[Qemu-devel] Re: [PATCH 01/32] use anonymous memory for kqemu.

[Anthony Liguori <aliguori@us.ibm.com>]

The idea behind this patch is that currently kqemu uses /dev/shm for 
memory allocations instead of anonymous memory (like the rest of QEMU).  
Instead of introducing YA hook, we can just switch kqemu to use 
anonymous memory and eliminate the special case.

If I recall correctly, the reason for using /dev/shm was concern that 
get_user_pages() didn't do the right thing for anonymous memory and the 
use of /dev/shm was a hack around that.  However, I'm not sure that was 
ever the case.  Certainly, with any sufficiently modern kernel 
get_user_pages() does what one would expect.  KVM uses get_user_pages() 
on anonymous memory in roughly the same way kqemu uses it now.

So I think it's safe to make the switch.  Fabrice, what do you think?

Regards,

Anthony Liguori

Glauber Costa wrote:
> Signed-off-by: Glauber Costa <glommer@redhat.com>
> ---
>  osdep.c |  111 ---------------------------------------------------------------
>  1 files changed, 0 insertions(+), 111 deletions(-)
>
> diff --git a/osdep.c b/osdep.c
> index 683aad0..31c96e6 100644
> --- a/osdep.c
> +++ b/osdep.c
> @@ -68,112 +68,9 @@ void qemu_vfree(void *ptr)
>
>  #else
>
> -#if defined(USE_KQEMU)
> -
> -#ifdef __OpenBSD__
> -#include <sys/param.h>
> -#include <sys/types.h>
> -#include <sys/mount.h>
> -#else
> -#include <sys/vfs.h>
> -#endif
> -
>  #include <sys/mman.h>
>  #include <fcntl.h>
>
> -static void *kqemu_vmalloc(size_t size)
> -{
> -    static int phys_ram_fd = -1;
> -    static int phys_ram_size = 0;
> -    void *ptr;
> -
> -#ifdef __OpenBSD__ /* no need (?) for a dummy file on OpenBSD */
> -    int map_anon = MAP_ANON;
> -#else
> -    int map_anon = 0;
> -    const char *tmpdir;
> -    char phys_ram_file[1024];
> -#ifdef HOST_SOLARIS
> -    struct statvfs stfs;
> -#else
> -    struct statfs stfs;
> -#endif
> -
> -    if (phys_ram_fd < 0) {
> -        tmpdir = getenv("QEMU_TMPDIR");
> -        if (!tmpdir)
> -#ifdef HOST_SOLARIS
> -            tmpdir = "/tmp";
> -        if (statvfs(tmpdir, &stfs) == 0) {
> -#else
> -            tmpdir = "/dev/shm";
> -        if (statfs(tmpdir, &stfs) == 0) {
> -#endif
> -            int64_t free_space;
> -            int ram_mb;
> -
> -            free_space = (int64_t)stfs.f_bavail * stfs.f_bsize;
> -            if ((ram_size + 8192 * 1024) >= free_space) {
> -                ram_mb = (ram_size / (1024 * 1024));
> -                fprintf(stderr,
> -                        "You do not have enough space in '%s' for the %d MB of QEMU virtual RAM.\n",
> -                        tmpdir, ram_mb);
> -                if (strcmp(tmpdir, "/dev/shm") == 0) {
> -                    fprintf(stderr, "To have more space available provided you have enough RAM and swap, do as root:\n"
> -                            "mount -o remount,size=%dm /dev/shm\n",
> -                            ram_mb + 16);
> -                } else {
> -                    fprintf(stderr,
> -                            "Use the '-m' option of QEMU to diminish the amount of virtual RAM or use the\n"
> -                            "QEMU_TMPDIR environment variable to set another directory where the QEMU\n"
> -                            "temporary RAM file will be opened.\n");
> -                }
> -                fprintf(stderr, "Or disable the accelerator module with -no-kqemu\n");
> -                exit(1);
> -            }
> -        }
> -        snprintf(phys_ram_file, sizeof(phys_ram_file), "%s/qemuXXXXXX",
> -                 tmpdir);
> -        phys_ram_fd = mkstemp(phys_ram_file);
> -        if (phys_ram_fd < 0) {
> -            fprintf(stderr,
> -                    "warning: could not create temporary file in '%s'.\n"
> -                    "Use QEMU_TMPDIR to select a directory in a tmpfs filesystem.\n"
> -                    "Using '/tmp' as fallback.\n",
> -                    tmpdir);
> -            snprintf(phys_ram_file, sizeof(phys_ram_file), "%s/qemuXXXXXX",
> -                     "/tmp");
> -            phys_ram_fd = mkstemp(phys_ram_file);
> -            if (phys_ram_fd < 0) {
> -                fprintf(stderr, "Could not create temporary memory file '%s'\n",
> -                        phys_ram_file);
> -                exit(1);
> -            }
> -        }
> -        unlink(phys_ram_file);
> -    }
> -    size = (size + 4095) & ~4095;
> -    ftruncate(phys_ram_fd, phys_ram_size + size);
> -#endif /* !__OpenBSD__ */
> -    ptr = mmap(NULL,
> -               size,
> -               PROT_WRITE | PROT_READ, map_anon | MAP_SHARED,
> -               phys_ram_fd, phys_ram_size);
> -    if (ptr == MAP_FAILED) {
> -        fprintf(stderr, "Could not map physical memory\n");
> -        exit(1);
> -    }
> -    phys_ram_size += size;
> -    return ptr;
> -}
> -
> -static void kqemu_vfree(void *ptr)
> -{
> -    /* may be useful some day, but currently we do not need to free */
> -}
> -
> -#endif
> -
>  void *qemu_memalign(size_t alignment, size_t size)
>  {
>  #if defined(_POSIX_C_SOURCE)
> @@ -193,10 +90,6 @@ void *qemu_memalign(size_t alignment, size_t size)
>  /* alloc shared memory pages */
>  void *qemu_vmalloc(size_t size)
>  {
> -#if defined(USE_KQEMU)
> -    if (kqemu_allowed)
> -        return kqemu_vmalloc(size);
> -#endif
>  #ifdef _BSD
>      return valloc(size);
>  #else
> @@ -206,10 +99,6 @@ void *qemu_vmalloc(size_t size)
>
>  void qemu_vfree(void *ptr)
>  {
> -#if defined(USE_KQEMU)
> -    if (kqemu_allowed)
> -        kqemu_vfree(ptr);
> -#endif
>      free(ptr);
>  }
>
>