Reply:[PATCH 0/3] ksm: fix incorrect count of merged pages when enabling use_zero_pages

[xu xin <xu.xin.sc@gmail.com>]

>> We need to add the count of empty pages to let users know how many empty
>> pages are merged with kernel zero page(s).
>> 
>> Please see the subsequent patches for details.

> Just raising the topic here because it's related to the KSM usage of the 
> shared zero-page:

> MADV_UNMERGEABLE and other ways to trigger unsharing will *not* unshare 
> the shared zeropage as placed by KSM (which is against the 
> MADV_UNMERGEABLE documentation at least). It will only unshare actual 
> KSM pages. We might not want want to blindly unshare all shared 
> zeropages in applicable VMAs ... using a dedicated shared zero (KSM) 
> page -- instead of the generic zero page --  might be one way to handle 
> this cleaner.

> Would that also fix some of the issues you describe above?

Glad to see your reply. I think it depends.

The way you said solves the issue you post, but maybe not help to solve the issue
I post.

The key lies in whether appending zeropage's rmap_items to stable tree. If
appending their rmap_items to the stable tree, the issue I pointed can be fixed but
that will degrade the performance of use_zero_pages.  If not appending their rmap_items
to the stable tree, we have to choose this patches set (but I found some bugs now, later
I will send v2 to fix it).