linux-kernel - Re: [PATCH 1/6] mm: change locked_vm's type from unsigned long to atomic64

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Date:   Wed, 3 Apr 2019 12:07:02 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Alan Tull <atull@...nel.org>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Lameter <cl@...ux.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Moritz Fischer <mdf@...nel.org>,
        Paul Mackerras <paulus@...abs.org>, Wu Hao <hao.wu@...el.com>,
        linux-mm@...ck.org, kvm@...r.kernel.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-fpga@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] mm: change locked_vm's type from unsigned long to
 atomic64_t

On Tue, Apr 02, 2019 at 04:43:57PM -0700, Davidlohr Bueso wrote:
> On Tue, 02 Apr 2019, Andrew Morton wrote:
> 
> > Also, we didn't remove any down_write(mmap_sem)s from core code so I'm
> > thinking that the benefit of removing a few mmap_sem-takings from a few
> > obscure drivers (sorry ;)) is pretty small.
> 
> afaik porting the remaining incorrect users of locked_vm to pinned_vm was
> the next step before this one, which made converting locked_vm to atomic
> hardly worth it. Daniel?
 
Right, as you know I tried those incorrect users first, but there were concerns
about user-visible changes regarding RLIMIT_MEMLOCK and pinned_vm/locked_vm
without the accounting problem between all three being solved.

To my knowledge no one has a solution for that, so in the meantime I'm taking
the incremental step of getting rid of mmap_sem for locked_vm users.  The
locked_vm -> pinned_vm conversion can happen later.