From 4cac0fd3128893fb42de3abba334376b829b825c Mon Sep 17 00:00:00 2001 From: "Lorenzo Stoakes (ARM)" Date: Thu, 3 Sep 2026 20:08:39 +0100 Subject: [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED 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 Closes: https://lore.kernel.org/all/CABeknB_S2XJSHFgnHdgnN0rjzHhH4oQJs_APq9fvxHztQ_pgiA@mail.gmail.com/ Signed-off-by: Lorenzo Stoakes (ARM) Signed-off-by: Andrew Morton Acked-by: Vlastimil Babka (SUSE) Reviewed-by: Pedro Falcato Cc: David Hildenbrand Cc: Jann Horn Cc: Liam R. Howlett --- mm/madvise.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index 73c2901b9adb..963337f93a7a 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -297,11 +297,12 @@ static long madvise_willneed(struct madvise_behavior *madv_behavior) 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);