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/[email protected]
Fixes: 52f238653e45 ("mm: introduce per-VMA lock statistics")
Signed-off-by: Suren Baghdasaryan <[email protected]>
Suggested-by: Linus Torvalds <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 6dae63b4636823cb6ad6f9c068dec3f6e99d8aaa..a925415b4d1097661fd4d2425c513c5526bce164 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.