Re: [RFC][PATCH 2/7] RSS controller core

[Pavel Emelianov]

Herbert Poetzl wrote:
> On Tue, Mar 06, 2007 at 02:00:36PM -0800, Andrew Morton wrote:
>> On Tue, 06 Mar 2007 17:55:29 +0300
>> Pavel Emelianov <xemul@xxxxx> wrote:
>>
>>> +struct rss_container {
>>> +	struct res_counter res;
>>> +	struct list_head page_list;
>>> +	struct container_subsys_state css;
>>> +};
>>> +
>>> +struct page_container {
>>> +	struct page *page;
>>> +	struct rss_container *cnt;
>>> +	struct list_head list;
>>> +};
>> ah. This looks good. I'll find a hunk of time to go through this work
>> and through Paul's patches. It'd be good to get both patchsets lined
>> up in -mm within a couple of weeks. But..
> 
> doesn't look so good for me, mainly becaus of the 
> additional per page data and per page processing
> 
> on 4GB memory, with 100 guests, 50% shared for each
> guest, this basically means ~1mio pages, 500k shared
> and 1500k x sizeof(page_container) entries, which
> roughly boils down to ~25MB of wasted memory ...
> 
> increase the amount of shared pages and it starts
> getting worse, but maybe I'm missing something here

You are. Each page has only one page_container associated
with it despite the number of containers it is shared
between.

>> We need to decide whether we want to do per-container memory
>> limitation via these data structures, or whether we do it via a
>> physical scan of some software zone, possibly based on Mel's patches.
> 
> why not do simple page accounting (as done currently
> in Linux) and use that for the limits, without
> keeping the reference from container to page?

As I've already answered in my previous letter simple
limiting w/o per-container reclamation and per-container
oom killer isn't a good memory management. It doesn't allow
to handle resource shortage gracefully.

This patchset provides more grace way to handle this, but
full memory management includes accounting of VMA-length
as well (returning ENOMEM from system call) but we've decided
to start with RSS.

> best,
> Herbert
> 
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