Re: [Qemu-devel] [PATCHv3 5/9] migration: search for zero instead of dup pages

[Eric Blake <eblake@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 1390 bytes --]

On 03/21/2013 09:57 AM, Peter Lieven wrote:
> virtually all dup pages are zero pages. remove
> the special is_dup_page() function and use the
> optimized buffer_find_nonzero_offset() function
> instead.
> 
> here buffer_find_nonzero_offset() is used directly
> to avoid the unnecssary additional checks in
> buffer_is_zero().
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---

> -    return 1;
> +    return 
> +     buffer_find_nonzero_offset(p, TARGET_PAGE_SIZE) == TARGET_PAGE_SIZE;

Unusual layout.  I would have written:

    return buffer_find_nonzero_offset(p, TARGET_PAGE_SIZE) ==
        TARGET_PAGE_SIZE;

>  /* struct contains XBZRLE cache and a static page
> @@ -443,7 +434,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
>  
>              /* In doubt sent page as normal */
>              bytes_sent = -1;
> -            if (is_dup_page(p)) {
> +            if (is_zero_page(p)) {
>                  acct_info.dup_pages++;
>                  bytes_sent = save_block_hdr(f, block, offset, cont,
>                                              RAM_SAVE_FLAG_COMPRESS);

I would move the change for qemu_put_byte(f, 0) out of patch 7 into this
patch, since this is the first point where you know the byte to send is 0.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 621 bytes --]