Re: [Xen-devel] [PATCH v3 3/3] tools: introduce parameter max_wp_ram_ranges.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.02.16 at 14:07, <Paul.Durrant@xxxxxxxxxx> wrote:
>>  -----Original Message-----
> [snip]
>> >> >> I'm getting the impression that we're moving in circles. A blanket
>> >> >> limit above the 256 one for all domains is _not_ going to be
>> >> >> acceptable; going to 8k will still need host admin consent. With
>> >> >> your rangeset performance improvement patch, each range is
>> >> >> going to be tracked by a 40 byte structure (up from 32), which
>> >> >> already means an overhead increase for all the other ranges. 8k
>> >> >> of wp ranges implies an overhead beyond 448k (including the
>> >> >> xmalloc() overhead), which is not _that_ much, but also not
>> >> >> negligible.
>> >> >>
>> >> >
>> >> > ... which means we are still going to need a toolstack parameter to set
>> the
>> >> > limit. We already have a parameter for VRAM size so is having a
>> parameter
>> >> for
>> >> > max. GTT shadow ranges such a bad thing?
>> >>
>> >> It's workable, but not nice (see also Ian's earlier response).
>> >>
>> >> > Is the fact that the memory comes
>> >> > from xenheap rather than domheap the real problem?
>> >>
>> >> Not the primary one, since except on huge memory machines
>> >> both heaps are identical. To me the primary one is the quite
>> >> more significant resource consumption in the first place (I'm not
>> >> going to repeat what I've written in already way too many
>> >> replies before).
>> >
>> > Ok. Well the only way round tracking specific ranges for emulation (and
>> > consequently suffering the overhead) is tracking by type. For XenGT I
>> guess
>> > it would be possible to live with a situation where a single ioreq server 
>> > can
>> > register all wp mem emulations for a given VM. I can't say I particularly
>> > like that way of doing things but if it's the only way forward then I guess
>> > we may have to live with it.
>> 
>> Well, subject to Ian not objecting (still awaiting some follow-up by
>> him), I didn't mean to say doing it the proposed way is a no-go.
>> All that I really insist on is that this larger resource consumption
>> won't go without some form of host admin consent.
> 
> Would you be ok with purely host admin consent e.g. just setting the limit 
> via boot command line?

I wouldn't be happy with that (and I've said so before), since it
would allow all VM this extra resource consumption.

Jan


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