On Wed, Oct 21, 2026 at 12:02 PM John Snow <[email protected]> wrote:
>
> On Wed, Oct 21, 2026 at 2:31 AM Gerd Hoffmann <[email protected]> wrote:
> >
> > Reduce memory footprint by mapping the kernel into memory instead of
> > reading into allocated memory in the common case (no -dtb $file on the
> > qemu command line).
> >
> > Cc: John Snow <[email protected]>
> > Signed-off-by: Gerd Hoffmann <[email protected]>
>
> Tested-by: John Snow <[email protected]>
>
Ping, is someone going to pick up this patch?
--js
> Using this patch, I shifted about 19MiB of resources from RssAnon to
> RssFile. This theoretically allows sharing resources between multiple
> QEMU instances in the trivial case using -kernel and -initrd. This
> matches how we already load initrd.
>
> --js
>
> > ---
> > hw/i386/x86-common.c | 25 ++++++++++++++++++++-----
> > 1 file changed, 20 insertions(+), 5 deletions(-)
> >
> > diff --git a/hw/i386/x86-common.c b/hw/i386/x86-common.c
> > index fa18bf1aeceb..25e141aa8537 100644
> > --- a/hw/i386/x86-common.c
> > +++ b/hw/i386/x86-common.c
> > @@ -911,16 +911,31 @@ void x86_load_linux(X86MachineState *x86ms,
> > }
> >
> > setup = g_malloc(setup_size);
> > - kernel = g_malloc(kernel_size);
> > fseek(f, 0, SEEK_SET);
> > if (fread(setup, 1, setup_size, f) != setup_size) {
> > fprintf(stderr, "fread() failed\n");
> > exit(1);
> > }
> > - fseek(f, 0, SEEK_SET);
> > - if (fread(kernel, 1, kernel_size, f) != kernel_size) {
> > - fprintf(stderr, "fread() failed\n");
> > - exit(1);
> > + if (dtb_filename) {
> > + /* read kernel into allocated memory, so we can realloc for the
> > dtb */
> > + kernel = g_malloc(kernel_size);
> > + fseek(f, 0, SEEK_SET);
> > + if (fread(kernel, 1, kernel_size, f) != kernel_size) {
> > + fprintf(stderr, "fread() failed\n");
> > + exit(1);
> > + }
> > + } else {
> > + /* mmap kernel */
> > + GMappedFile *mapped_file;
> > + GError *gerr = NULL;
> > +
> > + mapped_file = g_mapped_file_new(kernel_filename, false, &gerr);
> > + if (!mapped_file) {
> > + fprintf(stderr, "qemu: error reading kernel %s: %s\n",
> > + kernel_filename, gerr->message);
> > + exit(1);
> > + }
> > + kernel = (uint8_t *)g_mapped_file_get_contents(mapped_file);
> > }
> > fclose(f);
> >
> > --
> > 2.56.0
> >
