Re: [Qemu-devel] [PULL 49/57] Round up RAMBlock sizes to host page sizes

[Peter Crosthwaite]

On Tue, Nov 10, 2015 at 6:25 AM, Juan Quintela <address@hidden> wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> RAMBlocks that are not a multiple of host pages in length
> cause problems for postcopy (I've seen an ACPI table on aarch64
> be 5k in length - i.e. 5x target-page), so round RAMBlock sizes
> up to a host-page.
>
> This potentially breaks migration compatibility due to changes
> in RAMBlock sizes; however:
>    1) x86 and s390 I think always have host=target page size
>    2) When I've tried on Power the block sizes already seem aligned.
>    3) I don't think there's anything else that maintains per-version
>       machine-types for compatibility.
>

Is there any reason this shouldn't be converted to
REAL_HOST_PAGE_ALIGN given these restrictions?

I'm thinking about multi-arch, where HOST_PAGE_ALIGN is inaccessible
from exec.c as it is target-arch specific. My previous workaround was
to define the target page size for multi-arch so that TARGET_PAGE_SIZE
was usable but not sure that should go viral to these other defs.

The other approach, is to calculate the lowest common denominator for
the page size accross the multi-arch targets (+ the host) for the
implementation of HOST_PAGE_ALIGN and friends.

Regards,
Peter

> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> Reviewed-by: Juan Quintela <address@hidden>
> Signed-off-by: Juan Quintela <address@hidden>
> ---
>  exec.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index 36886ee..b09f18b 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1452,7 +1452,7 @@ int qemu_ram_resize(ram_addr_t base, ram_addr_t 
> newsize, Error **errp)
>
>      assert(block);
>
> -    newsize = TARGET_PAGE_ALIGN(newsize);
> +    newsize = HOST_PAGE_ALIGN(newsize);
>
>      if (block->used_length == newsize) {
>          return 0;
> @@ -1596,7 +1596,7 @@ ram_addr_t qemu_ram_alloc_from_file(ram_addr_t size, 
> MemoryRegion *mr,
>          return -1;
>      }
>
> -    size = TARGET_PAGE_ALIGN(size);
> +    size = HOST_PAGE_ALIGN(size);
>      new_block = g_malloc0(sizeof(*new_block));
>      new_block->mr = mr;
>      new_block->used_length = size;
> @@ -1632,8 +1632,8 @@ ram_addr_t qemu_ram_alloc_internal(ram_addr_t size, 
> ram_addr_t max_size,
>      ram_addr_t addr;
>      Error *local_err = NULL;
>
> -    size = TARGET_PAGE_ALIGN(size);
> -    max_size = TARGET_PAGE_ALIGN(max_size);
> +    size = HOST_PAGE_ALIGN(size);
> +    max_size = HOST_PAGE_ALIGN(max_size);
>      new_block = g_malloc0(sizeof(*new_block));
>      new_block->mr = mr;
>      new_block->resized = resized;
> --
> 2.5.0
>
>