Re: [RFC PATCH 00/19] mm: Introduce a cgroup to limit the amount of locked and pinned memory

[Yosry Ahmed]

On Mon, Jan 23, 2023 at 9:43 PM Alistair Popple <apopple@xxxxxxxxxx> wrote:
>
> Having large amounts of unmovable or unreclaimable memory in a system
> can lead to system instability due to increasing the likelihood of
> encountering out-of-memory conditions. Therefore it is desirable to
> limit the amount of memory users can lock or pin.
>
> From userspace such limits can be enforced by setting
> RLIMIT_MEMLOCK. However there is no standard method that drivers and
> other in-kernel users can use to check and enforce this limit.
>
> This has lead to a large number of inconsistencies in how limits are
> enforced. For example some drivers will use mm->locked_mm while others
> will use mm->pinned_mm or user->locked_mm. It is therefore possible to
> have up to three times RLIMIT_MEMLOCKED pinned.
>
> Having pinned memory limited per-task also makes it easy for users to
> exceed the limit. For example drivers that pin memory with
> pin_user_pages() it tends to remain pinned after fork. To deal with
> this and other issues this series introduces a cgroup for tracking and
> limiting the number of pages pinned or locked by tasks in the group.
>
> However the existing behaviour with regards to the rlimit needs to be
> maintained. Therefore the lesser of the two limits is
> enforced. Furthermore having CAP_IPC_LOCK usually bypasses the rlimit,
> but this bypass is not allowed for the cgroup.
>
> The first part of this series converts existing drivers which
> open-code the use of locked_mm/pinned_mm over to a common interface
> which manages the refcounts of the associated task/mm/user
> structs. This ensures accounting of pages is consistent and makes it
> easier to add charging of the cgroup.
>
> The second part of the series adds the cgroup and converts core mm
> code such as mlock over to charging the cgroup before finally
> introducing some selftests.


I didn't go through the entire series, so apologies if this was
mentioned somewhere, but do you mind elaborating on why this is added
as a separate cgroup controller rather than an extension of the memory
cgroup controller?

>
>
> As I don't have access to systems with all the various devices I
> haven't been able to test all driver changes. Any help there would be
> appreciated.
>
> Alistair Popple (19):
>   mm: Introduce vm_account
>   drivers/vhost: Convert to use vm_account
>   drivers/vdpa: Convert vdpa to use the new vm_structure
>   infiniband/umem: Convert to use vm_account
>   RMDA/siw: Convert to use vm_account
>   RDMA/usnic: convert to use vm_account
>   vfio/type1: Charge pinned pages to pinned_vm instead of locked_vm
>   vfio/spapr_tce: Convert accounting to pinned_vm
>   io_uring: convert to use vm_account
>   net: skb: Switch to using vm_account
>   xdp: convert to use vm_account
>   kvm/book3s_64_vio: Convert account_locked_vm() to vm_account_pinned()
>   fpga: dfl: afu: convert to use vm_account
>   mm: Introduce a cgroup for pinned memory
>   mm/util: Extend vm_account to charge pages against the pin cgroup
>   mm/util: Refactor account_locked_vm
>   mm: Convert mmap and mlock to use account_locked_vm
>   mm/mmap: Charge locked memory to pins cgroup
>   selftests/vm: Add pins-cgroup selftest for mlock/mmap
>
>  MAINTAINERS                              |   8 +-
>  arch/powerpc/kvm/book3s_64_vio.c         |  10 +-
>  arch/powerpc/mm/book3s64/iommu_api.c     |  29 +--
>  drivers/fpga/dfl-afu-dma-region.c        |  11 +-
>  drivers/fpga/dfl-afu.h                   |   1 +-
>  drivers/infiniband/core/umem.c           |  16 +-
>  drivers/infiniband/core/umem_odp.c       |   6 +-
>  drivers/infiniband/hw/usnic/usnic_uiom.c |  13 +-
>  drivers/infiniband/hw/usnic/usnic_uiom.h |   1 +-
>  drivers/infiniband/sw/siw/siw.h          |   2 +-
>  drivers/infiniband/sw/siw/siw_mem.c      |  20 +--
>  drivers/infiniband/sw/siw/siw_verbs.c    |  15 +-
>  drivers/vdpa/vdpa_user/vduse_dev.c       |  20 +--
>  drivers/vfio/vfio_iommu_spapr_tce.c      |  15 +-
>  drivers/vfio/vfio_iommu_type1.c          |  59 +----
>  drivers/vhost/vdpa.c                     |   9 +-
>  drivers/vhost/vhost.c                    |   2 +-
>  drivers/vhost/vhost.h                    |   1 +-
>  include/linux/cgroup.h                   |  20 ++-
>  include/linux/cgroup_subsys.h            |   4 +-
>  include/linux/io_uring_types.h           |   3 +-
>  include/linux/kvm_host.h                 |   1 +-
>  include/linux/mm.h                       |   5 +-
>  include/linux/mm_types.h                 |  88 ++++++++-
>  include/linux/skbuff.h                   |   6 +-
>  include/net/sock.h                       |   2 +-
>  include/net/xdp_sock.h                   |   2 +-
>  include/rdma/ib_umem.h                   |   1 +-
>  io_uring/io_uring.c                      |  20 +--
>  io_uring/notif.c                         |   4 +-
>  io_uring/notif.h                         |  10 +-
>  io_uring/rsrc.c                          |  38 +---
>  io_uring/rsrc.h                          |   9 +-
>  mm/Kconfig                               |  11 +-
>  mm/Makefile                              |   1 +-
>  mm/internal.h                            |   2 +-
>  mm/mlock.c                               |  76 +------
>  mm/mmap.c                                |  76 +++----
>  mm/mremap.c                              |  54 +++--
>  mm/pins_cgroup.c                         | 273 ++++++++++++++++++++++++-
>  mm/secretmem.c                           |   6 +-
>  mm/util.c                                | 196 +++++++++++++++--
>  net/core/skbuff.c                        |  47 +---
>  net/rds/message.c                        |   9 +-
>  net/xdp/xdp_umem.c                       |  38 +--
>  tools/testing/selftests/vm/Makefile      |   1 +-
>  tools/testing/selftests/vm/pins-cgroup.c | 271 ++++++++++++++++++++++++-
>  virt/kvm/kvm_main.c                      |   3 +-
>  48 files changed, 1114 insertions(+), 401 deletions(-)
>  create mode 100644 mm/pins_cgroup.c
>  create mode 100644 tools/testing/selftests/vm/pins-cgroup.c
>
> base-commit: 2241ab53cbb5cdb08a6b2d4688feb13971058f65
> --
> git-series 0.9.1
>