Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 28 Sep 2022 16:36:15 +0800
From:   Chih-En Lin <shiyn.lin@gmail.com>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Qi Zheng <zhengqi.arch@bytedance.com>,
        David Hildenbrand <david@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        William Kucharski <william.kucharski@oracle.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Peter Xu <peterx@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Tong Tiangen <tongtiangen@huawei.com>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        Li kunyu <kunyu@nfschina.com>, Nadav Amit <namit@vmware.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Minchan Kim <minchan@kernel.org>,
        Yang Shi <shy828301@gmail.com>, Song Liu <song@kernel.org>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Dinglan Peng <peng301@purdue.edu>,
        Pedro Fonseca <pfonseca@purdue.edu>,
        Jim Huang <jserv@ccns.ncku.edu.tw>,
        Huichun Feng <foxhoundsk.tw@gmail.com>
Subject: Re: [RFC PATCH v2 2/9] mm: pgtable: Add sysctl to enable COW PTE
Message-ID: <YzQHf8DOogqejrlP@strix-laptop>
References: <20220927162957.270460-1-shiyn.lin@gmail.com>
 <20220927162957.270460-3-shiyn.lin@gmail.com>
 <7db06e3d-5e00-2b8e-ea46-fbcdb82c4416@nvidia.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <7db06e3d-5e00-2b8e-ea46-fbcdb82c4416@nvidia.com>
Precedence: bulk

On Tue, Sep 27, 2022 at 02:22:27PM -0700, John Hubbard wrote:
> > +extern int sysctl_cow_pte_pid;
>
> So are setting a global value, to a single pid?? Only one pid at a time
> can be set up?
>
> I think that tells you already that there is a huge API problem here.
>
> As the other thread with Nadav said, this is not a sysctl. It wants to
> be a prctl(), at least the way things look so far.

I will change it to use the prctl().
Probably it will be under PR_SET_MM or create a new option.

> > +static void set_cow_pte_task(void)
> > +{
> > +   struct pid *pid;
> > +   struct task_struct *task;
> > +
> > +   pid = find_get_pid(sysctl_cow_pte_pid);
>
> This seems to be missing a corresponding call to put_pid().

Thanks.

> thanks,
>
> --
> John Hubbard
> NVIDIA
>

Best regards,
Chih-En Lin