Re: [External] [RFC PATCH 0/6] Introduce Copy-On-Write to Page Table

Chih-En Lin
2022-05-21T19:09:11Z

On Sat, May 21, 2022 at 04:59:19PM +0800, Qi Zheng wrote:
> Hi,
>
> To reduce the empty user PTE tables, I also introduced a reference
> count (pte_ref) for user PTE tables in my patch[1][2], It is used
> to track the usage of each user PTE tables.
>
> The following people will hold a pte_ref:
> - The !pte_none() entry, such as regular page table entry that map
> physical pages, or swap entry, or migrate entry, etc.
> - Visitor to the PTE page table entries, such as page table walker.
>
> With COW PTE, a new holder (the process using the COW PTE) is added.
>
> It's funny, it leads me to see more meaning of pte_ref.
>
> Thanks,
> Qi
>
> [1] [RFC PATCH 00/18] Try to free user PTE page table pages
> link: https://lore.kernel.org/lkml/20220429133552.33768-1-zhengqi.arch@bytedance.com/
> (percpu_ref version)
>
> [2] [PATCH v3 00/15] Free user PTE page table pages
> link: https://lore.kernel.org/lkml/20211110105428.32458-1-zhengqi.arch@bytedance.com/
> (atomic count version)
>
> --
> Thanks,
> Qi

Hi,

I saw your patch a few months ago.
Actually, my school's independent study is tracing the page table. And
one of the topics is your patch. It is really helpful from your pte_ref.
It's great to see you have more ideas for your pte_ref.

Thanks.