Re: [Xen-devel] [PATCH Remus v1 2/8] tools/libxc: reuse send_some_pages() in send_all_pages()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 07/05/15 07:37, Yang Hongyang wrote:
> introduce bitmap_set() to set the entire bitmap.
> in send_all_pages(), set the entire bitmap and call send_some_pages().
>
> Signed-off-by: Yang Hongyang <yanghy@xxxxxxxxxxxxxx>

Ah - I see now why you unconditionally allocated the to_send bitmap.

I suppose it is probably better to have less divergence between the live
and non-live cases, and the size of the bitmap is substantially less
than other structures in use.

In which case, can I suggest the following which partially supersedes my
review in patch 1.

* Instead of having the bitmap called "to_send", having it called
something more appropriate like "dirty_bitmap".
* s/send_some_pages/send_dirty_pages/ and drop the *bitmap parameter. 
('entries' should stay as it is a useful sanity check).

This way, send_all_page() logically sets all pages as dirty, then sends
any dirty pages.

~Andrew

> ---
>  tools/libxc/xc_bitops.h  |  5 +++++
>  tools/libxc/xc_sr_save.c | 41 +++++++++++------------------------------
>  2 files changed, 16 insertions(+), 30 deletions(-)
>
> diff --git a/tools/libxc/xc_bitops.h b/tools/libxc/xc_bitops.h
> index dfce3b8..cd749f4 100644
> --- a/tools/libxc/xc_bitops.h
> +++ b/tools/libxc/xc_bitops.h
> @@ -26,6 +26,11 @@ static inline unsigned long *bitmap_alloc(int nr_bits)
>      return calloc(1, bitmap_size(nr_bits));
>  }
>  
> +static inline void bitmap_set(unsigned long *addr, int nr_bits)
> +{
> +    memset(addr, 0xff, bitmap_size(nr_bits));
> +}
> +
>  static inline void bitmap_clear(unsigned long *addr, int nr_bits)
>  {
>      memset(addr, 0, bitmap_size(nr_bits));
> diff --git a/tools/libxc/xc_sr_save.c b/tools/libxc/xc_sr_save.c
> index 7fed668..2993ec3 100644
> --- a/tools/libxc/xc_sr_save.c
> +++ b/tools/libxc/xc_sr_save.c
> @@ -346,36 +346,6 @@ static int suspend_domain(struct xc_sr_context *ctx)
>  }
>  
>  /*
> - * Send all pages in the guests p2m.  Used as the first iteration of the live
> - * migration loop, and for a non-live save.
> - */
> -static int send_all_pages(struct xc_sr_context *ctx)
> -{
> -    xc_interface *xch = ctx->xch;
> -    xen_pfn_t p;
> -    int rc;
> -
> -    for ( p = 0; p < ctx->save.p2m_size; ++p )
> -    {
> -        rc = add_to_batch(ctx, p);
> -        if ( rc )
> -            return rc;
> -
> -        /* Update progress every 4MB worth of memory sent. */
> -        if ( (p & ((1U << (22 - 12)) - 1)) == 0 )
> -            xc_report_progress_step(xch, p, ctx->save.p2m_size);
> -    }
> -
> -    rc = flush_batch(ctx);
> -    if ( rc )
> -        return rc;
> -
> -    xc_report_progress_step(xch, ctx->save.p2m_size,
> -                            ctx->save.p2m_size);
> -    return 0;
> -}
> -
> -/*
>   * Send a subset of pages in the guests p2m, according to the provided 
> bitmap.
>   * Used for each subsequent iteration of the live migration loop.
>   *
> @@ -417,6 +387,17 @@ static int send_some_pages(struct xc_sr_context *ctx,
>      return 0;
>  }
>  
> +/*
> + * Send all pages in the guests p2m.  Used as the first iteration of the live
> + * migration loop, and for a non-live save.
> + */
> +static int send_all_pages(struct xc_sr_context *ctx)
> +{
> +    bitmap_set(to_send, ctx->save.p2m_size);
> +
> +    return send_some_pages(ctx, to_send, ctx->save.p2m_size);
> +}
> +
>  static int enable_logdirty(struct xc_sr_context *ctx)
>  {
>      xc_interface *xch = ctx->xch;


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