From 3c06ee7c24c27466c73209e00ee4c99e0115da1e Mon Sep 17 00:00:00 2001 From: Lorenzo Stoakes Date: Fri, 9 May 2025 13:13:36 +0100 Subject: [PATCH] mm/vma: remove mmap() retry merge We have now introduced a mechanism that obviates the need for a reattempted merge via the mmap_prepare() file hook, so eliminate this functionality altogether. The retry merge logic has been the cause of a great deal of complexity in the past and required a great deal of careful manoeuvring of code to ensure its continued and correct functionality. It has also recently been involved in an issue surrounding maple tree state, which again points to its problematic nature. We make it much easier to reason about mmap() logic by eliminating this and simply writing a VMA once. This also opens the doors to future optimisation and improvement in the mmap() logic. For any device or file system which encounters unwanted VMA fragmentation as a result of this change (that is, having not implemented .mmap_prepare hooks), the issue is easily resolvable by doing so. Link: https://lkml.kernel.org/r/d5d8fc74f02b89d6bec5ae8bc0e36d7853b65cda.1746792520.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes Reviewed-by: David Hildenbrand Reviewed-by: Vlastimil Babka Cc: Al Viro Cc: Christian Brauner Cc: Jan Kara Cc: Jann Horn Cc: Liam Howlett Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Rapoport (Microsoft) Cc: Suren Baghdasaryan Signed-off-by: Andrew Morton --- mm/vma.c | 14 -------------- 1 file changed, 14 deletions(-) diff --git a/mm/vma.c b/mm/vma.c index 3f32e04bb6cc3..3ff6cfbe33384 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -24,7 +24,6 @@ struct mmap_state { void *vm_private_data; unsigned long charged; - bool retry_merge; struct vm_area_struct *prev; struct vm_area_struct *next; @@ -2417,8 +2416,6 @@ static int __mmap_new_file_vma(struct mmap_state *map, !(map->flags & VM_MAYWRITE) && (vma->vm_flags & VM_MAYWRITE)); - /* If the flags change (and are mergeable), let's retry later. */ - map->retry_merge = vma->vm_flags != map->flags && !(vma->vm_flags & VM_SPECIAL); map->flags = vma->vm_flags; return 0; @@ -2622,17 +2619,6 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr, if (have_mmap_prepare) set_vma_user_defined_fields(vma, &map); - /* If flags changed, we might be able to merge, so try again. */ - if (map.retry_merge) { - struct vm_area_struct *merged; - VMG_MMAP_STATE(vmg, &map, vma); - - vma_iter_config(map.vmi, map.addr, map.end); - merged = vma_merge_existing_range(&vmg); - if (merged) - vma = merged; - } - __mmap_complete(&map, vma); return addr; -- 2.39.5