Re: [Xen-devel] how mem-set / balloon changes totalram_pages

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> I find that after I use xm mem-set to change the current memory
> allocation of a dom, the MemTotal in /proc/meminfo will give the
> current allocation.
>
> In my understanding, the balloon driver simply alloc / free pages, so
> the MemTotal should not be changed. Only the free memory will be
> affected.
>
> In normal linux, the value of MemTotal comes from "totalram_pages"
> defined in arch/i386/mm/init.c
>
> I tried to located the code in Xen, which changes the variable, but I
> didn't find such code.

This variable is updated by the balloon driver in XenLinux 
(drivers/xen/balloon/balloon.c).  totalram_pages is declared as an extern 
there - when the balloon changes size, totalram_pages is updated accordingly.

> I tried to locate the implementation of  HYPERCALL_memory_op, but I
> can only traced to
> "call hypercall_page + STR(...)"
>
> Can someone tell me where I can find the actual implementation of
> those hypercalls?

Well, the code you found implements the call into Xen.  It gets handled 
eventually by do_memory_op in xen/common/memory.c under the Xen repository.  
This implements the memory ops and then returns to the guest (and thence to 
the balloon driver).

Hope that helps,

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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