linux-kernel - Re: [PATCH v7 5/7] mm: support both pid and pidfd for process

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Date:   Fri, 8 May 2020 16:04:15 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        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>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Dias <joaodias@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Jann Horn <jannh@...gle.com>,
        alexander.h.duyck@...ux.intel.com, sj38.park@...il.com,
        Christian Brauner <christian@...uner.io>,
        Kirill Tkhai <ktkhai@...tuozzo.com>
Subject: Re: [PATCH v7 5/7] mm: support both pid and pidfd for
 process_madvise

On Fri, 8 May 2020 11:36:53 -0700 Minchan Kim <minchan@...nel.org> wrote:

> 
> ...
>
> Per Vlastimil's request, I changed "which and advise" with "idtype and
> advice" in function prototype of description.
> Could you replace the part in the description? Code is never changed.
> 

Done, but...

>
> ...
>
> There is a demand[1] to support pid as well pidfd for process_madvise to
> reduce unnecessary syscall to get pidfd if the user has control of the
> target process(ie, they could guarantee the process is not gone or pid is
> not reused).
> 
> This patch aims for supporting both options like waitid(2).  So, the
> syscall is currently,
> 
>         int process_madvise(idtype_t idtype, id_t id, void *addr,
>                 size_t length, int advice, unsigned long flags);
> 
> @which is actually idtype_t for userspace libray and currently, it
> supports P_PID and P_PIDFD.

What does "@which is actually idtype_t for userspace libray" mean?  Can
you clarify and expand?

Also, does this userspace library exist?  If so, where is it?

>
> ...
>