commit da34a8484d162585e22ed8c1e4114aa2f60e3567 upstream.
Charge moving mode in cgroup1 allows memory to follow tasks as they
migrate between cgroups. This is, and always has been, a questionable
thing to do - for several reasons.
First, it's expensive. Pages need to be identified, locked and isolated
from various MM operations, and reassigned, one by one.
Second, it's unreliable. Once pages are charged to a cgroup, there isn't
always a clear owner task anymore. Cache isn't moved at all, for example.
Mapped memory is moved - but if trylocking or isolating a page fails,
it's arbitrarily left behind. Frequent moving between domains may leave a
task's memory scattered all over the place.
Third, it isn't really needed. Launcher tasks can kick off workload tasks
directly in their target cgroup. Using dedicated per-workload groups
allows fine-grained policy adjustments - no need to move tasks and their
physical pages between control domains. The feature was never
forward-ported to cgroup2, and it hasn't been missed.
Despite it being a niche usecase, the maintenance overhead of supporting
it is enormous. Because pages are moved while they are live and subject
to various MM operations, the synchronization rules are complicated.
There are lock_page_memcg() in MM and FS code, which non-cgroup people
don't understand. In some cases we've been able to shift code and cgroup
API calls around such that we can rely on native locking as much as
possible. But that's fragile, and sometimes we need to hold MM locks for
longer than we otherwise would (pte lock e.g.).
Mark the feature deprecated. Hopefully we can remove it soon.
And backport into -stable kernels so that people who develop against
earlier kernels are warned about this deprecation as early as possible.
[akpm@linux-foundation.org: fix memory.rst underlining]
Link: https://lkml.kernel.org/r/Y5COd+qXwk/S+n8N@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Pull cgroup updates from Tejun Heo:
- Christian extended clone3 so that processes can be spawned into
cgroups directly.
This is not only neat in terms of semantics but also avoids grabbing
the global cgroup_threadgroup_rwsem for migration.
- Daniel added !root xattr support to cgroupfs.
Userland already uses xattrs on cgroupfs for bookkeeping. This will
allow delegated cgroups to support such usages.
- Prateek tried to make cpuset hotplug handling synchronous but that
led to possible deadlock scenarios. Reverted.
- Other minor changes including release_agent_path handling cleanup.
* 'for-5.7' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
docs: cgroup-v1: Document the cpuset_v2_mode mount option
Revert "cpuset: Make cpuset hotplug synchronous"
cgroupfs: Support user xattrs
kernfs: Add option to enable user xattrs
kernfs: Add removed_size out param for simple_xattr_set
kernfs: kvmalloc xattr value instead of kmalloc
cgroup: Restructure release_agent_path handling
selftests/cgroup: add tests for cloning into cgroups
clone3: allow spawning processes into cgroups
cgroup: add cgroup_may_write() helper
cgroup: refactor fork helpers
cgroup: add cgroup_get_from_file() helper
cgroup: unify attach permission checking
cpuset: Make cpuset hotplug synchronous
cgroup.c: Use built-in RCU list checking
kselftest/cgroup: add cgroup destruction test
cgroup: Clean up css_set task traversal
The cpuset in cgroup v1 accepts a special "cpuset_v2_mode" mount
option that make cpuset.cpus and cpuset.mems behave more like those in
cgroup v2. Document it to make other people more aware of this feature
that can be useful in some circumstances.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cgroup v1 memcg controller has exposed a dedicated kmem limit to users
which turned out to be really a bad idea because there are paths which
cannot shrink the kernel memory usage enough to get below the limit (e.g.
because the accounted memory is not reclaimable). There are cases when
the failure is even not allowed (e.g. __GFP_NOFAIL). This means that the
kmem limit is in excess to the hard limit without any way to shrink and
thus completely useless. OOM killer cannot be invoked to handle the
situation because that would lead to a premature oom killing.
As a result many places might see ENOMEM returning from kmalloc and result
in unexpected errors. E.g. a global OOM killer when there is a lot of
free memory because ENOMEM is translated into VM_FAULT_OOM in #PF path and
therefore pagefault_out_of_memory would result in OOM killer.
Please note that the kernel memory is still accounted to the overall limit
along with the user memory so removing the kmem specific limit should
still allow to contain kernel memory consumption. Unlike the kmem one,
though, it invokes memory reclaim and targeted memcg oom killing if
necessary.
Start the deprecation process by crying to the kernel log. Let's see
whether there are relevant usecases and simply return to EINVAL in the
second stage if nobody complains in few releases.
[akpm@linux-foundation.org: tweak documentation text]
Link: http://lkml.kernel.org/r/20190911151612.GI4023@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Thomas Lindroth <thomas.lindroth@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
changeset fb5772cbfe ("blkio-controller.txt: Remove references to CFQ")
removed cgroup references to CFQ, but it kept one left. Get rid of
it.
Fixes: fb5772cbfe ("blkio-controller.txt: Remove references to CFQ")
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
