[PATCH v2 03/26] mm/fbatch: temporarily disable lazyfree and mlock+munlock batching

[Hugh Dickins <hughd@google.com>]

It will not matter if we occasionally get activation or deactivation
wrong; but a mistaken lazyfree (MADV_FREE) would likely cause dataloss.
So disable its batching while reworking the per-cpu fbatch handling,
then re-enable it with more thought afterwards.

Similarly disable mlock+munlock batching temporarily: they will need
some redesign before re-enabling. Just insert one disabling line for
now, leaving the rest of the code as it was, for consideration later.

Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-By: Vlastimil Babka (SUSE) <vbabka@kernel.org>
---
 mm/folio.c | 2 ++
 mm/mlock.c | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/mm/folio.c b/mm/folio.c
index ad6c64a4c22c..b9dc4f5e10a6 100644
--- a/mm/folio.c
+++ b/mm/folio.c
@@ -219,6 +219,8 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch,
 		local_lock(&cpu_fbatches.lock);
 
 	if (!folio_batch_add(this_cpu_ptr(fbatch), folio) ||
+			/* XXX Temporarily disable lazyfree batching */
+			fbatch == &cpu_fbatches.lru_lazyfree ||
 			!folio_may_be_lru_cached(folio) || lru_cache_disabled())
 		folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn);
 
diff --git a/mm/mlock.c b/mm/mlock.c
index 39215a3eab1f..929abeac85d0 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -255,6 +255,7 @@ void mlock_folio(struct folio *folio)
 
 	folio_get(folio);
 	if (!folio_batch_add(fbatch, mlock_lru(folio)) ||
+	    true || /* XXX Temporarily disable mlock batching */
 	    !folio_may_be_lru_cached(folio) || lru_cache_disabled())
 		mlock_folio_batch(fbatch);
 	local_unlock(&mlock_fbatch.lock);
@@ -278,6 +279,7 @@ void mlock_new_folio(struct folio *folio)
 
 	folio_get(folio);
 	if (!folio_batch_add(fbatch, mlock_new(folio)) ||
+	    true || /* XXX Temporarily disable mlock_new batching */
 	    !folio_may_be_lru_cached(folio) || lru_cache_disabled())
 		mlock_folio_batch(fbatch);
 	local_unlock(&mlock_fbatch.lock);
@@ -299,6 +301,7 @@ void munlock_folio(struct folio *folio)
 	 */
 	folio_get(folio);
 	if (!folio_batch_add(fbatch, folio) ||
+	    true || /* XXX Temporarily disable munlock batching */
 	    !folio_may_be_lru_cached(folio) || lru_cache_disabled())
 		mlock_folio_batch(fbatch);
 	local_unlock(&mlock_fbatch.lock);
-- 
2.51.0