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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 5 Jan 2019 15:16:32 -0800
Message-ID: <CAHk-=wg5Kk+r36=jcGBaLUj+gjopjgiW5eyvkdMqvn0jFkD_iQ@mail.gmail.com>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged
To:     Jann Horn <jannh@google.com>
Cc:     Jiri Kosina <jikos@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Michal Hocko <mhocko@suse.com>, Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>
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On Sat, Jan 5, 2019 at 3:05 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> That would be nicer than my patch, simply because removing code is
> always nice. And arguably it's a better semantic anyway.

Yeah, I wonder why we did that thing where mincore() walks the page
tables, but if they are empty it looks in the page cache.

[... goes and looks in history ..]

It goes back to forever, it looks like. I can't find a reason.

Anyway, a removal patch would look something like the attached, I
think. That makes mincore() actually say how many pages are in _this_
mapping, not how many pages could be paged in without doing IO.

Hmm. Maybe we should try this first. Simplicity is always good.

Again, obviously untested.

                   Linus

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