linux-kernel - Re: [PATCH V4 2/6] mm: mlock: Add new mlock, munlock, and munlockall system calls

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Date:	Wed, 22 Jul 2015 11:25:16 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Eric B Munson <emunson@...mai.com>, linux-mips@...ux-mips.org,
	linux-m68k@...r.kernel.org, linux-ia64@...r.kernel.org,
	linux-sh@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	sparclinux@...r.kernel.org, linux-arch@...r.kernel.org,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-am33-list@...hat.com,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Guenter Roeck <linux@...ck-us.net>,
	linux-xtensa@...ux-xtensa.org, linux-s390@...r.kernel.org,
	adi-buildroot-devel@...ts.sourceforge.net,
	linux-arm-kernel@...ts.infradead.org, linux-cris-kernel@...s.com,
	linux-parisc@...r.kernel.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH V4 2/6] mm: mlock: Add new mlock, munlock, and
 munlockall system calls

On Tue, 2015-07-21 at 13:44 -0700, Andrew Morton wrote:
> On Tue, 21 Jul 2015 15:59:37 -0400 Eric B Munson <emunson@...mai.com> wrote:
> 
> > With the refactored mlock code, introduce new system calls for mlock,
> > munlock, and munlockall.  The new calls will allow the user to specify
> > what lock states are being added or cleared.  mlock2 and munlock2 are
> > trivial at the moment, but a follow on patch will add a new mlock state
> > making them useful.
> > 
> > munlock2 addresses a limitation of the current implementation.  If a
> > user calls mlockall(MCL_CURRENT | MCL_FUTURE) and then later decides
> > that MCL_FUTURE should be removed, they would have to call munlockall()
> > followed by mlockall(MCL_CURRENT) which could potentially be very
> > expensive.  The new munlockall2 system call allows a user to simply
> > clear the MCL_FUTURE flag.
> 
> This is hard.  Maybe we shouldn't have wired up anything other than
> x86.  That's what we usually do with new syscalls.

Yeah I think so.

You haven't wired it up properly on powerpc, but I haven't mentioned it because
I'd rather we did it.

cheers


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