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From: Daniel Jordan <daniel.m.jordan@oracle.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	akpm@linux-foundation.org, dave@stgolabs.net, jack@suse.cz,
	cl@linux.com, linux-mm@kvack.org, kvm@vger.kernel.org,
	kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org,
	paulus@ozlabs.org, benh@kernel.crashing.org, mpe@ellerman.id.au,
	hao.wu@intel.com, atull@kernel.org, mdf@kernel.org,
	aik@ozlabs.ru, peterz@infradead.org
Subject: Re: [PATCH 1/5] vfio/type1: use pinned_vm instead of locked_vm to account pinned pages
Date: Tue, 12 Feb 2019 19:26:50 -0500	[thread overview]
Message-ID: <20190213002650.kav7xc4r2xs5f3ef@ca-dmjordan1.us.oracle.com> (raw)
In-Reply-To: <20190212114110.17bc8a14@w520.home>

On Tue, Feb 12, 2019 at 11:41:10AM -0700, Alex Williamson wrote:
> Daniel Jordan <daniel.m.jordan@oracle.com> wrote:
> > On Mon, Feb 11, 2019 at 03:56:20PM -0700, Jason Gunthorpe wrote:
> > > I haven't looked at this super closely, but how does this stuff work?
> > > 
> > > do_mlock doesn't touch pinned_vm, and this doesn't touch locked_vm...
> > > 
> > > Shouldn't all this be 'if (locked_vm + pinned_vm < RLIMIT_MEMLOCK)' ?
> > >
> > > Otherwise MEMLOCK is really doubled..  
> > 
> > So this has been a problem for some time, but it's not as easy as adding them
> > together, see [1][2] for a start.
> > 
> > The locked_vm/pinned_vm issue definitely needs fixing, but all this series is
> > trying to do is account to the right counter.

Thanks for taking a look, Alex.

> This still makes me nervous because we have userspace dependencies on
> setting process locked memory.

Could you please expand on this?  Trying to get more context.

> There's a user visible difference if we
> account for them in the same bucket vs separate.  Perhaps we're
> counting in the wrong bucket now, but if we "fix" that and userspace
> adapts, how do we ever go back to accounting both mlocked and pinned
> memory combined against rlimit?  Thanks,

PeterZ posted an RFC that addresses this point[1].  It kept pinned_vm and
locked_vm accounting separate, but allowed the two to be added safely to be
compared against RLIMIT_MEMLOCK.

Anyway, until some solution is agreed on, are there objections to converting
locked_vm to an atomic, to avoid user-visible changes, instead of switching
locked_vm users to pinned_vm?

Daniel

[1] http://lkml.kernel.org/r/20130524140114.GK23650@twins.programming.kicks-ass.net


  reply	other threads:[~2019-02-13  0:27 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-11 22:44 [PATCH 0/5] use pinned_vm instead of locked_vm to account pinned pages Daniel Jordan
2019-02-11 22:44 ` [PATCH 1/5] vfio/type1: " Daniel Jordan
2019-02-11 22:56   ` Jason Gunthorpe
2019-02-11 23:11     ` Daniel Jordan
2019-02-12 18:41       ` Alex Williamson
2019-02-13  0:26         ` Daniel Jordan [this message]
2019-02-13 20:03           ` Alex Williamson
2019-02-13 23:07             ` Jason Gunthorpe
2019-02-14  1:46             ` Daniel Jordan
2019-02-11 22:44 ` [PATCH 2/5] vfio/spapr_tce: " Daniel Jordan
2019-02-12  6:56   ` Alexey Kardashevskiy
2019-02-12 16:50     ` Christopher Lameter
2019-02-12 17:18       ` Daniel Jordan
2019-02-13  0:37         ` Alexey Kardashevskiy
2019-02-12 18:56     ` Alex Williamson
2019-02-13  0:34       ` Alexey Kardashevskiy
2019-02-11 22:44 ` [PATCH 3/5] fpga/dlf/afu: " Daniel Jordan
2019-02-11 22:44 ` [PATCH 4/5] powerpc/mmu: " Daniel Jordan
2019-02-13  1:14   ` kbuild test robot
2019-02-11 22:44 ` [PATCH 5/5] kvm/book3s: " Daniel Jordan
2019-02-13  1:43   ` kbuild test robot
2019-02-11 22:54 ` [PATCH 0/5] " Jason Gunthorpe
2019-02-11 23:15   ` Daniel Jordan
2019-02-14  1:53   ` Ira Weiny
2019-02-14  6:00     ` Jason Gunthorpe
2019-02-14 19:33       ` Ira Weiny
2019-02-14 20:12         ` Jason Gunthorpe
2019-02-14 21:46           ` Ira Weiny
2019-02-14 22:16             ` Jason Gunthorpe
2019-02-15 15:26               ` Christopher Lameter

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