From: Ira Weiny <ira.weiny@intel.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: dave@stgolabs.net, jack@suse.cz, kvm@vger.kernel.org,
atull@kernel.org, aik@ozlabs.ru, linux-fpga@vger.kernel.org,
linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org,
Daniel Jordan <daniel.m.jordan@oracle.com>,
linux-mm@kvack.org, alex.williamson@redhat.com, mdf@kernel.org,
akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org,
cl@linux.com, hao.wu@intel.com
Subject: Re: [PATCH 0/5] use pinned_vm instead of locked_vm to account pinned pages
Date: Thu, 14 Feb 2019 11:33:53 -0800 [thread overview]
Message-ID: <20190214193352.GA7512@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20190214060006.GE24692@ziepe.ca>
On Wed, Feb 13, 2019 at 11:00:06PM -0700, Jason Gunthorpe wrote:
> On Wed, Feb 13, 2019 at 05:53:14PM -0800, Ira Weiny wrote:
> > On Mon, Feb 11, 2019 at 03:54:47PM -0700, Jason Gunthorpe wrote:
> > > On Mon, Feb 11, 2019 at 05:44:32PM -0500, Daniel Jordan wrote:
> > >
> > > > All five of these places, and probably some of Davidlohr's conversions,
> > > > probably want to be collapsed into a common helper in the core mm for
> > > > accounting pinned pages. I tried, and there are several details that
> > > > likely need discussion, so this can be done as a follow-on.
> > >
> > > I've wondered the same..
> >
> > I'm really thinking this would be a nice way to ensure it gets cleaned up and
> > does not happen again.
> >
> > Also, by moving it to the core we could better manage any user visible changes.
> >
> > From a high level, pinned is a subset of locked so it seems like we need a 2
> > sets of helpers.
> >
> > try_increment_locked_vm(...)
> > decrement_locked_vm(...)
> >
> > try_increment_pinned_vm(...)
> > decrement_pinned_vm(...)
> >
> > Where try_increment_pinned_vm() also increments locked_vm... Of course this
> > may end up reverting the improvement of Davidlohr Bueso's atomic work... :-(
> >
> > Furthermore it would seem better (although I don't know if at all possible) if
> > this were accounted for in core calls which tracked them based on how the pages
> > are being used so that drivers can't call try_increment_locked_vm() and then
> > pin the pages... Thus getting the account wrong vs what actually happened.
> >
> > And then in the end we can go back to locked_vm being the value checked against
> > RLIMIT_MEMLOCK.
>
> Someone would need to understand the bug that was fixed by splitting
> them.
>
My suggestion above assumes that splitting them is required/correct. To be
fair I've not dug into if this is true or not, but I trust Christopher.
What I have found is this commit:
bc3e53f682d9 mm: distinguish between mlocked and pinned pages
I think that commit introduced the bug (for IB) which at the time may have been
"ok" because many users of IB at the time were HPC/MPI users and I don't think
MPI does a lot of _separate_ mlock operations so the count of locked_vm was
probably negligible. Alternatively, the clusters I've worked on in the past
had compute nodes set with RLIMIT_MEMLOCK to 'unlimited' whilst running MPI
applications on compute nodes of a cluster... :-/
I think what Christopher did was probably ok for the internal tracking but we
_should_ have had something which summed the 2 for RLIMIT_MEMLOCK checking at
that time to be 100% correct? Christopher do you remember why you did not do
that?
[1] http://lkml.kernel.org/r/20130524140114.GK23650@twins.programming.kicks-ass.net
>
> I think it had to do with double accounting pinned and mlocked pages
> and thus delivering a lower than expected limit to userspace.
>
> vfio has this bug, RDMA does not. RDMA has a bug where it can
> overallocate locked memory, vfio doesn't.
Wouldn't vfio also be able to overallocate if the user had RDMA pinned pages?
I think the problem is that if the user calls mlock on a large range then both
vfio and RDMA could potentially overallocate even with this fix. This was your
initial email to Daniel, I think... And Alex's concern.
>
> Really unclear how to fix this. The pinned/locked split with two
> buckets may be the right way.
Are you suggesting that we have 2 user limits?
Ira
>
> Jason
next prev parent reply other threads:[~2019-02-14 19:41 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
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 [this message]
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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