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

[Pavel Emelianov]

Herbert Poetzl wrote:
> On Sun, Mar 11, 2007 at 12:08:16PM +0300, Pavel Emelianov wrote:
>> 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 at sw.ru> 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.
> 
> per container OOM killer does not require any container
> page reference, you know _what_ tasks belong to the 
> container, and you know their _badness_ from the normal
> OOM calculations, so doing them for a container is really
> straight forward without having any page 'tagging'

That's true. If you look at the patches you'll
find out that no code in oom killer uses page 'tag'.

> for the reclamation part, please elaborate how that will
> differ in a (shared memory) guest from what the kernel
> currently does ...

This is all described in the code and in the
discussions we had before.

> TIA,
> Herbert
> 
>> 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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