[Devel] Re: [RFC][PATCH 3/7] Data structures changes for RSS accounting

[Pavel Emelianov]

Dave Hansen wrote:
> On Mon, 2007-03-12 at 19:16 +0300, Kirill Korotaev wrote:
>> now VE2 maps the same page. You can't determine whether this page is mapped
>> to this container or another one w/o page->container pointer. 
> 
> Hi Kirill,
> 
> I thought we can always get from the page to the VMA.  rmap provides
> this to us via page->mapping and the 'struct address_space' or anon_vma.
> Do we agree on that?

Not completely. When page is unmapped from the *very last*
user its *first* toucher may already be dead. So we'll never
find out who it was.

> We can also get from the vma to the mm very easily, via vma->vm_mm,
> right?
> 
> We can also get from a task to the container quite easily.  
> 
> So, the only question becomes whether there is a 1:1 relationship
> between mm_structs and containers.  Does each mm_struct belong to one

No. The question is "how to get a container that touched the
page first" which is the same as "how to find mm_struct which
touched the page first". Obviously there's no answer on this
question unless we hold some direct page->container reference.
This may be a hash, a direct on-page pointer, or mirrored
array of pointers.

> and only one container?  Basically, can a threaded process have
> different threads in different containers?
> 
> It seems that we could bridge the gap pretty easily by either assigning
> each mm_struct to a container directly, or putting some kind of
> task-to-mm lookup.  Perhaps just a list like
> mm->tasks_using_this_mm_list.

This could work for reclamation: we scan through all the
mm_struct-s within the container and shrink its' pages, but
we can't make LRU this way.

> Not rocket science, right?
> 
> -- Dave
> 
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