Re: Strange finding about kernel samepage merging

[Jidong Xiao <jidong.xiao@gmail.com>]

On Mon, Feb 6, 2012 at 10:35 PM, Michael Roth <mdroth@linux.vnet.ibm.com> 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

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