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

[Herbert Poetzl]

On Sun, Mar 11, 2007 at 04:51:11AM -0800, Andrew Morton wrote:
> > On Sun, 11 Mar 2007 15:26:41 +0300 Kirill Korotaev <dev at sw.ru> wrote:
> > 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..
> > >
> > > 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.
> > i.e. a separate memzone for each container?
> 
> Yep. Straightforward machine partitioning. An attractive thing is that
> it 100% reuses existing page reclaim, unaltered.
> 
> > imho memzone approach is inconvinient for pages sharing and shares
> > accounting. it also makes memory management more strict, forbids
> > overcommiting per-container etc.
> 
> umm, who said they were requirements?

well, I guess all existing OS-Level virtualizations
(Linux-VServer, OpenVZ, and FreeVPS) have stated more
than one time that _sharing_ of resources is a central
element, and one especially important resource to share
is memory (RAM) ...

if your aim is full partitioning, we do not need to
bother with OS-Level isolation, we can simply use
Paravirtualization and be done ...

> > Maybe you have some ideas how we can decide on this?
> 
> We need to work out what the requirements are before we can 
> settle on an implementation.

Linux-VServer (and probably OpenVZ):

 - shared mappings of 'shared' files (binaries 
   and libraries) to allow for reduced memory
   footprint when N identical guests are running

 - virtual 'physical' limit should not cause
   swap out when there are still pages left on
   the host system (but pages of over limit guests
   can be preferred for swapping)

 - accounting and limits have to be consistent
   and should roughly represent the actual used
   memory/swap (modulo optimizations, I can go
   into detail here, if necessary)

 - OOM handling on a per guest basis, i.e. some
   out of memory condition in guest A must not
   affect guest B

HTC,
Herbert

> Sigh.  Who is running this show?   Anyone?
> 
> You can actually do a form of overcommittment by allowing multiple
> containers to share one or more of the zones. Whether that is
> sufficient or suitable I don't know. That depends on the requirements,
> and we haven't even discussed those, let alone agreed to them.
> 
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