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Subject: Re: [PATCH v7 5/7] mm: support both pid and pidfd for process_madvise
To:     Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
        linux-api@vger.kernel.org, oleksandr@redhat.com,
        Suren Baghdasaryan <surenb@google.com>,
        Tim Murray <timmurray@google.com>,
        Daniel Colascione <dancol@google.com>,
        Sandeep Patil <sspatil@google.com>,
        Sonny Rao <sonnyrao@google.com>,
        Brian Geffon <bgeffon@google.com>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shakeel Butt <shakeelb@google.com>,
        John Dias <joaodias@google.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Jann Horn <jannh@google.com>,
        alexander.h.duyck@linux.intel.com, sj38.park@gmail.com,
        Christian Brauner <christian@brauner.io>,
        Kirill Tkhai <ktkhai@virtuozzo.com>
References: <20200302193630.68771-1-minchan@kernel.org>
 <20200302193630.68771-6-minchan@kernel.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <14089609-5fb1-b082-716f-c2e129d27c48@suse.cz>
Date:   Fri, 6 Mar 2020 12:14:19 +0100
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On 3/2/20 8:36 PM, Minchan Kim wrote:
> 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(int which, pid_t pid, void *addr,
> 		size_t length, int advise, unsigned long flag);

This is again halfway between kernel and userspace description, so if we stick
to userspace then it's:

 	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.
> 
> [1]  https://lore.kernel.org/linux-mm/9d849087-3359-c4ab-fbec-859e8186c509@virtuozzo.com/
> 
> Cc: Christian Brauner <christian@brauner.io>
> Reviewed-by: Suren Baghdasaryan <surenb@google.com>
> Suggested-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>