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

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Message-ID: <20220521190859.GA1551274@strix-laptop>
Date:   Sun, 22 May 2022 03:08:59 +0800
From:   Chih-En Lin <shiyn.lin@...il.com>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        William Kucharski <william.kucharski@...cle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Arnd Bergmann <arnd@...db.de>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Colin Cross <ccross@...gle.com>,
        Feng Tang <feng.tang@...el.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Mike Rapoport <rppt@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Daniel Axtens <dja@...ens.net>,
        Jonathan Marek <jonathan@...ek.ca>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Peter Xu <peterx@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        linux-kernel@...r.kernel.org, Kaiyang Zhao <zhao776@...due.edu>,
        Huichun Feng <foxhoundsk.tw@...il.com>,
        Jim Huang <jserv.tw@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Subject: Re: [External] [RFC PATCH 0/6] Introduce Copy-On-Write to Page Table

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.