linux-kernel - Re: [PATCH v8 3/4] mm/madvise: introduce process_madvise() syscall: an external memory hinting API

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Date:   Sat, 29 Aug 2020 08:02:30 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        linux-mm <linux-mm@...ck.org>,
        Linux API <linux-api@...r.kernel.org>,
        Oleksandr Natalenko <oleksandr@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...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,
        SeongJae Park <sj38.park@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Arjun Roy <arjunroy@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christian Brauner <christian@...uner.io>,
        Daniel Colascione <dancol@...gle.com>,
        Jens Axboe <axboe@...nel.dk>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        SeongJae Park <sjpark@...zon.de>,
        linux-man <linux-man@...r.kernel.org>
Subject: Re: [PATCH v8 3/4] mm/madvise: introduce process_madvise() syscall:
 an external memory hinting API

On Fri, Aug 28, 2020 at 07:40:08PM +0200, Arnd Bergmann wrote:
> Every syscall that passes an iovec seems to do this. If we make import_iovec()
> handle both cases directly, this syscall and a number of others can
> be simplified, and you avoid the x32 entry point I mentioned above

FYI, I do have a series that does this (even tested) and kills tons of
compat syscalls by that.  But by doing that I found the problem that
compat syscalls issued by io_uring don't trigger in_compat_syscall().
I need to go back to fixing the io_uring vs in_compat_syscall() issue
(probably for 5.9) and then submit the whole thing.