Re: xl mem-max error

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

On Mon, 2014-11-10 at 10:38 -0500, Zhigang Wang wrote:
> OK. Let me try my best:
> 
> >>> I'm confused by the description of what's going on, in particular the
> >>> mixing of mem-max commands and target xenstore nodes (since the former
> >>> doesn't really affect the latter).
> >>>
> >>> How was the domain started (memory= and maxmem=).
> 
> xl create with 'memory = 700', no maxmem been set. I think it means maxmem = memory for this case.
> 
> >>> What were static-max and target at the point?
> 
>      /local/domain/3/memory/static-max = "716800"
>      /local/domain/3/memory/target = "716801"
> 
> >>> What did they change to when xl mem-max was issued? 
> 
> When I issue 'xl mem-max <domid> 700', static-max and target in xenstore will not change, but it will cause the command to fail.
> 
> Because: "libxl: error: libxl.c:4549:libxl_domain_setmaxmem: memory_static_max must be greater than or or equal to memory_dynamic_max"
> 
> >>> What did you expect them to change to instead?
> 
> I expect I can set the maxmem to the same value I initially set (700).

OK, thanks, got it. I think the use of xl mem-max is a bit of a
red-herring, the issue here is that static-max < target at start of day.

I suspect there is either a rounding error somewhere or because of
LIBXL_MAXMEM_CONSTANT being inconsistently applied to the two values
somewhere along the line.

We had been planning[0] to remove this early in the 4.5 cycle, but as
ever it never floated to the top of anyone's list. For 4.5 we should
probably look at applying this fudge more consistently.

Ian.

[0] http://bugs.xenproject.org/xen/bug/23