+ mm-madvise-swap-in-cowd-map_private-file-mappings-on-madv_willneed.patch added to mm-new branch

+ mm-madvise-swap-in-cowd-map_private-file-mappings-on-madv_willneed.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED
has been added to the -mm mm-new branch.  Its filename is
     mm-madvise-swap-in-cowd-map_private-file-mappings-on-madv_willneed.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-madvise-swap-in-cowd-map_private-file-mappings-on-madv_willneed.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED
Date: Thu, 3 Sep 2026 20:08:39 +0100

Currently MADV_WILLNEED treats file-backed and pure anonymous mappings
entirely separately - using POSIX_FADV_WILLNEED (equivalent of a
readahead) for the former and a tree walk and swap in to swap cache for
the latter.

MAP_PRIVATE-file backed mappings straddle the two and currently get
treated as if they were purely file-backed, meaning any swapped out
private pages remain swapped out.

Resolve the issue by explicitly checking for CoW'd MAP_PRIVATE-file backed
mappings and performing both walks in this case.

Since the logic checks for vma->anon_vma this means un-CoW'd
MAP_PRIVATE-file backed mappings retain only the single file walk.

Link: https://lore.kernel.org/aprjOxDy3JCPb2oa@gremlin
Reported-by: Mike Kaplinskiy <mike@recall.ai>
Closes: https://lore.kernel.org/all/CABeknB_S2XJSHFgnHdgnN0rjzHhH4oQJs_APq9fvxHztQ_pgiA@mail.gmail.com/
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/madvise.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/madvise.c~mm-madvise-swap-in-cowd-map_private-file-mappings-on-madv_willneed
+++ a/mm/madvise.c
@@ -297,11 +297,12 @@ static long madvise_willneed(struct madv
 	loff_t offset;
 
 #ifdef CONFIG_SWAP
-	if (!file) {
+	if (vma_is_cow_mapping(vma) && vma->anon_vma) {
 		walk_page_range_vma(vma, start, end, &swapin_walk_ops, vma);
 		lru_add_drain(); /* Push any new pages onto the LRU now */
-		return 0;
 	}
+	if (!file)
+		return 0;
 
 	if (shmem_mapping(file->f_mapping)) {
 		shmem_swapin_range(vma, start, end, file->f_mapping);
_

Patches currently in -mm which might be from ljs@kernel.org are

mm-vma-correctly-unaccount-on-mmap_prepare-failure.patch
mm-vmpressure-remove-window-size-todo.patch
tools-testing-selftests-mm-add-missing-gitignore-entries.patch
mm-move-drivers-char-memc-to-mm-char-memc.patch
mm-implement-file_is_dev_zero-to-uniquely-identify-dev-zero.patch
mm-vma-only-permit-map_private-dev-zero-to-be-mapped-anonymous.patch
mm-vma-make-map_private-mapped-dev-zero-mappings-truly-anonymous.patch
tools-testing-vma-add-test-to-assert-map_private-dev-zero-is-anon.patch
tools-testing-selftests-mm-add-map_private-dev-zero-merge-tests.patch
mm-madvise-swap-in-cowd-map_private-file-mappings-on-madv_willneed.patch