Re: [RFC PATCH 2/7] vm: Allow coalescing a VM object with itself

[Samuel Thibault]

Applied, thanks!

Sergey Bugaev, le lun. 26 juin 2023 14:26:51 +0300, a ecrit:
> If a mapping of an object is made right next to another mapping of the
> same object have the same properties (protection, inheritance, etc.),
> Mach will now expand the previous VM map entry to cover the new address
> range instead of creating a new entry.
> ---
>  vm/vm_map.c    | 12 ++++++------
>  vm/vm_object.c | 22 +++++++++++++++++-----
>  2 files changed, 23 insertions(+), 11 deletions(-)
> 
> diff --git a/vm/vm_map.c b/vm/vm_map.c
> index 186589a4..a41e6434 100644
> --- a/vm/vm_map.c
> +++ b/vm/vm_map.c
> @@ -1073,8 +1073,7 @@ kern_return_t vm_map_enter(
>        *      extend from below.]
>        */
>  
> -     if ((object == VM_OBJECT_NULL) &&
> -         (entry != vm_map_to_entry(map)) &&
> +     if ((entry != vm_map_to_entry(map)) &&
>           (entry->vme_end == start) &&
>           (!entry->is_shared) &&
>           (!entry->is_sub_map) &&
> @@ -1084,20 +1083,21 @@ kern_return_t vm_map_enter(
>           (entry->wired_count == 0) &&
>           (entry->projected_on == 0)) {
>               if (vm_object_coalesce(entry->object.vm_object,
> -                             VM_OBJECT_NULL,
> +                             object,
>                               entry->offset,
> -                             (vm_offset_t) 0,
> +                             offset,
>                               (vm_size_t)(entry->vme_end - entry->vme_start),
> -                             (vm_size_t)(end - entry->vme_end))) {
> +                             size)) {
>  
>                       /*
>                        *      Coalesced the two objects - can extend
>                        *      the previous map entry to include the
>                        *      new range.
>                        */
> -                     map->size += (end - entry->vme_end);
> +                     map->size += size;
>                       entry->vme_end = end;
>                       vm_map_gap_update(&map->hdr, entry);
> +                     vm_object_deallocate(object);
>                       RETURN(KERN_SUCCESS);
>               }
>       }
> diff --git a/vm/vm_object.c b/vm/vm_object.c
> index b5be3f81..b00e90d2 100644
> --- a/vm/vm_object.c
> +++ b/vm/vm_object.c
> @@ -2693,7 +2693,8 @@ void vm_object_page_remove(
>   *   returns TRUE if objects were combined.
>   *
>   *   NOTE:   Only works at the moment if the second object is NULL -
> - *           if it's not, which object do we lock first?
> + *           or if the objects are the same - otherwise, which
> + *           object do we lock first?
>   *
>   *   Parameters:
>   *           prev_object     First object to coalesce
> @@ -2718,12 +2719,23 @@ boolean_t vm_object_coalesce(
>  {
>       vm_size_t       newsize;
>  
> -     if (next_object != VM_OBJECT_NULL) {
> -             return FALSE;
> +     if (prev_object == next_object) {
> +             /*
> +              *      If neither object actually exists,
> +              *      the offsets don't matter.
> +              */
> +             if (prev_object == VM_OBJECT_NULL)
> +                     return TRUE;
> +
> +             return prev_offset + prev_size == next_offset;
>       }
>  
> -     if (prev_object == VM_OBJECT_NULL) {
> -             return TRUE;
> +     if (next_object != VM_OBJECT_NULL) {
> +             /*
> +              *      Don't know how to merge two different
> +              *      objects yet.
> +              */
> +             return FALSE;
>       }
>  
>       vm_object_lock(prev_object);
> -- 
> 2.41.0
> 

-- 
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.