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SubjectRe: [PATCH 0/3] ksm: fix incorrect count of merged pages when enabling use_zero_pages
On 29.09.22 04:52, xu.xin.sc@gmail.com wrote:
> From: xu xin <xu.xin16@zte.com.cn>
>
> Before enabling use_zero_pages by setting /sys/kernel/mm/ksm/
> use_zero_pages to 1, pages_sharing of KSM is basically accurate. But
> after enabling use_zero_pages, all empty pages that are merged with
> kernel zero page are not counted in pages_sharing or pages_shared.
> That is because the rmap_items of these ksm zero pages are not
> appended to The Stable Tree of KSM.
>
> 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?

--
Thanks,

David / dhildenb

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