0200, Paolo Bonzini wrote:
> On 23/07/19 16:04, Stefano Garzarella wrote:
> > In order to reduce the memory footprint we map into memory
> > the initrd using g_mapped_file_new() instead of reading it.
> > In this way we can share the initrd pages between multiple
> > instances of QEMU.
> > 
> > Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> > Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> 
> Coverity is going to complain about the leaks.  Should we instead store
> the initrd GMappedFile in PCMachineState, even if it is just for reference?
> 

Yes, I'll put it in the PCMachineState.

Thanks,
Stefano