[RFC PATCH 0/3] mm: drop redundant lru_add_drain in anon folio reuse paths

["Barry Song (Xiaomi)" <baohua@kernel.org>]

We are doing a large number of redundant lru_add_drain() calls in
both wp_can_reuse_anon_folio() and do_swap_page(), leading to LRU
lock contention and unnecessary overhead.

In wp_can_reuse_anon_folio(), we can check the refcount against the
lru_cache before deciding to drain. In do_swap_page(), the drain is
now entirely redundant after Kairui's work to route SYNC I/O through
the swapcache in the same way as ASYNC I/O.

Build the kernel within a 1GB memcg using 20 threads with zRAM swap.
The number of lru_add_drain() calls is reduced from 276,787 to
230,283, while sys time decreases slightly from 3m40.125s to
3m37.128s.

Build the kernel within an 800MB memcg using 20 threads with zRAM
swap. The number of lru_add_drain() calls is reduced from 796,661 to
537,262, while sys time decreases slightly from 6m25.981s to
6m22.678s.

Barry Song (Xiaomi) (3):
  mm: avoid unnecessary lru drain for wp_can_reuse_anon_folio()
  mm: drop stale folio_ref_count()==1 check in do_swap_page reuse logic
  mm: entirely remove lru_add_drain in do_swap_page

 mm/memory.c | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

-- 
2.39.3 (Apple Git-146)