mm: delete unused MMF_OOM_VICTIM flag

With the last usage of MMF_OOM_VICTIM in exit_mmap gone, this flag is now
unused and can be removed.

[[e-mail]: remove comment about now-removed mm_is_oom_victim()]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Suren Baghdasaryan <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: "Kirill A . Shutemov" <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Christian Brauner (Microsoft) <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Jann Horn <[e-mail]>
Cc: Shakeel Butt <[e-mail]>
Cc: Peter Xu <[e-mail]>
Cc: John Hubbard <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Liam Howlett <[e-mail]>

Signed-off-by: Andrew Morton <[e-mail]>

include/linux/oom.h

···
 }
 
 /*
- * Use this helper if tsk->mm != mm and the victim mm needs a special
- * handling. This is guaranteed to stay true after once set.
- */
-static inline bool mm_is_oom_victim(struct mm_struct *mm)
-{
-	return test_bit(MMF_OOM_VICTIM, &mm->flags);
-}
-
-/*
  * Checks whether a page fault on the given mm is still reliable.
  * This is no longer true if the oom reaper started to reap the
  * address space which is reflected by MMF_UNSTABLE flag set in

include/linux/sched/coredump.h

···
 #define MMF_UNSTABLE		22	/* mm is unstable for copy_from_user */
 #define MMF_HUGE_ZERO_PAGE	23      /* mm has ever used the global huge zero page */
 #define MMF_DISABLE_THP		24	/* disable THP for all VMAs */
-#define MMF_OOM_VICTIM		25	/* mm is the oom victim */
-#define MMF_OOM_REAP_QUEUED	26	/* mm was queued for oom_reaper */
-#define MMF_MULTIPROCESS	27	/* mm is shared between processes */
+#define MMF_OOM_REAP_QUEUED	25	/* mm was queued for oom_reaper */
+#define MMF_MULTIPROCESS	26	/* mm is shared between processes */
 /*
  * MMF_HAS_PINNED: Whether this mm has pinned any pages.  This can be either
  * replaced in the future by mm.pinned_vm when it becomes stable, or grow into
···
  * pinned pages were unpinned later on, we'll still keep this bit set for the
  * lifecycle of this mm, just for simplicity.
  */
-#define MMF_HAS_PINNED		28	/* FOLL_PIN has run, never cleared */
+#define MMF_HAS_PINNED		27	/* FOLL_PIN has run, never cleared */
 #define MMF_DISABLE_THP_MASK	(1 << MMF_DISABLE_THP)
 
 #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\

mm/mmap.c

···
 
 	/*
 	 * Set MMF_OOM_SKIP to hide this task from the oom killer/reaper
-	 * because the memory has been already freed. Do not bother checking
-	 * mm_is_oom_victim because setting a bit unconditionally is cheaper.
+	 * because the memory has been already freed.
 	 */
 	set_bit(MMF_OOM_SKIP, &mm->flags);
 	mmap_write_lock(mm);

mm/oom_kill.c

···
 		return;
 
 	/* oom_mm is bound to the signal struct life time. */
-	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
+	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
 		mmgrab(tsk->signal->oom_mm);
-		set_bit(MMF_OOM_VICTIM, &mm->flags);
-	}
 
 	/*
 	 * Make sure that the task is woken up from uninterruptible sleep