linux-kernel - Re: [RFC PATCH v2 1/9] mm: Add new mm flags for Copy-On-Write PTE table

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Date:   Tue, 27 Sep 2022 17:23:58 +0000
From:   Nadav Amit <namit@...are.com>
To:     Chih-En Lin <shiyn.lin@...il.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        William Kucharski <william.kucharski@...cle.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Peter Xu <peterx@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Tong Tiangen <tongtiangen@...wei.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Li kunyu <kunyu@...china.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Minchan Kim <minchan@...nel.org>,
        Yang Shi <shy828301@...il.com>, Song Liu <song@...nel.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Dinglan Peng <peng301@...due.edu>,
        Pedro Fonseca <pfonseca@...due.edu>,
        Jim Huang <jserv@...s.ncku.edu.tw>,
        Huichun Feng <foxhoundsk.tw@...il.com>
Subject: Re: [RFC PATCH v2 1/9] mm: Add new mm flags for Copy-On-Write PTE
 table

On Sep 27, 2022, at 9:29 AM, Chih-En Lin <shiyn.lin@...il.com> wrote:

> Add MMF_COW_PTE{, _READY} flags to prepare the subsequent
> implementation of Copy-On-Write for the page table.
> 
> Signed-off-by: Chih-En Lin <shiyn.lin@...il.com>
> ---
> include/linux/sched/coredump.h | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
> index 4d0a5be28b70f..f03ff69c90c8c 100644
> --- a/include/linux/sched/coredump.h
> +++ b/include/linux/sched/coredump.h
> @@ -84,7 +84,13 @@ static inline int get_dumpable(struct mm_struct *mm)
> #define MMF_HAS_PINNED		28	/* FOLL_PIN has run, never cleared */
> #define MMF_DISABLE_THP_MASK	(1 << MMF_DISABLE_THP)
> 
> +#define MMF_COW_PTE_READY	29
> +#define MMF_COW_PTE_READY_MASK	(1 << MMF_COW_PTE_READY)
> +
> +#define MMF_COW_PTE		30
> +#define MMF_COW_PTE_MASK	(1 << MMF_COW_PTE)

I am not sure how much sense it makes to put it in a separate patch, and it
is rather hard to understand the new flags without proper documentation and
comments.