memcg, oom: remove explicit wakeup in mem_cgroup_oom_synchronize()

Before commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
charge path"), all memcg oom killers were delayed to page fault path.  And
the explicit wakeup is used in this case:

thread A:
        ...
        if (locked) {           // complete oom-kill, hold the lock
                mem_cgroup_oom_unlock(memcg);
                ...
        }
        ...

thread B:
        ...

        if (locked && !memcg->oom_kill_disable) {
                ...
        } else {
                schedule();     // can't acquire the lock
                ...
        }
        ...

The reason is that thread A kicks off the OOM-killer, which leads to
wakeups from the uncharges of the exiting task.  But thread B is not
guaranteed to see them if it enters the OOM path after the OOM kills but
before thread A releases the lock.

Now only oom_kill_disable case is handled from the #PF path.  In that case
it is userspace to trigger the wake up not the #PF path itself.  All
potential paths to free some charges are responsible to call
memcg_oom_recover() , so the explicit wakeup is not needed in the
mem_cgroup_oom_synchronize() path which doesn't release any memory itself.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Haifeng Xu <[email protected]>
Suggested-by: Michal Hocko <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Shakeel Butt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions