From bf3480d7d0bce40d8687559fd6ff40c233a7052f Mon Sep 17 00:00:00 2001 From: Weilin Tong Date: Mon, 15 Dec 2025 10:46:32 +0800 Subject: [PATCH] mm/shmem: add mTHP swpout fallback statistics in shmem_writeout() Currently, when shmem mTHPs are split and swapped out via shmem_writeout(), there are no unified statistics to trace these mTHP swpout fallback events. This makes it difficult to analyze the prevalence of mTHP splitting and fallback during swap operations, which is important for memory diagnostics. Here we add statistics counting for mTHP fallback to small pages when splitting and swapping out in shmem_writeout(). Link: https://lkml.kernel.org/r/20251215024632.250149-1-tongweilin@linux.alibaba.com Signed-off-by: Weilin Tong Reviewed-by: Baolin Wang Cc: Hugh Dickins Signed-off-by: Andrew Morton --- mm/shmem.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index ec6c01378e9d..15c2943140ca 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1593,11 +1593,23 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug, } if (split) { + int order; + try_split: + order = folio_order(folio); /* Ensure the subpages are still dirty */ folio_test_set_dirty(folio); if (split_folio_to_list(folio, folio_list)) goto redirty; + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + if (order >= HPAGE_PMD_ORDER) { + count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1); + count_vm_event(THP_SWPOUT_FALLBACK); + } +#endif + count_mthp_stat(order, MTHP_STAT_SWPOUT_FALLBACK); + folio_clear_dirty(folio); } -- 2.47.3