[Lguest] Doubt about memory translation

[Gaurav Kukreja]

Hi,

Is there any such mechanism to allocate pages, and map in the process
virtual space, where we need it?

Such a mechanism would prove useful, in ballooning, where a page ballooned
by a guest can be freed by launcher. When this page is required to be
deflated, it can be allocated at the same address in the virtual space of
the launcher, so as to be able to use the simple address translation, that
lguest is currently using.

It could be much better, if there was a mechanism, to free a page, but still
keep its mapping in the process virtual space, and be able to map pages to
the same address later.

I have managed to balloon, by changing the address translation scheme, but
this adds quite an overhead.

I free pages in a chunk of size which is a power of 2. These addresses are
kept in increasing order in a link list, and the pages are freed. When a
translation is required, number of chunks before the required address are
counted, in this linklist, and accordingly difference is accounted in the
virtual address of the launcher.

Another list is kept for deflated pages. These deflated pages are allocated
at a new address in launcher virtual memory. These launcher virtual
addresses are stored alongwith the guest pfn they should map to in the
deflate_list. When a page from deflated space is referred, the particular
chunk that the page belong to is located in the deflated list, and address
is translated to the new address it is mapped in.

I am not being able to come up with a better solution. Please suggest some
better solutions for the same.

Regards,

---

Gaurav Kukreja (India)
+91 997 030 1257
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