From: Jason Gunthorpe <jgg@nvidia.com>
To: Tejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>,
Yosry Ahmed <yosryahmed@google.com>,
Alistair Popple <apopple@nvidia.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, jhubbard@nvidia.com,
tjmercier@google.com, hannes@cmpxchg.org, surenb@google.com,
mkoutny@suse.com, daniel@ffwll.ch,
"Daniel P . Berrange" <berrange@redhat.com>,
Alex Williamson <alex.williamson@redhat.com>,
Zefan Li <lizefan.x@bytedance.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 14/19] mm: Introduce a cgroup for pinned memory
Date: Tue, 21 Feb 2023 15:57:54 -0400 [thread overview]
Message-ID: <Y/UiQmuVwh2eqrfA@nvidia.com> (raw)
In-Reply-To: <Y/UfS8TDIXhUlJ/I@slm.duckdns.org>
On Tue, Feb 21, 2023 at 09:45:15AM -1000, Tejun Heo wrote:
> Hello,
>
> On Tue, Feb 21, 2023 at 03:26:33PM -0400, Jason Gunthorpe wrote:
> > On Tue, Feb 21, 2023 at 08:07:13AM -1000, Tejun Heo wrote:
> > > > AFAIK there are few real use cases to establish a pin on MAP_SHARED
> > > > mappings outside your cgroup. However, it is possible, the APIs allow
> > > > it, and for security sandbox purposes we can't allow a process inside
> > > > a cgroup to triger a charge on a different cgroup. That breaks the
> > > > sandbox goal.
> > >
> > > It seems broken anyway. Please consider the following scenario:
> >
> > Yes, this is broken like this already today - memcg doesn't work
> > entirely perfectly for MAP_SHARED scenarios, IMHO.
>
> It is far from perfect but the existing behavior isn't that broken. e.g. in
> the same scenario, without pinning, even if the larger cgroup keeps using
> the same page, the smaller cgroup should be able to evict the pages as they
> are not pinned and the cgroup is under heavy reclaim pressure. The larger
> cgroup will refault them back in and end up owning those pages.
>
> memcg can't capture the case of the same pages being actively shared by
> multiple cgroups concurrently (I think those cases should be handled by
> pushing them to the common parent as discussed elswhere but that's a
> separate topic) but it can converge when page usage transfers across cgroups
> if needed. Disassociating ownership and pinning will break that in an
> irreversible way.
It is already disassociated - memcg is broken as you describe today
with pin_user_pages().
If you want to fix that, then we need to redefine how memcg works with
pin_user_pages() and I'm open to ideas..
> the owner and pinner disagreeing with each other. At least
> conceptually, the solution is rather straight-forward - whoever pins
> a page should also claim the ownership of it.
If the answer is pinner is owner, then multi-pinners must mean
multi-owner too. We probably can't block multi-pinner without causing
uAPI problems.
You are not wrong on any of these remarks, but this looses sight of
the point - it is take the existing broken RLIMIT scheme and make it
incrementally better by being the same broken scheme just with
cgroups.
If we eventually fix everything so memcg can do multi-pinners/owners
then would it be reasonable to phase out the new pincg at that time?
Jason
next prev parent reply other threads:[~2023-02-21 19:58 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-06 7:47 [PATCH 00/19] mm: Introduce a cgroup to limit the amount of locked and pinned memory Alistair Popple
2023-02-06 7:47 ` [PATCH 01/19] mm: Introduce vm_account Alistair Popple
2023-02-06 7:47 ` [PATCH 02/19] drivers/vhost: Convert to use vm_account Alistair Popple
2023-02-06 7:47 ` [PATCH 03/19] drivers/vdpa: Convert vdpa to use the new vm_structure Alistair Popple
2023-02-06 7:47 ` [PATCH 04/19] infiniband/umem: Convert to use vm_account Alistair Popple
2023-02-06 7:47 ` [PATCH 05/19] RMDA/siw: " Alistair Popple
2023-02-12 17:32 ` Bernard Metzler
2023-02-06 7:47 ` [PATCH 06/19] RDMA/usnic: convert " Alistair Popple
2023-02-06 7:47 ` [PATCH 07/19] vfio/type1: Charge pinned pages to pinned_vm instead of locked_vm Alistair Popple
2023-02-06 7:47 ` [PATCH 08/19] vfio/spapr_tce: Convert accounting to pinned_vm Alistair Popple
2023-02-06 7:47 ` [PATCH 09/19] io_uring: convert to use vm_account Alistair Popple
2023-02-06 15:29 ` Jens Axboe
2023-02-07 1:03 ` Alistair Popple
2023-02-07 14:28 ` Jens Axboe
2023-02-07 14:55 ` Jason Gunthorpe
2023-02-07 17:05 ` Jens Axboe
2023-02-13 11:30 ` Alistair Popple
2023-02-06 7:47 ` [PATCH 10/19] net: skb: Switch to using vm_account Alistair Popple
2023-02-06 7:47 ` [PATCH 11/19] xdp: convert to use vm_account Alistair Popple
2023-02-06 7:47 ` [PATCH 12/19] kvm/book3s_64_vio: Convert account_locked_vm() to vm_account_pinned() Alistair Popple
2023-02-06 7:47 ` [PATCH 13/19] fpga: dfl: afu: convert to use vm_account Alistair Popple
2023-02-06 7:47 ` [PATCH 14/19] mm: Introduce a cgroup for pinned memory Alistair Popple
2023-02-06 21:01 ` Yosry Ahmed
2023-02-06 21:14 ` Tejun Heo
2023-02-06 22:32 ` Yosry Ahmed
2023-02-06 22:36 ` Tejun Heo
2023-02-06 22:39 ` Yosry Ahmed
2023-02-06 23:25 ` Tejun Heo
2023-02-06 23:34 ` Yosry Ahmed
2023-02-06 23:40 ` Jason Gunthorpe
2023-02-07 0:32 ` Tejun Heo
2023-02-07 12:19 ` Jason Gunthorpe
2023-02-15 19:00 ` Michal Hocko
2023-02-15 19:07 ` Jason Gunthorpe
2023-02-16 8:04 ` Michal Hocko
2023-02-16 12:45 ` Jason Gunthorpe
2023-02-21 16:51 ` Tejun Heo
2023-02-21 17:25 ` Jason Gunthorpe
2023-02-21 17:29 ` Tejun Heo
2023-02-21 17:51 ` Jason Gunthorpe
2023-02-21 18:07 ` Tejun Heo
2023-02-21 19:26 ` Jason Gunthorpe
2023-02-21 19:45 ` Tejun Heo
2023-02-21 19:49 ` Tejun Heo
2023-02-21 19:57 ` Jason Gunthorpe [this message]
2023-02-22 11:38 ` Alistair Popple
2023-02-22 12:57 ` Jason Gunthorpe
2023-02-22 22:59 ` Alistair Popple
2023-02-23 0:05 ` Christoph Hellwig
2023-02-23 0:35 ` Alistair Popple
2023-02-23 1:53 ` Jason Gunthorpe
2023-02-23 9:12 ` Daniel P. Berrangé
2023-02-23 17:31 ` Jason Gunthorpe
2023-02-23 17:18 ` T.J. Mercier
2023-02-23 17:28 ` Jason Gunthorpe
2023-02-23 18:03 ` Yosry Ahmed
2023-02-23 18:10 ` Jason Gunthorpe
2023-02-23 18:14 ` Yosry Ahmed
2023-02-23 18:15 ` Tejun Heo
2023-02-23 18:17 ` Jason Gunthorpe
2023-02-23 18:22 ` Tejun Heo
2023-02-07 1:00 ` Waiman Long
2023-02-07 1:03 ` Tejun Heo
2023-02-07 1:50 ` Alistair Popple
2023-02-06 7:47 ` [PATCH 15/19] mm/util: Extend vm_account to charge pages against the pin cgroup Alistair Popple
2023-02-06 7:47 ` [PATCH 16/19] mm/util: Refactor account_locked_vm Alistair Popple
2023-02-06 7:47 ` [PATCH 17/19] mm: Convert mmap and mlock to use account_locked_vm Alistair Popple
2023-02-06 7:47 ` [PATCH 18/19] mm/mmap: Charge locked memory to pins cgroup Alistair Popple
2023-02-06 21:12 ` Yosry Ahmed
2023-02-06 7:47 ` [PATCH 19/19] selftests/vm: Add pins-cgroup selftest for mlock/mmap Alistair Popple
2023-02-16 11:01 ` [PATCH 00/19] mm: Introduce a cgroup to limit the amount of locked and pinned memory David Hildenbrand
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