Re: [PATCH v3] libxl: Wait for ballooning if free memory is increasing

[Ian Campbell <Ian.Campbell@citrix.com>]

On Fri, 2015-01-30 at 14:01 -0700, Mike Latimer wrote:
> During domain startup, all required memory ballooning must complete
> within a maximum window of 33 seconds (3 retries, 11 seconds of delay).
> If not, domain creation is aborted with a 'failed to free memory' error.
> 
> In order to accommodate large domains or slower hardware (which require
> substantially longer to balloon memory) the free memory process should
> continue retrying if the amount of free memory is increasing on each
> iteration of the loop.

Sorry for not spotting this earlier, but to accept a patch into the Xen
code base we need a Signed-off-by:
http://wiki.xen.org/wiki/Submitting_Xen_Patches#Signing_off_a_patch

You can provide one in this thread rather than resending if that is more
convenient.

For my part: Acked-by: Ian Campbell <ian.campbell@citrix.com>

> 
> ---
>  tools/libxl/xl_cmdimpl.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
> index 0b02a6c..9ff3c4f 100644
> --- a/tools/libxl/xl_cmdimpl.c
> +++ b/tools/libxl/xl_cmdimpl.c
> @@ -2194,8 +2194,9 @@ static int preserve_domain(uint32_t *r_domid, libxl_event *event,
>  
>  static int freemem(uint32_t domid, libxl_domain_build_info *b_info)
>  {
> -    int rc, retries = 3;
> -    uint32_t need_memkb, free_memkb;
> +    int rc, retries;
> +    const int MAX_RETRIES = 3;
> +    uint32_t need_memkb, free_memkb, free_memkb_prev = 0;
>  
>      if (!autoballoon)
>          return 0;
> @@ -2204,6 +2205,7 @@ static int freemem(uint32_t domid, libxl_domain_build_info *b_info)
>      if (rc < 0)
>          return rc;
>  
> +    retries = MAX_RETRIES;
>      do {
>          rc = libxl_get_free_memory(ctx, &free_memkb);
>          if (rc < 0)
> @@ -2228,7 +2230,16 @@ static int freemem(uint32_t domid, libxl_domain_build_info *b_info)
>          if (rc < 0)
>              return rc;
>  
> -        retries--;
> +        /*
> +         * If the amount of free mem has increased on this iteration (i.e.
> +         * some progress has been made) then reset the retry counter.
> +         */
> +        if (free_memkb > free_memkb_prev) {
> +            retries = MAX_RETRIES;
> +            free_memkb_prev = free_memkb;
> +        } else {
> +            retries--;
> +        }
>      } while (retries > 0);
>  
>      return ERROR_NOMEM;