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

[Herbert Poetzl]

On Sun, Mar 11, 2007 at 06:04:28PM +0300, Pavel Emelianov wrote:
> 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'.

so what do we keep the context -> page reference
then at all?

> > 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.

must have missed some of them, please can you
point me to the relevant threads ...

TIA,
Herbert

> > 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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