linux-kernel - Re: [RFC 0/7] introduce memory hinting API for external process

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Message-ID: <20190522160108.l5i7t4lkfy3tyx3z@brauner.io>
Date:   Wed, 22 May 2019 18:01:09 +0200
From:   Christian Brauner <christian@...uner.io>
To:     Daniel Colascione <dancol@...gle.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tim Murray <timmurray@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>, Jann Horn <jannh@...gle.com>
Subject: Re: [RFC 0/7] introduce memory hinting API for external process

On Wed, May 22, 2019 at 08:57:47AM -0700, Daniel Colascione wrote:
> On Wed, May 22, 2019 at 8:48 AM Christian Brauner <christian@...uner.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@...uner.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?

Yes. For the sake of consistency they should probably all default to
interpret as pid and if say PROCESS_{VM_}PIDFD is passed as flag
interpret as pidfd.