mm/zswap: stop lru list shrinking when encounter warm region

When the shrinker encounter an existing folio in swap cache, it means we
are shrinking into the warmer region.  We should terminate shrinking if
we're in the dynamic shrinker context.

This patch add LRU_STOP to support this, to avoid overshrinking.

Link: https://lkml.kernel.org/r/20240201-b4-zswap-invalidate-entry-v2-3-99d4084260a0@bytedance.com
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index f2882a8..792b67c 100644 (file)
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -24,6 +24,8 @@ enum lru_status {
        LRU_SKIP,               /* item cannot be locked, skip */
        LRU_RETRY,              /* item not freeable. May drop the lock
                                   internally, but has to return locked. */
+       LRU_STOP,               /* stop lru list walking. May drop the lock
+                                  internally, but has to return locked. */
 };
 
 struct list_lru_one {

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 61f3b6b..3fd6473 100644 (file)
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -243,6 +243,9 @@ restart:
                         */
                        assert_spin_locked(&nlru->lock);
                        goto restart;
+               case LRU_STOP:
+                       assert_spin_locked(&nlru->lock);
+                       goto out;
                default:
                        BUG();
                }

diff --git a/mm/zswap.c b/mm/zswap.c
index ef41a7b..f8a4ac3 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1315,8 +1315,10 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
                 * into the warmer region. We should terminate shrinking (if we're in the dynamic
                 * shrinker context).
                 */
-               if (writeback_result == -EEXIST && encountered_page_in_swapcache)
+               if (writeback_result == -EEXIST && encountered_page_in_swapcache) {
+                       ret = LRU_STOP;
                        *encountered_page_in_swapcache = true;
+               }
        } else {
                zswap_written_back_pages++;
        }