linux-kernel - Re: [PATCH 2/4] mm: introduce external memory hinting API

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Date:   Mon, 13 Jan 2020 10:44:08 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Kirill Tkhai <ktkhai@...tuozzo.com>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
        oleksandr@...hat.com, Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Dias <joaodias@...gle.com>
Subject: Re: [PATCH 2/4] mm: introduce external memory hinting API

On Mon, Jan 13, 2020 at 11:42:57AM +0100, Christian Brauner wrote:
> On Mon, Jan 13, 2020 at 11:47:11AM +0300, Kirill Tkhai wrote:

< snip >

> > > +SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start,
> > > +		size_t, len_in, int, behavior, unsigned long, flags)
> > 
> > I don't like the interface. The fact we have pidfd does not mean,
> > we have to use it for new syscalls always. A user may want to set
> > madvise for specific pid from console and pass pid as argument.
> > pidfd would be an overkill in this case.
> > We usually call "kill -9 pid" from console. Why shouldn't process_madvise()
> > allow this?
> > 
> > I suggent to extend first argument to work with both pid and pidfd.
> > Look at what we have for waitid(idtype, id_t id, ...) for example:
> > 
> >        idtype == P_PID
> >               Wait for the child whose process ID matches id.
> > 
> >        idtype == P_PIDFD (since Linux 5.4)
> >               Wait for the child referred to by the PID file descriptor specified in id.  (See pidfd_open(2) for  further  information  on
> >               PID file descriptors.)
> > 
> > We may use @flags argument for this.
> 
> Sorry for chiming in just a comment. Overall, I don't particularly care
> how or if you integrate pidfd here. One thing I would like to point out
> is that we're working on a patch to place new features under pidfd
> specific flags. This e.g. means a pidfd would be only be able to be used
> for madvise operations (or getfd operations) if it was created with that
> specific flag set making it easier to share them with other processes.
> So if you integrate them here I would be quite thankful if you target
> the patchset for the v5.7 merge window, not for v5.6.

Hi Christian,
Sorry but I couldn't understand your point.
Could you clarify what you meant?

Thanks.