mm: change per-VMA lock statistics to be disabled by default

Change CONFIG_PER_VMA_LOCK_STATS to be disabled by default, as most users
don't need it.  Add configuration help to clarify its usage.

Link: https://lkml.kernel.org/r/20230428173533.18158-1-surenb@google.com
Fixes: 52f238653e45 ("mm: introduce per-VMA lock statistics")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 6dae63b..a925415 100644 (file)
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -274,6 +274,12 @@ config DEBUG_KMEMLEAK_AUTO_SCAN
 config PER_VMA_LOCK_STATS
        bool "Statistics for per-vma locks"
        depends on PER_VMA_LOCK
-       default y
        help
-         Statistics for per-vma locks.
+         Say Y here to enable success, retry and failure counters of page
+         faults handled under protection of per-vma locks. When enabled, the
+         counters are exposed in /proc/vmstat. This information is useful for
+         kernel developers to evaluate effectiveness of per-vma locks and to
+         identify pathological cases. Counting these events introduces a small
+         overhead in the page fault path.
+
+         If in doubt, say N.