Re: Strange finding about kernel samepage merging

On Mon, Feb 6, 2012 at 10:35 PM, Michael Roth [off-list ref] wrote:

My guess is you end up with 2 copies of each page on the guest: the copy in
the guest's page cache, and the copy in the buffer you allocated. From the
perspective of the host this all looks like anonymous memory, so ksm merges
the pages.

Yes, the result definitely shows that there two copies. But I don't
understand why there would be two copies. So whenever you allocate
memory in a guest OS, you will always create two copies of the same
memory?

An interesting thing is, if I replace the posix_memalign() function
with the malloc() function (See the original program, the commented
line.) there would be only one copy, i.e., no merging happens,
however, since I need to have some page-aligned memory, that's why I
use posix_memalign().

Regards
Jidong