Re: [PATCH v6 3/3] drm/buddy: Add defragmentation support

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 16.02.24 um 14:21 schrieb Matthew Auld:
> On 16/02/2024 12:33, Christian König wrote:
>> Am 16.02.24 um 13:23 schrieb Matthew Auld:
>>> On 08/02/2024 15:50, Arunpravin Paneer Selvam wrote:
>>>> Add a function to support defragmentation.
>>>>
>>>> v1: Defragment the memory beginning from min_order
>>>>      till the required memory space is available.
>>>>
>>>> Signed-off-by: Arunpravin Paneer Selvam 
>>>> <Arunpravin.PaneerSelvam@amd.com>
>>>> Suggested-by: Matthew Auld <matthew.auld@intel.com>
>>>> ---
>>>>   drivers/gpu/drm/drm_buddy.c | 67 
>>>> +++++++++++++++++++++++++++++++------
>>>>   include/drm/drm_buddy.h     |  3 ++
>>>
>>> No users?
>>
>> Other question is how can a buddy allocator fragment in the first place?
>
> The fragmentation is due to pages now being tracked as dirty/clear. 
> Should the allocator merge together a page that is dirty with a page 
> that is cleared? When should it do that? User wants to be able to keep 
> the two separate if possible. For example, freeing one single dirty 
> page can dirty a huge swathe of your already cleared pages if they are 
> merged together. Or do you have some some other ideas here?

Sorry, that was not what I meant. I should probably have been clearer.

That dirty and clean pages are now kept separated is obvious, but why do 
you need to de-fragment them at some point?

Christian.

>
>>
>> Christian.
>>
>>>
>>>>   2 files changed, 59 insertions(+), 11 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
>>>> index 33ad0cfbd54c..fac423d2cb73 100644
>>>> --- a/drivers/gpu/drm/drm_buddy.c
>>>> +++ b/drivers/gpu/drm/drm_buddy.c
>>>> @@ -276,10 +276,12 @@ drm_get_buddy(struct drm_buddy_block *block)
>>>>   }
>>>>   EXPORT_SYMBOL(drm_get_buddy);
>>>>   -static void __drm_buddy_free(struct drm_buddy *mm,
>>>> -                 struct drm_buddy_block *block)
>>>> +static unsigned int __drm_buddy_free(struct drm_buddy *mm,
>>>> +                     struct drm_buddy_block *block,
>>>> +                     bool defrag)
>>>>   {
>>>>       struct drm_buddy_block *parent;
>>>> +    unsigned int order;
>>>>         while ((parent = block->parent)) {
>>>>           struct drm_buddy_block *buddy;
>>>> @@ -289,12 +291,14 @@ static void __drm_buddy_free(struct drm_buddy 
>>>> *mm,
>>>>           if (!drm_buddy_block_is_free(buddy))
>>>>               break;
>>>>   -        if (drm_buddy_block_is_clear(block) !=
>>>> -            drm_buddy_block_is_clear(buddy))
>>>> -            break;
>>>> +        if (!defrag) {
>>>> +            if (drm_buddy_block_is_clear(block) !=
>>>> +                drm_buddy_block_is_clear(buddy))
>>>> +                break;
>>>>   -        if (drm_buddy_block_is_clear(block))
>>>> -            mark_cleared(parent);
>>>> +            if (drm_buddy_block_is_clear(block))
>>>> +                mark_cleared(parent);
>>>> +        }
>>>
>>> Maybe check if the two blocks are incompatible and chuck a warn if 
>>> they are not? Main thing is not to hide issues with split blocks 
>>> that should have been merged before.
>>>
>>>> list_del(&buddy->link);
>>>>   @@ -304,8 +308,49 @@ static void __drm_buddy_free(struct 
>>>> drm_buddy *mm,
>>>>           block = parent;
>>>>       }
>>>>   +    order = drm_buddy_block_order(block);
>>>>       mark_free(mm, block);
>>>> +
>>>> +    return order;
>>>> +}
>>>> +
>>>> +/**
>>>> + * drm_buddy_defrag - Defragmentation routine
>>>> + *
>>>> + * @mm: DRM buddy manager
>>>> + * @min_order: minimum order in the freelist to begin
>>>> + * the defragmentation process
>>>> + *
>>>> + * Driver calls the defragmentation function when the
>>>> + * requested memory allocation returns -ENOSPC.
>>>> + */
>>>> +void drm_buddy_defrag(struct drm_buddy *mm,
>>>> +              unsigned int min_order)
>>>
>>> Just wondering if we need "full defag" also? We would probably need 
>>> to call this at fini() anyway.
>>>
>>>> +{
>>>> +    struct drm_buddy_block *block;
>>>> +    struct list_head *list;
>>>> +    unsigned int order;
>>>> +    int i;
>>>> +
>>>> +    if (min_order > mm->max_order)
>>>> +        return;
>>>> +
>>>> +    for (i = min_order - 1; i >= 0; i--) {
>>>
>>> Need to be careful with min_order = 0 ?
>>>
>>>> +        list = &mm->free_list[i];
>>>> +        if (list_empty(list))
>>>> +            continue;
>>>> +
>>>> +        list_for_each_entry_reverse(block, list, link) {
>>>
>>> Don't we need the safe_reverse() variant here, since this is 
>>> removing from the list?
>>>
>>>> +            if (!block->parent)
>>>> +                continue;
>>>> +
>>>> +            order = __drm_buddy_free(mm, block, 1);
>>>> +            if (order >= min_order)
>>>> +                return;
>>>> +        }
>>>> +    }
>>>>   }
>>>> +EXPORT_SYMBOL(drm_buddy_defrag);
>>>>     /**
>>>>    * drm_buddy_free_block - free a block
>>>> @@ -321,7 +366,7 @@ void drm_buddy_free_block(struct drm_buddy *mm,
>>>>       if (drm_buddy_block_is_clear(block))
>>>>           mm->clear_avail += drm_buddy_block_size(mm, block);
>>>>   -    __drm_buddy_free(mm, block);
>>>> +    __drm_buddy_free(mm, block, 0);
>>>>   }
>>>>   EXPORT_SYMBOL(drm_buddy_free_block);
>>>>   @@ -470,7 +515,7 @@ __alloc_range_bias(struct drm_buddy *mm,
>>>>       if (buddy &&
>>>>           (drm_buddy_block_is_free(block) &&
>>>>            drm_buddy_block_is_free(buddy)))
>>>> -        __drm_buddy_free(mm, block);
>>>> +        __drm_buddy_free(mm, block, 0);
>>>>       return ERR_PTR(err);
>>>>   }
>>>>   @@ -588,7 +633,7 @@ alloc_from_freelist(struct drm_buddy *mm,
>>>>     err_undo:
>>>>       if (tmp != order)
>>>> -        __drm_buddy_free(mm, block);
>>>> +        __drm_buddy_free(mm, block, 0);
>>>>       return ERR_PTR(err);
>>>>   }
>>>>   @@ -668,7 +713,7 @@ static int __alloc_range(struct drm_buddy *mm,
>>>>       if (buddy &&
>>>>           (drm_buddy_block_is_free(block) &&
>>>>            drm_buddy_block_is_free(buddy)))
>>>> -        __drm_buddy_free(mm, block);
>>>> +        __drm_buddy_free(mm, block, 0);
>>>>     err_free:
>>>>       if (err == -ENOSPC && total_allocated_on_err) {
>>>> diff --git a/include/drm/drm_buddy.h b/include/drm/drm_buddy.h
>>>> index d81c596dfa38..d0f63e7b5915 100644
>>>> --- a/include/drm/drm_buddy.h
>>>> +++ b/include/drm/drm_buddy.h
>>>> @@ -166,6 +166,9 @@ void drm_buddy_free_list(struct drm_buddy *mm,
>>>>                struct list_head *objects,
>>>>                unsigned int flags);
>>>>   +void drm_buddy_defrag(struct drm_buddy *mm,
>>>> +              unsigned int min_order);
>>>> +
>>>>   void drm_buddy_print(struct drm_buddy *mm, struct drm_printer *p);
>>>>   void drm_buddy_block_print(struct drm_buddy *mm,
>>>>                  struct drm_buddy_block *block,
>>