linux-kernel - Re: [RFC PATCH 2/6] mm: clone3: Add CLONE_COW

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Message-ID: <20220521035006.GB1506735@strix-laptop>
Date:   Sat, 21 May 2022 11:50:06 +0800
From:   Chih-En Lin <shiyn.lin@...il.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        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>,
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        Andy Lutomirski <luto@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        David Hildenbrand <david@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kaiyang Zhao <zhao776@...due.edu>,
        Huichun Feng <foxhoundsk.tw@...il.com>,
        Jim Huang <jserv.tw@...il.com>
Subject: Re: [RFC PATCH 2/6] mm: clone3: Add CLONE_COW_PGTABLE flag

On Fri, May 20, 2022 at 02:13:25PM +0000, Christophe Leroy wrote:
> 
> 
> Le 19/05/2022 à 20:31, Chih-En Lin a écrit :
> > Add CLONE_COW_PGTABLE flag to support clone3() system call to enable the
> > Copy-On-Write (COW) mechanism on the page table.
> 
> Is that really something we want the user to decide ? Isn't it an 
> internal stuff that should be transparent for users ?
> 
> As far as I know, there is no way today to decide whether you want COW 
> or not for main memory. Why should there be a choice for the COW of page 
> tables ?

Agree.
It should not expose to the user.
COW of page table should become the configuration.
Or, if the change is fine, it can even be the default setting.

Thanks.

---

Sorry I did not group reply the first time.