linux-kernel - Re: [PATCH] mm/mincore: allow for making sys

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Message-ID: <20190106001138.GW6310@bombadil.infradead.org>
Date:   Sat, 5 Jan 2019 16:11:38 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jann Horn <jannh@...gle.com>, Jiri Kosina <jikos@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>, Linux-MM <linux-mm@...ck.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

On Sat, Jan 05, 2019 at 03:39:10PM -0800, Linus Torvalds wrote:
> On Sat, Jan 5, 2019 at 3:16 PM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > It goes back to forever, it looks like. I can't find a reason.
> 
> mincore() was originally added in 2.3.52pre3, it looks like. Around
> 2000 or so. But sadly before the BK history.
> 
> And that comment about
> 
>   "Later we can get more picky about what "in core" means precisely."
> 
> that still exists above mincore_page() goes back to the original patch.

FreeBSD claims to have a manpage from SunOS 4.1.3 with mincore (!)

https://www.freebsd.org/cgi/man.cgi?query=mincore&apropos=0&sektion=0&manpath=SunOS+4.1.3&arch=default&format=html

DESCRIPTION
       mincore()  returns  the primary memory residency	status of pages	in the
       address space covered by	mappings in the	range [addr, addr + len).  The
       status is returned as a char-per-page in	the character array referenced
       by *vec (which the system assumes to be large enough to	encompass  all
       the  pages  in  the  address range).  The least significant bit of each
       character is set	to 1 to	indicate that the referenced page is  in  pri-
       mary  memory, 0 if it is	not.  The settings of other bits in each char-
       acter is	undefined and may contain other	information in the future.