[bpf-next,v5,00/34] bpf: switch to memcg-based memory accounting

Currently bpf is using the memlock rlimit for the memory accounting.
This approach has its downsides and over time has created a significant
amount of problems:

1) The limit is per-user, but because most bpf operations are performed
   as root, the limit has a little value.

2) It's hard to come up with a specific maximum value. Especially because
   the counter is shared with non-bpf users (e.g. memlock() users).
   Any specific value is either too low and creates false failures
   or too high and useless.

3) Charging is not connected to the actual memory allocation. Bpf code
   should manually calculate the estimated cost and precharge the counter,
   and then take care of uncharging, including all fail paths.
   It adds to the code complexity and makes it easy to leak a charge.

4) There is no simple way of getting the current value of the counter.
   We've used drgn for it, but it's far from being convenient.

5) Cryptic -EPERM is returned on exceeding the limit. Libbpf even had
   a function to "explain" this case for users.

In order to overcome these problems let's switch to the memcg-based
memory accounting of bpf objects. With the recent addition of the percpu
memory accounting, now it's possible to provide a comprehensive accounting
of the memory used by bpf programs and maps.

This approach has the following advantages:
1) The limit is per-cgroup and hierarchical. It's way more flexible and allows
   a better control over memory usage by different workloads. Of course, it
   requires enabled cgroups and kernel memory accounting and properly configured
   cgroup tree, but it's a default configuration for a modern Linux system.

2) The actual memory consumption is taken into account. It happens automatically
   on the allocation time if __GFP_ACCOUNT flags is passed. Uncharging is also
   performed automatically on releasing the memory. So the code on the bpf side
   becomes simpler and safer.

3) There is a simple way to get the current value and statistics.

In general, if a process performs a bpf operation (e.g. creates or updates
a map), it's memory cgroup is charged. However map updates performed from
an interrupt context are charged to the memory cgroup which contained
the process, which created the map.

Providing a 1:1 replacement for the rlimit-based memory accounting is
a non-goal of this patchset. Users and memory cgroups are completely
orthogonal, so it's not possible even in theory.
Memcg-based memory accounting requires a properly configured cgroup tree
to be actually useful. However, it's the way how the memory is managed
on a modern Linux system.


The patchset consists of the following parts:
1) 4 mm patches, which are already in the mm tree, but are required
   to avoid a regression (otherwise vmallocs cannot be mapped to userspace).
2) memcg-based accounting for various bpf objects: progs and maps
3) removal of the rlimit-based accounting
4) removal of rlimit adjustments in userspace samples

First 4 patches are not supposed to be merged via the bpf tree. I'm including
them to make sure bpf tests will pass.

v5:
  - rebased to the latest version of the remote charging API
  - implemented kmem accounting from an interrupt context, by Shakeel
  - rebased to latest changes in mm allowed to map vmallocs to userspace
  - fixed a build issue in kselftests, by Alexei
  - fixed a use-after-free bug in bpf_map_free_deferred()
  - added bpf line info coverage, by Shakeel
  - split bpf map charging preparations into a separate patch

v4:
  - covered allocations made from an interrupt context, by Daniel
  - added some clarifications to the cover letter

v3:
  - droped the userspace part for further discussions/refinements,
    by Andrii and Song

v2:
  - fixed build issue, caused by the remaining rlimit-based accounting
    for sockhash maps


Roman Gushchin (34):
  mm: memcontrol: use helpers to read page's memcg data
  mm: memcontrol/slab: use helpers to access slab page's memcg_data
  mm: introduce page memcg flags
  mm: convert page kmemcg type to a page memcg flag
  bpf: memcg-based memory accounting for bpf progs
  bpf: prepare for memcg-based memory accounting for bpf maps
  bpf: memcg-based memory accounting for bpf maps
  bpf: refine memcg-based memory accounting for arraymap maps
  bpf: refine memcg-based memory accounting for cpumap maps
  bpf: memcg-based memory accounting for cgroup storage maps
  bpf: refine memcg-based memory accounting for devmap maps
  bpf: refine memcg-based memory accounting for hashtab maps
  bpf: memcg-based memory accounting for lpm_trie maps
  bpf: memcg-based memory accounting for bpf ringbuffer
  bpf: memcg-based memory accounting for bpf local storage maps
  bpf: refine memcg-based memory accounting for sockmap and sockhash
    maps
  bpf: refine memcg-based memory accounting for xskmap maps
  bpf: eliminate rlimit-based memory accounting for arraymap maps
  bpf: eliminate rlimit-based memory accounting for bpf_struct_ops maps
  bpf: eliminate rlimit-based memory accounting for cpumap maps
  bpf: eliminate rlimit-based memory accounting for cgroup storage maps
  bpf: eliminate rlimit-based memory accounting for devmap maps
  bpf: eliminate rlimit-based memory accounting for hashtab maps
  bpf: eliminate rlimit-based memory accounting for lpm_trie maps
  bpf: eliminate rlimit-based memory accounting for queue_stack_maps
    maps
  bpf: eliminate rlimit-based memory accounting for reuseport_array maps
  bpf: eliminate rlimit-based memory accounting for bpf ringbuffer
  bpf: eliminate rlimit-based memory accounting for sockmap and sockhash
    maps
  bpf: eliminate rlimit-based memory accounting for stackmap maps
  bpf: eliminate rlimit-based memory accounting for xskmap maps
  bpf: eliminate rlimit-based memory accounting for bpf local storage
    maps
  bpf: eliminate rlimit-based memory accounting infra for bpf maps
  bpf: eliminate rlimit-based memory accounting for bpf progs
  bpf: samples: do not touch RLIMIT_MEMLOCK

 fs/buffer.c                                   |   2 +-
 fs/iomap/buffered-io.c                        |   2 +-
 include/linux/bpf.h                           |  27 +--
 include/linux/memcontrol.h                    | 215 +++++++++++++++++-
 include/linux/mm.h                            |  22 --
 include/linux/mm_types.h                      |   5 +-
 include/linux/page-flags.h                    |  11 +-
 include/trace/events/writeback.h              |   2 +-
 kernel/bpf/arraymap.c                         |  30 +--
 kernel/bpf/bpf_local_storage.c                |  18 +-
 kernel/bpf/bpf_struct_ops.c                   |  19 +-
 kernel/bpf/core.c                             |  22 +-
 kernel/bpf/cpumap.c                           |  20 +-
 kernel/bpf/devmap.c                           |  23 +-
 kernel/bpf/hashtab.c                          |  33 +--
 kernel/bpf/helpers.c                          |  37 ++-
 kernel/bpf/local_storage.c                    |  38 +---
 kernel/bpf/lpm_trie.c                         |  17 +-
 kernel/bpf/queue_stack_maps.c                 |  16 +-
 kernel/bpf/reuseport_array.c                  |  12 +-
 kernel/bpf/ringbuf.c                          |  33 +--
 kernel/bpf/stackmap.c                         |  16 +-
 kernel/bpf/syscall.c                          | 177 ++++----------
 kernel/fork.c                                 |   7 +-
 mm/debug.c                                    |   4 +-
 mm/huge_memory.c                              |   4 +-
 mm/memcontrol.c                               | 139 +++++------
 mm/page_alloc.c                               |   8 +-
 mm/page_io.c                                  |   6 +-
 mm/slab.h                                     |  38 +---
 mm/workingset.c                               |   2 +-
 net/core/bpf_sk_storage.c                     |   2 +-
 net/core/sock_map.c                           |  40 +---
 net/xdp/xskmap.c                              |  15 +-
 samples/bpf/map_perf_test_user.c              |   6 -
 samples/bpf/offwaketime_user.c                |   6 -
 samples/bpf/sockex2_user.c                    |   2 -
 samples/bpf/sockex3_user.c                    |   2 -
 samples/bpf/spintest_user.c                   |   6 -
 samples/bpf/syscall_tp_user.c                 |   2 -
 samples/bpf/task_fd_query_user.c              |   5 -
 samples/bpf/test_lru_dist.c                   |   3 -
 samples/bpf/test_map_in_map_user.c            |   6 -
 samples/bpf/test_overhead_user.c              |   2 -
 samples/bpf/trace_event_user.c                |   2 -
 samples/bpf/tracex2_user.c                    |   6 -
 samples/bpf/tracex3_user.c                    |   6 -
 samples/bpf/tracex4_user.c                    |   6 -
 samples/bpf/tracex5_user.c                    |   3 -
 samples/bpf/tracex6_user.c                    |   3 -
 samples/bpf/xdp1_user.c                       |   6 -
 samples/bpf/xdp_adjust_tail_user.c            |   6 -
 samples/bpf/xdp_monitor_user.c                |   5 -
 samples/bpf/xdp_redirect_cpu_user.c           |   6 -
 samples/bpf/xdp_redirect_map_user.c           |   6 -
 samples/bpf/xdp_redirect_user.c               |   6 -
 samples/bpf/xdp_router_ipv4_user.c            |   6 -
 samples/bpf/xdp_rxq_info_user.c               |   6 -
 samples/bpf/xdp_sample_pkts_user.c            |   6 -
 samples/bpf/xdp_tx_iptunnel_user.c            |   6 -
 samples/bpf/xdpsock_user.c                    |   7 -
 .../selftests/bpf/progs/bpf_iter_bpf_map.c    |   2 +-
 .../selftests/bpf/progs/map_ptr_kern.c        |   7 -
 63 files changed, 460 insertions(+), 743 deletions(-)

Hi Roman,

On Thu, 12 Nov 2020 14:15:10 -0800 Roman Gushchin <guro@fb.com> wrote:
>
> Patch series "mm: allow mapping accounted kernel pages to userspace", v6.
> 
> Currently a non-slab kernel page which has been charged to a memory cgroup
> can't be mapped to userspace.  The underlying reason is simple: PageKmemcg
> flag is defined as a page type (like buddy, offline, etc), so it takes a
> bit from a page->mapped counter.  Pages with a type set can't be mapped to
> userspace.
>
.....
> 
> To make sure nobody uses a direct access, struct page's
> mem_cgroup/obj_cgroups is converted to unsigned long memcg_data.
> 
> Link: https://lkml.kernel.org/r/20201027001657.3398190-1-guro@fb.com
> Link: https://lkml.kernel.org/r/20201027001657.3398190-2-guro@fb.com
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

What is going on here?  You are taking patches from linux-next and
submitting them to another maintainer?  Why?

You should not do that from Andrew's tree as it changes/rebases every
so often ... and you should not have my SOB on there as it is only
there because that patch is in linux-next i.e. I in the submission
chain to linux-next - if the patch is to go via some other tree, then
my SOB should not be there.  (The same may be true for Andrew's SOB.)
In general you cannot add someone else's SOB to one of your patch
submissions.

On Fri, Nov 13, 2020 at 09:56:32AM +1100, Stephen Rothwell wrote:
> Hi Roman,
> 
> On Thu, 12 Nov 2020 14:15:10 -0800 Roman Gushchin <guro@fb.com> wrote:
> >
> > Patch series "mm: allow mapping accounted kernel pages to userspace", v6.
> > 
> > Currently a non-slab kernel page which has been charged to a memory cgroup
> > can't be mapped to userspace.  The underlying reason is simple: PageKmemcg
> > flag is defined as a page type (like buddy, offline, etc), so it takes a
> > bit from a page->mapped counter.  Pages with a type set can't be mapped to
> > userspace.
> >
> .....
> > 
> > To make sure nobody uses a direct access, struct page's
> > mem_cgroup/obj_cgroups is converted to unsigned long memcg_data.
> > 
> > Link: https://lkml.kernel.org/r/20201027001657.3398190-1-guro@fb.com
> > Link: https://lkml.kernel.org/r/20201027001657.3398190-2-guro@fb.com
> > Signed-off-by: Roman Gushchin <guro@fb.com>
> > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> > Reviewed-by: Shakeel Butt <shakeelb@google.com>
> > Acked-by: Michal Hocko <mhocko@suse.com>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
> 
> What is going on here?  You are taking patches from linux-next and
> submitting them to another maintainer?  Why?

Hi Stephen!

These patches are not intended to be merged through the bpf tree.
They are included into the patchset to make bpf selftests pass and for
informational purposes.
It's written in the cover letter.

> 
> You should not do that from Andrew's tree as it changes/rebases every
> so often ... and you should not have my SOB on there as it is only
> there because that patch is in linux-next i.e. I in the submission
> chain to linux-next - if the patch is to go via some other tree, then
> my SOB should not be there.  (The same may be true for Andrew's SOB.)
> In general you cannot add someone else's SOB to one of your patch
> submissions.

I'm sorry for the confusion.

Maybe I had to just list their titles in the cover letter. Idk what's
the best option for such cross-subsystem dependencies.

Thanks!

On Thu, Nov 12, 2020 at 04:26:10PM -0800, Roman Gushchin wrote:
> 
> These patches are not intended to be merged through the bpf tree.
> They are included into the patchset to make bpf selftests pass and for
> informational purposes.
> It's written in the cover letter.
...
> Maybe I had to just list their titles in the cover letter. Idk what's
> the best option for such cross-subsystem dependencies.

We had several situations in the past releases where dependent patches
were merged into multiple trees. For that to happen cleanly from git pov
one of the maintainers need to create a stable branch/tag and let other
maintainers pull that branch into different trees. This way the sha-s
stay the same and no conflicts arise during the merge window.
In this case sounds like the first 4 patches are in mm tree already.
Is there a branch/tag I can pull to get the first 4 into bpf-next?

On Thu, 12 Nov 2020 19:04:56 -0800 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> On Thu, Nov 12, 2020 at 04:26:10PM -0800, Roman Gushchin wrote:
> > 
> > These patches are not intended to be merged through the bpf tree.
> > They are included into the patchset to make bpf selftests pass and for
> > informational purposes.
> > It's written in the cover letter.
> ...
> > Maybe I had to just list their titles in the cover letter. Idk what's
> > the best option for such cross-subsystem dependencies.
> 
> We had several situations in the past releases where dependent patches
> were merged into multiple trees. For that to happen cleanly from git pov
> one of the maintainers need to create a stable branch/tag and let other
> maintainers pull that branch into different trees. This way the sha-s
> stay the same and no conflicts arise during the merge window.
> In this case sounds like the first 4 patches are in mm tree already.
> Is there a branch/tag I can pull to get the first 4 into bpf-next?

Not really, at present.  This is largely by design, although it does cause
this problem once or twice a year.

These four patches:

mm-memcontrol-use-helpers-to-read-pages-memcg-data.patch
mm-memcontrol-slab-use-helpers-to-access-slab-pages-memcg_data.patch
mm-introduce-page-memcg-flags.patch
mm-convert-page-kmemcg-type-to-a-page-memcg-flag.patch

are sufficiently reviewed - please pull them into the bpf tree when
convenient.  Once they hit linux-next, I'll drop the -mm copies and the
bpf tree maintainers will then be responsible for whether & when they
get upstream.

On Thu, Nov 12, 2020 at 7:18 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 12 Nov 2020 19:04:56 -0800 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
>
> > On Thu, Nov 12, 2020 at 04:26:10PM -0800, Roman Gushchin wrote:
> > >
> > > These patches are not intended to be merged through the bpf tree.
> > > They are included into the patchset to make bpf selftests pass and for
> > > informational purposes.
> > > It's written in the cover letter.
> > ...
> > > Maybe I had to just list their titles in the cover letter. Idk what's
> > > the best option for such cross-subsystem dependencies.
> >
> > We had several situations in the past releases where dependent patches
> > were merged into multiple trees. For that to happen cleanly from git pov
> > one of the maintainers need to create a stable branch/tag and let other
> > maintainers pull that branch into different trees. This way the sha-s
> > stay the same and no conflicts arise during the merge window.
> > In this case sounds like the first 4 patches are in mm tree already.
> > Is there a branch/tag I can pull to get the first 4 into bpf-next?
>
> Not really, at present.  This is largely by design, although it does cause
> this problem once or twice a year.
>
> These four patches:
>
> mm-memcontrol-use-helpers-to-read-pages-memcg-data.patch
> mm-memcontrol-slab-use-helpers-to-access-slab-pages-memcg_data.patch
> mm-introduce-page-memcg-flags.patch
> mm-convert-page-kmemcg-type-to-a-page-memcg-flag.patch
>
> are sufficiently reviewed - please pull them into the bpf tree when
> convenient.  Once they hit linux-next, I'll drop the -mm copies and the
> bpf tree maintainers will then be responsible for whether & when they
> get upstream.

That's certainly an option if they don't depend on other patches in the mm tree.
Roman probably knows best ?

On Thu, 12 Nov 2020 19:25:48 -0800 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> On Thu, Nov 12, 2020 at 7:18 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Thu, 12 Nov 2020 19:04:56 -0800 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> >
> > > On Thu, Nov 12, 2020 at 04:26:10PM -0800, Roman Gushchin wrote:
> > > >
> > > > These patches are not intended to be merged through the bpf tree.
> > > > They are included into the patchset to make bpf selftests pass and for
> > > > informational purposes.
> > > > It's written in the cover letter.
> > > ...
> > > > Maybe I had to just list their titles in the cover letter. Idk what's
> > > > the best option for such cross-subsystem dependencies.
> > >
> > > We had several situations in the past releases where dependent patches
> > > were merged into multiple trees. For that to happen cleanly from git pov
> > > one of the maintainers need to create a stable branch/tag and let other
> > > maintainers pull that branch into different trees. This way the sha-s
> > > stay the same and no conflicts arise during the merge window.
> > > In this case sounds like the first 4 patches are in mm tree already.
> > > Is there a branch/tag I can pull to get the first 4 into bpf-next?
> >
> > Not really, at present.  This is largely by design, although it does cause
> > this problem once or twice a year.
> >
> > These four patches:
> >
> > mm-memcontrol-use-helpers-to-read-pages-memcg-data.patch
> > mm-memcontrol-slab-use-helpers-to-access-slab-pages-memcg_data.patch
> > mm-introduce-page-memcg-flags.patch
> > mm-convert-page-kmemcg-type-to-a-page-memcg-flag.patch
> >
> > are sufficiently reviewed - please pull them into the bpf tree when
> > convenient.  Once they hit linux-next, I'll drop the -mm copies and the
> > bpf tree maintainers will then be responsible for whether & when they
> > get upstream.
> 
> That's certainly an option if they don't depend on other patches in the mm tree.
> Roman probably knows best ?

That should be OK.  They apply and compile ;)

On Thu, Nov 12, 2020 at 07:25:48PM -0800, Alexei Starovoitov wrote:
> On Thu, Nov 12, 2020 at 7:18 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Thu, 12 Nov 2020 19:04:56 -0800 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> >
> > > On Thu, Nov 12, 2020 at 04:26:10PM -0800, Roman Gushchin wrote:
> > > >
> > > > These patches are not intended to be merged through the bpf tree.
> > > > They are included into the patchset to make bpf selftests pass and for
> > > > informational purposes.
> > > > It's written in the cover letter.
> > > ...
> > > > Maybe I had to just list their titles in the cover letter. Idk what's
> > > > the best option for such cross-subsystem dependencies.
> > >
> > > We had several situations in the past releases where dependent patches
> > > were merged into multiple trees. For that to happen cleanly from git pov
> > > one of the maintainers need to create a stable branch/tag and let other
> > > maintainers pull that branch into different trees. This way the sha-s
> > > stay the same and no conflicts arise during the merge window.
> > > In this case sounds like the first 4 patches are in mm tree already.
> > > Is there a branch/tag I can pull to get the first 4 into bpf-next?
> >
> > Not really, at present.  This is largely by design, although it does cause
> > this problem once or twice a year.
> >
> > These four patches:
> >
> > mm-memcontrol-use-helpers-to-read-pages-memcg-data.patch
> > mm-memcontrol-slab-use-helpers-to-access-slab-pages-memcg_data.patch
> > mm-introduce-page-memcg-flags.patch
> > mm-convert-page-kmemcg-type-to-a-page-memcg-flag.patch
> >
> > are sufficiently reviewed - please pull them into the bpf tree when
> > convenient.  Once they hit linux-next, I'll drop the -mm copies and the
> > bpf tree maintainers will then be responsible for whether & when they
> > get upstream.
> 
> That's certainly an option if they don't depend on other patches in the mm tree.
> Roman probably knows best ?

Yes, they are self-contained and don't depend on any patches in the mm tree.

Thanks!

On Thu, Nov 12, 2020 at 7:40 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 12 Nov 2020 19:25:48 -0800 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
>
> > On Thu, Nov 12, 2020 at 7:18 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> > >
> > > On Thu, 12 Nov 2020 19:04:56 -0800 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> > >
> > > > On Thu, Nov 12, 2020 at 04:26:10PM -0800, Roman Gushchin wrote:
> > > > >
> > > > > These patches are not intended to be merged through the bpf tree.
> > > > > They are included into the patchset to make bpf selftests pass and for
> > > > > informational purposes.
> > > > > It's written in the cover letter.
> > > > ...
> > > > > Maybe I had to just list their titles in the cover letter. Idk what's
> > > > > the best option for such cross-subsystem dependencies.
> > > >
> > > > We had several situations in the past releases where dependent patches
> > > > were merged into multiple trees. For that to happen cleanly from git pov
> > > > one of the maintainers need to create a stable branch/tag and let other
> > > > maintainers pull that branch into different trees. This way the sha-s
> > > > stay the same and no conflicts arise during the merge window.
> > > > In this case sounds like the first 4 patches are in mm tree already.
> > > > Is there a branch/tag I can pull to get the first 4 into bpf-next?
> > >
> > > Not really, at present.  This is largely by design, although it does cause
> > > this problem once or twice a year.
> > >
> > > These four patches:
> > >
> > > mm-memcontrol-use-helpers-to-read-pages-memcg-data.patch
> > > mm-memcontrol-slab-use-helpers-to-access-slab-pages-memcg_data.patch
> > > mm-introduce-page-memcg-flags.patch
> > > mm-convert-page-kmemcg-type-to-a-page-memcg-flag.patch
> > >
> > > are sufficiently reviewed - please pull them into the bpf tree when
> > > convenient.  Once they hit linux-next, I'll drop the -mm copies and the
> > > bpf tree maintainers will then be responsible for whether & when they
> > > get upstream.
> >
> > That's certainly an option if they don't depend on other patches in the mm tree.
> > Roman probably knows best ?
>
> That should be OK.  They apply and compile ;)

Awesome. Thank you both for confirming.
Will take them as soon as the rest of the set is reviewed.

On Thu, Nov 12, 2020 at 8:02 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Thu, Nov 12, 2020 at 07:25:48PM -0800, Alexei Starovoitov wrote:
> > On Thu, Nov 12, 2020 at 7:18 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> > >
> > > On Thu, 12 Nov 2020 19:04:56 -0800 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> > >
> > > > On Thu, Nov 12, 2020 at 04:26:10PM -0800, Roman Gushchin wrote:
> > > > >
> > > > > These patches are not intended to be merged through the bpf tree.
> > > > > They are included into the patchset to make bpf selftests pass and for
> > > > > informational purposes.
> > > > > It's written in the cover letter.
> > > > ...
> > > > > Maybe I had to just list their titles in the cover letter. Idk what's
> > > > > the best option for such cross-subsystem dependencies.
> > > >
> > > > We had several situations in the past releases where dependent patches
> > > > were merged into multiple trees. For that to happen cleanly from git pov
> > > > one of the maintainers need to create a stable branch/tag and let other
> > > > maintainers pull that branch into different trees. This way the sha-s
> > > > stay the same and no conflicts arise during the merge window.
> > > > In this case sounds like the first 4 patches are in mm tree already.
> > > > Is there a branch/tag I can pull to get the first 4 into bpf-next?
> > >
> > > Not really, at present.  This is largely by design, although it does cause
> > > this problem once or twice a year.
> > >
> > > These four patches:
> > >
> > > mm-memcontrol-use-helpers-to-read-pages-memcg-data.patch
> > > mm-memcontrol-slab-use-helpers-to-access-slab-pages-memcg_data.patch
> > > mm-introduce-page-memcg-flags.patch
> > > mm-convert-page-kmemcg-type-to-a-page-memcg-flag.patch
> > >
> > > are sufficiently reviewed - please pull them into the bpf tree when
> > > convenient.  Once they hit linux-next, I'll drop the -mm copies and the
> > > bpf tree maintainers will then be responsible for whether & when they
> > > get upstream.
> >
> > That's certainly an option if they don't depend on other patches in the mm tree.
> > Roman probably knows best ?
>
> Yes, they are self-contained and don't depend on any patches in the mm tree.
>

The patch "mm, kvm: account kvm_vcpu_mmap to kmemcg" in mm tree
depends on that series.

On Fri, Nov 13, 2020 at 06:25:53AM -0800, Shakeel Butt wrote:
> On Thu, Nov 12, 2020 at 8:02 PM Roman Gushchin <guro@fb.com> wrote:
> >
> > On Thu, Nov 12, 2020 at 07:25:48PM -0800, Alexei Starovoitov wrote:
> > > On Thu, Nov 12, 2020 at 7:18 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> > > >
> > > > On Thu, 12 Nov 2020 19:04:56 -0800 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> > > >
> > > > > On Thu, Nov 12, 2020 at 04:26:10PM -0800, Roman Gushchin wrote:
> > > > > >
> > > > > > These patches are not intended to be merged through the bpf tree.
> > > > > > They are included into the patchset to make bpf selftests pass and for
> > > > > > informational purposes.
> > > > > > It's written in the cover letter.
> > > > > ...
> > > > > > Maybe I had to just list their titles in the cover letter. Idk what's
> > > > > > the best option for such cross-subsystem dependencies.
> > > > >
> > > > > We had several situations in the past releases where dependent patches
> > > > > were merged into multiple trees. For that to happen cleanly from git pov
> > > > > one of the maintainers need to create a stable branch/tag and let other
> > > > > maintainers pull that branch into different trees. This way the sha-s
> > > > > stay the same and no conflicts arise during the merge window.
> > > > > In this case sounds like the first 4 patches are in mm tree already.
> > > > > Is there a branch/tag I can pull to get the first 4 into bpf-next?
> > > >
> > > > Not really, at present.  This is largely by design, although it does cause
> > > > this problem once or twice a year.
> > > >
> > > > These four patches:
> > > >
> > > > mm-memcontrol-use-helpers-to-read-pages-memcg-data.patch
> > > > mm-memcontrol-slab-use-helpers-to-access-slab-pages-memcg_data.patch
> > > > mm-introduce-page-memcg-flags.patch
> > > > mm-convert-page-kmemcg-type-to-a-page-memcg-flag.patch
> > > >
> > > > are sufficiently reviewed - please pull them into the bpf tree when
> > > > convenient.  Once they hit linux-next, I'll drop the -mm copies and the
> > > > bpf tree maintainers will then be responsible for whether & when they
> > > > get upstream.
> > >
> > > That's certainly an option if they don't depend on other patches in the mm tree.
> > > Roman probably knows best ?
> >
> > Yes, they are self-contained and don't depend on any patches in the mm tree.
> >
> 
> The patch "mm, kvm: account kvm_vcpu_mmap to kmemcg" in mm tree
> depends on that series.

True, and I believe there are (or will be) more dependencies like this.
But it should be fine, we only have to make sure that these 4 patches
will be merged first.

Thanks!