Marcelo,
Anthony pointed out that you explicitly added this fallback in
618a568da4eda5c2e41fc4e58059546806afff6b. I'd like to know your
reasoning as to why - as noted below this causes problems for us, and
a situation where the fallback is desirable is not clear to me.
On Wed, Aug 01, 2012 at 02:41:05PM +1000, David Gibson wrote:
> When the -mem-path option is specified we try to allocate memory for guest
> RAM from mmap()ing files in the given path rather than from anonymous
> memory as usual. If we are unable to allocate memory from the path, we
> fall back to anonymous memory, with a rather cryptic error message.
>
> This fallback is a bad idea - if the user specified a backing path, they
> did so for a reason and falling back automatically could lead to confusing
> results.
>
> Under Book3S-HV KVM on PowerPC the failure is particularly bad, because the
> page size of the backing file limits what page sizes can be supported in the
> guest. We have code to automatically advertise the available page sizes to
> the guest, but this will give the wrong information in the case of a fall
> back to anonymous memory, because by the time we're producing that infor
> there's no easy way to determine that such a fallback occurred.
>
> Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
> ---
> exec.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index feb4795..544a090 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2425,7 +2425,6 @@ static void *file_ram_alloc(RAMBlock *block,
> area = mmap(0, memory, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
> #endif
> if (area == MAP_FAILED) {
> - perror("file_ram_alloc: can't mmap RAM pages");
> close(fd);
> return (NULL);
> }
> @@ -2528,8 +2527,9 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size,
> void *host,
> #if defined (__linux__) && !defined(TARGET_S390X)
> new_block->host = file_ram_alloc(new_block, size, mem_path);
> if (!new_block->host) {
> - new_block->host = qemu_vmalloc(size);
> - qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
> + fprintf(stderr, "Unable to map %llu bytes of RAM from
> requested"
> + " backing path %s\n", (unsigned long long)size,
> mem_path);
> + exit(1);
> }
> #else
> fprintf(stderr, "-mem-path option unsupported\n");
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
