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

[Claudio Imbrenda]

On Thu, 29 Sep 2022 02:52:06 +0000
xu.xin.sc@xxxxxxxxx wrote:

> From: xu xin <xu.xin16@xxxxxxxxxx>
> 
> 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's because those pages are not shared between different processes.

> 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).

why?

do you need to know how many untouched zero pages a process has?

does it make a difference if the zero page is really untouched or if it
was touched in the past but it is now zero?

> 
> Please see the subsequent patches for details.
> 
> 
> 
> 
> *** BLURB HERE ***
> 
> xu xin (3):
>   ksm: abstract the function try_to_get_old_rmap_item
>   ksm: add the accounting of zero pages merged by use_zero_pages
>   ksm: add zero_pages_merged in Documentation
> 
>  Documentation/admin-guide/mm/ksm.rst |  10 ++-
>  mm/ksm.c                             | 122 +++++++++++++++++++++------
>  2 files changed, 106 insertions(+), 26 deletions(-)
>