* Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> [250509 08:14]:
> 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.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
I have a few tests for the vma test suite that would test this path.
I'll just let them go.
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> mm/vma.c | 14 --------------
> 1 file changed, 14 deletions(-)
>
> diff --git a/mm/vma.c b/mm/vma.c
> index 3f32e04bb6cc..3ff6cfbe3338 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;
> --
> 2.49.0
>
