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In-Reply-To: <20190522154823.hu77qbjho5weado5@brauner.io>
From:   Daniel Colascione <dancol@google.com>
Date:   Wed, 22 May 2019 08:57:47 -0700
Message-ID: <CAKOZuev97fTvmXhEkjb7_RfDvjki4UoPw+QnVOsSAg0RB8RyMQ@mail.gmail.com>
Subject: Re: [RFC 0/7] introduce memory hinting API for external process
To:     Christian Brauner <christian@brauner.io>
Cc:     Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tim Murray <timmurray@google.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        Sonny Rao <sonnyrao@google.com>,
        Brian Geffon <bgeffon@google.com>, Jann Horn <jannh@google.com>
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On Wed, May 22, 2019 at 8:48 AM Christian Brauner <christian@brauner.io> wrote:
>
> On Wed, May 22, 2019 at 08:17:23AM -0700, Daniel Colascione wrote:
> > On Wed, May 22, 2019 at 7:52 AM Christian Brauner <christian@brauner.io> wrote:
> > > I'm not going to go into yet another long argument. I prefer pidfd_*.
> >
> > Ok. We're each allowed our opinion.
> >
> > > It's tied to the api, transparent for userspace, and disambiguates it
> > > from process_vm_{read,write}v that both take a pid_t.
> >
> > Speaking of process_vm_readv and process_vm_writev: both have a
> > currently-unused flags argument. Both should grow a flag that tells
> > them to interpret the pid argument as a pidfd. Or do you support
> > adding pidfd_vm_readv and pidfd_vm_writev system calls? If not, why
> > should process_madvise be called pidfd_madvise while process_vm_readv
> > isn't called pidfd_vm_readv?
>
> Actually, you should then do the same with process_madvise() and give it
> a flag for that too if that's not too crazy.

I don't know what you mean. My gut feeling is that for the sake of
consistency, process_madvise, process_vm_readv, and process_vm_writev
should all accept a first argument interpreted as either a numeric PID
or a pidfd depending on a flag --- ideally the same flag. Is that what
you have in mind?