+ mm-shmem-add-mthp-swpout-fallback-statistics-in-shmem_writeout.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/shmem: add mTHP swpout fallback statistics in shmem_writeout()
has been added to the -mm mm-new branch.  Its filename is
     mm-shmem-add-mthp-swpout-fallback-statistics-in-shmem_writeout.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-add-mthp-swpout-fallback-statistics-in-shmem_writeout.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Weilin Tong <tongweilin@linux.alibaba.com>
Subject: mm/shmem: add mTHP swpout fallback statistics in shmem_writeout()
Date: Mon, 15 Dec 2025 10:46:32 +0800

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 <tongweilin@linux.alibaba.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/mm/shmem.c~mm-shmem-add-mthp-swpout-fallback-statistics-in-shmem_writeout
+++ a/mm/shmem.c
@@ -1593,11 +1593,23 @@ int shmem_writeout(struct folio *folio,
 	}
 
 	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);
 	}
 
_

Patches currently in -mm which might be from tongweilin@linux.alibaba.com are

mm-shmem-add-mthp-swpout-fallback-statistics-in-shmem_writeout.patch