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Cgroup has a standardized poll/notification mechanism for waking all pollers on all fds when a filesystem node changes. To allow polling for custom events, add a .poll callback that can override the default. This is in preparation for pollable cgroup pressure files which have per-fd trigger configurations. Link: http://lkml.kernel.org/r/20190124211518.244221-3-surenb@google.com Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Suren Baghdasaryan <surenb@google.com> Cc: Dennis Zhou <dennis@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Li Zefan <lizefan@huawei.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au> (cherry picked from commit: dc50537bdd1a0804fa2cbc990565ee9a944e66fa) Conflicts: include/linux/cgroup-defs.h kernel/cgroup.c (1. replaced __poll_t with unsigned int) Bug: 127712811 Test: lmkd in PSI mode Change-Id: I21aff1d9d31e3d4b45e257aa4d299405a2ce6de3 Signed-off-by: Suren Baghdasaryan <surenb@google.com>