On 18/11/21 12:32 am, Matthew Auld wrote:
> On 16/11/2021 20:18, 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
>>
>> Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam@xxxxxxx>
>> ---
>> drivers/gpu/drm/drm_buddy.c | 108 ++++++++++++++++++
>> drivers/gpu/drm/i915/i915_ttm_buddy_manager.c | 10 ++
>> include/drm/drm_buddy.h | 4 +
>> 3 files changed, 122 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
>> index 0a9db2981188..943fe2ad27bf 100644
>> --- a/drivers/gpu/drm/drm_buddy.c
>> +++ b/drivers/gpu/drm/drm_buddy.c
>> @@ -284,6 +284,114 @@ static inline bool contains(u64 s1, u64 e1, u64 s2, u64 e2)
>> return s1 <= s2 && e1 >= e2;
>> }
>>
>> +/**
>> + * 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;
>> + struct drm_buddy_block *buddy;
>> + u64 new_start;
>> + u64 new_end;
>> + LIST_HEAD(dfs);
>> + u64 count = 0;
>> + int err;
>> +
>> + 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);
>> + new_end = new_start + new_size - 1;
>> +
>> + mark_free(mm, block);
>> +
>> + list_add(&block->tmp_link, &dfs);
>> +
>> + do {
>> + u64 block_start;
>> + u64 block_end;
>> +
>> + block = list_first_entry_or_null(&dfs,
>> + struct drm_buddy_block,
>> + tmp_link);
>> + if (!block)
>> + break;
>> +
>> + list_del(&block->tmp_link);
>> +
>> + if (count == new_size)
>> + return 0;
>> +
>> + block_start = drm_buddy_block_offset(block);
>> + block_end = block_start + drm_buddy_block_size(mm, block) - 1;
>> +
>> + if (!overlaps(new_start, new_end, block_start, block_end))
>> + continue;
>> +
>> + if (contains(new_start, new_end, block_start, block_end)) {
>> + BUG_ON(!drm_buddy_block_is_free(block));
>> +
>> + /* Allocate only required blocks */
>> + mark_allocated(block);
>> + mm->avail -= drm_buddy_block_size(mm, block);
>> + list_add_tail(&block->link, blocks);
>> + count += drm_buddy_block_size(mm, block);
>> + continue;
>> + }
>> +
>> + if (!drm_buddy_block_is_split(block)) {
>
> Should always be true, right? But I guess depends if we want to re-use
> this for generic range allocation...
yes, since we re-use this for generic range allocation I think we can
keep this check
>
>> + err = split_block(mm, block);
>> + if (unlikely(err))
>> + goto err_undo;
>> + }
>> +
>> + list_add(&block->right->tmp_link, &dfs);
>> + list_add(&block->left->tmp_link, &dfs);
>> + } while (1);
>> +
>> + return -ENOSPC;
>> +
>> +err_undo:
>> + buddy = get_buddy(block);
>> + if (buddy &&
>> + (drm_buddy_block_is_free(block) &&
>> + drm_buddy_block_is_free(buddy)))
>> + __drm_buddy_free(mm, block);
>> + return err;
>
> Looking at the split_block failure path. The user allocated some block,
> and then tried to trim it, but this then marks it as free and removes it
> from their original list(potentially also freeing it), if we fail here.
> Would it be better to leave that decision to the user? If the trim()
> fails, worse case we get some internal fragmentation, and the user might
> be totally fine with that? I guess we could leave as-is, but for sure
> needs some big comment somewhere.
Agreed
would it make sense to add a bool type input argument, so that we can
skip the split_block failure path in case of block_trim().
__alloc_range(mm, &dfs, start, size, ... bool trim)
err = split_block(mm, block);
if (unlikely(err)) {
/* I think we can add big comment here for trim case */
if (trim)
return err;
goto err_undo;
}
>
>> +}
>> +EXPORT_SYMBOL(drm_buddy_block_trim);
>> +
>> static struct drm_buddy_block *
>> alloc_range(struct drm_buddy_mm *mm,
>> u64 start, u64 end,
>> diff --git a/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c b/drivers/gpu/drm/i915/i915_ttm_buddy_manager.c
>> index b6ed5b37cf18..5e1f8c443058 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);
>> + if (unlikely(err))
>> + goto err_free_blocks;
>
> Yeah, so maybe we could in theory treat this as best effort? But I guess
> unlikely to ever hit this anyway, so meh.
so I understood that we remove the below 2 lines
if (unlikely(err))
goto err_free_blocks;
would it make sense to print a WARN msg
WARN(err < 0, "Trim failed returning %d for ttm_resource(%llu)\n",
err, &bman_res->base);
>
>> + }
>> +
>> *res = &bman_res->base;
>> return 0;
>>
>> diff --git a/include/drm/drm_buddy.h b/include/drm/drm_buddy.h
>> index cbe5e648440a..36e8f548acf7 100644
>> --- a/include/drm/drm_buddy.h
>> +++ b/include/drm/drm_buddy.h
>> @@ -145,6 +145,10 @@ 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);
>>
