[PATCH v4 4/6] drm: implement a method to free unused pages
Arunpravin
arunpravin.paneerselvam at amd.com
Wed Dec 15 20:56:36 UTC 2021
On 14/12/21 12:10 am, Matthew Auld wrote:
> On 01/12/2021 16:39, Arunpravin wrote:
>> On contiguous allocation, we round up the size
>> to the *next* power of 2, implement a function
>> to free the unused pages after the newly allocate block.
>>
>> v2(Matthew Auld):
>> - replace function name 'drm_buddy_free_unused_pages' with
>> drm_buddy_block_trim
>> - replace input argument name 'actual_size' with 'new_size'
>> - add more validation checks for input arguments
>> - add overlaps check to avoid needless searching and splitting
>> - merged the below patch to see the feature in action
>> - add free unused pages support to i915 driver
>> - lock drm_buddy_block_trim() function as it calls mark_free/mark_split
>> are all globally visible
>>
>> v3:
>> - remove drm_buddy_block_trim() error handling and
>> print a warn message if it fails
>>
>> Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam at amd.com>
>> ---
>> drivers/gpu/drm/drm_buddy.c | 72 ++++++++++++++++++-
>> drivers/gpu/drm/i915/i915_ttm_buddy_manager.c | 10 +++
>> include/drm/drm_buddy.h | 4 ++
>> 3 files changed, 83 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
>> index eddc1eeda02e..707efc82216d 100644
>> --- a/drivers/gpu/drm/drm_buddy.c
>> +++ b/drivers/gpu/drm/drm_buddy.c
>> @@ -434,7 +434,8 @@ alloc_from_freelist(struct drm_buddy_mm *mm,
>> static int __alloc_range(struct drm_buddy_mm *mm,
>> struct list_head *dfs,
>> u64 start, u64 size,
>> - struct list_head *blocks)
>> + struct list_head *blocks,
>> + bool trim_path)
>> {
>> struct drm_buddy_block *block;
>> struct drm_buddy_block *buddy;
>> @@ -480,8 +481,20 @@ static int __alloc_range(struct drm_buddy_mm *mm,
>>
>> if (!drm_buddy_block_is_split(block)) {
>> err = split_block(mm, block);
>> - if (unlikely(err))
>> + if (unlikely(err)) {
>> + if (trim_path)
>> + /*
>> + * Here in case of trim, we return and dont goto
>> + * split failure path as it removes from the
>> + * original list and potentially also freeing
>> + * the block. so we could leave as it is,
>> + * worse case we get some internal fragmentation
>> + * and leave the decision to the user
>> + */
>> + return err;
>
> Hmm, ideally we don't want to leave around blocks where both buddies are
> free without then also merging them back(not sure if that trips some
> BUG_ON). Also IIUC, if we hit this failure path, depending on where the
> split_block() fails we might be allocating something less than new_size?
> Also if it's the first split_block() that fails then the user just gets
> an empty list?
>
> Could we perhaps just turn this node into a temporary root node to
> prevent recursively freeing itself, but still retain the
> un-splitting/freeing of the other nodes i.e something like:
>
> list_del(&block->link);
> mark_free(mm, block);
> mm->avail += ...;
>
> /* Prevent recursively freeing this node */
> parent = block->parent;
> block->parent = NULL;
>
> list_add(&block->tmp_link, &dfs);
> ret = _alloc_range(mm, &dfs, new_start, new_size, blocks);
> if (ret) {
> mem->avail -= ...;
> mark_allocated(block);
> list_add(&block->link, blocks);
> }
>
> block->parent = parent;
> return ret;
>
> That way we can also drop the special trim_path handling. Thoughts?
That's a nice idea. It will work.
>
>> +
>> goto err_undo;
>> + }
>> }
>>
>> list_add(&block->right->tmp_link, dfs);
>> @@ -535,8 +548,61 @@ static int __drm_buddy_alloc_range(struct drm_buddy_mm *mm,
>> for (i = 0; i < mm->n_roots; ++i)
>> list_add_tail(&mm->roots[i]->tmp_link, &dfs);
>>
>> - return __alloc_range(mm, &dfs, start, size, blocks);
>> + return __alloc_range(mm, &dfs, start, size, blocks, 0);
>> +}
>> +
>> +/**
>> + * drm_buddy_block_trim - free unused pages
>> + *
>> + * @mm: DRM buddy manager
>> + * @new_size: original size requested
>> + * @blocks: output list head to add allocated blocks
>> + *
>> + * For contiguous allocation, we round up the size to the nearest
>> + * power of two value, drivers consume *actual* size, so remaining
>> + * portions are unused and it can be freed.
>> + *
>> + * Returns:
>> + * 0 on success, error code on failure.
>> + */
>> +int drm_buddy_block_trim(struct drm_buddy_mm *mm,
>> + u64 new_size,
>> + struct list_head *blocks)
>> +{
>> + struct drm_buddy_block *block;
>> + u64 new_start;
>> + LIST_HEAD(dfs);
>> +
>> + if (!list_is_singular(blocks))
>> + return -EINVAL;
>> +
>> + block = list_first_entry(blocks,
>> + struct drm_buddy_block,
>> + link);
>> +
>> + if (!drm_buddy_block_is_allocated(block))
>> + return -EINVAL;
>> +
>> + if (new_size > drm_buddy_block_size(mm, block))
>> + return -EINVAL;
>> +
>> + if (!new_size && !IS_ALIGNED(new_size, mm->chunk_size))
>> + return -EINVAL;
>> +
>> + if (new_size == drm_buddy_block_size(mm, block))
>> + return 0;
>> +
>> + list_del(&block->link);
>> +
>> + new_start = drm_buddy_block_offset(block);
>> +
>> + mark_free(mm, block);
>> +
>> + list_add(&block->tmp_link, &dfs);
>> +
>> + return __alloc_range(mm, &dfs, new_start, new_size, blocks, 1);
>> }
>> +EXPORT_SYMBOL(drm_buddy_block_trim);
>>
>> /**
>> * drm_buddy_alloc - allocate power-of-two blocks
>> diff --git a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
>> index 7c58efb60dba..c5831c27fe82 100644
>> --- a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
>> +++ b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
>> @@ -97,6 +97,16 @@ static int i915_ttm_buddy_man_alloc(struct ttm_resource_manager *man,
>> if (unlikely(err))
>> goto err_free_blocks;
>>
>> + if (place->flags & TTM_PL_FLAG_CONTIGUOUS) {
>> + mutex_lock(&bman->lock);
>> + err = drm_buddy_block_trim(mm,
>> + (u64)n_pages << PAGE_SHIFT,
>> + &bman_res->blocks);
>> + mutex_unlock(&bman->lock);
>> + pr_warn("drm_buddy_block_trim failed returing %d for ttm_buffer_object(%p)\n",
>> + err, bo);
>
>
> IIUC this prints a warning even for success? Anyway, I think we can drop
> the pr_warn, since normal user can't really do much here?
Yes, I will drop pr_warn
>
>> + }
>> +
>> *res = &bman_res->base;
>> return 0;
>>
>> diff --git a/include/drm/drm_buddy.h b/include/drm/drm_buddy.h
>> index 316ac0d25f08..90906d9dbbf0 100644
>> --- a/include/drm/drm_buddy.h
>> +++ b/include/drm/drm_buddy.h
>> @@ -146,6 +146,10 @@ int drm_buddy_alloc(struct drm_buddy_mm *mm,
>> struct list_head *blocks,
>> unsigned long flags);
>>
>> +int drm_buddy_block_trim(struct drm_buddy_mm *mm,
>> + u64 new_size,
>> + struct list_head *blocks);
>> +
>> void drm_buddy_free(struct drm_buddy_mm *mm, struct drm_buddy_block *block);
>>
>> void drm_buddy_free_list(struct drm_buddy_mm *mm, struct list_head *objects);
>>
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