Re: [External] Re: [PATCH 0/5] Use obj_cgroup APIs to change kmem pages

[Muchun Song <songmuchun@bytedance.com>]

On Tue, Mar 2, 2021 at 9:12 AM Roman Gushchin <guro@fb.com> wrote:
>
> Hi Muchun!
>
> On Mon, Mar 01, 2021 at 02:22:22PM +0800, Muchun Song wrote:
> > Since Roman series "The new cgroup slab memory controller" applied. All
> > slab objects are changed via the new APIs of obj_cgroup. This new APIs
> > introduce a struct obj_cgroup instead of using struct mem_cgroup directly
> > to charge slab objects. It prevents long-living objects from pinning the
> > original memory cgroup in the memory. But there are still some corner
> > objects (e.g. allocations larger than order-1 page on SLUB) which are
> > not charged via the API of obj_cgroup. Those objects (include the pages
> > which are allocated from buddy allocator directly) are charged as kmem
> > pages which still hold a reference to the memory cgroup.
>
> Yes, this is a good idea, large kmallocs should be treated the same
> way as small ones.
>
> >
> > E.g. We know that the kernel stack is charged as kmem pages because the
> > size of the kernel stack can be greater than 2 pages (e.g. 16KB on x86_64
> > or arm64). If we create a thread (suppose the thread stack is charged to
> > memory cgroup A) and then move it from memory cgroup A to memory cgroup
> > B. Because the kernel stack of the thread hold a reference to the memory
> > cgroup A. The thread can pin the memory cgroup A in the memory even if
> > we remove the cgroup A. If we want to see this scenario by using the
> > following script. We can see that the system has added 500 dying cgroups.
> >
> >       #!/bin/bash
> >
> >       cat /proc/cgroups | grep memory
> >
> >       cd /sys/fs/cgroup/memory
> >       echo 1 > memory.move_charge_at_immigrate
> >
> >       for i in range{1..500}
> >       do
> >               mkdir kmem_test
> >               echo $$ > kmem_test/cgroup.procs
> >               sleep 3600 &
> >               echo $$ > cgroup.procs
> >               echo `cat kmem_test/cgroup.procs` > cgroup.procs
> >               rmdir kmem_test
> >       done
> >
> >       cat /proc/cgroups | grep memory
>
> Well, moving processes between cgroups always created a lot of issues
> and corner cases and this one is definitely not the worst. So this problem
> looks a bit artificial, unless I'm missing something. But if it doesn't
> introduce any new performance costs and doesn't make the code more complex,
> I have nothing against.

OK. I just want to show that large kmallocs are charged as kmem pages.
So I constructed this test case.

>
> Btw, can you, please, run the spell-checker on commit logs? There are many
> typos (starting from the title of the series, I guess), which make the patchset
> look less appealing.

Sorry for my poor English. I will do that. Thanks for your suggestions.


>
> Thank you!
>
> >
> > This patchset aims to make those kmem pages drop the reference to memory
> > cgroup by using the APIs of obj_cgroup. Finally, we can see that the number
> > of the dying cgroups will not increase if we run the above test script.
> >
> > Patch 1-3 are using obj_cgroup APIs to charge kmem pages. The remote
> > memory cgroup charing APIs is a mechanism to charge kernel memory to a
> > given memory cgroup. So I also make it use the APIs of obj_cgroup.
> > Patch 4-5 are doing this.
> >
> > Muchun Song (5):
> >   mm: memcontrol: introduce obj_cgroup_{un}charge_page
> >   mm: memcontrol: make page_memcg{_rcu} only applicable for non-kmem
> >     page
> >   mm: memcontrol: reparent the kmem pages on cgroup removal
> >   mm: memcontrol: move remote memcg charging APIs to CONFIG_MEMCG_KMEM
> >   mm: memcontrol: use object cgroup for remote memory cgroup charging
> >
> >  fs/buffer.c                          |  10 +-
> >  fs/notify/fanotify/fanotify.c        |   6 +-
> >  fs/notify/fanotify/fanotify_user.c   |   2 +-
> >  fs/notify/group.c                    |   3 +-
> >  fs/notify/inotify/inotify_fsnotify.c |   8 +-
> >  fs/notify/inotify/inotify_user.c     |   2 +-
> >  include/linux/bpf.h                  |   2 +-
> >  include/linux/fsnotify_backend.h     |   2 +-
> >  include/linux/memcontrol.h           | 109 +++++++++++---
> >  include/linux/sched.h                |   6 +-
> >  include/linux/sched/mm.h             |  30 ++--
> >  kernel/bpf/syscall.c                 |  35 ++---
> >  kernel/fork.c                        |   4 +-
> >  mm/memcontrol.c                      | 276 ++++++++++++++++++++++-------------
> >  mm/page_alloc.c                      |   4 +-
> >  15 files changed, 324 insertions(+), 175 deletions(-)
> >
> > --
> > 2.11.0
> >