Please help review this patch. Thanks!
> From: "Zhaoyu Liu"<[email protected]> > Date: Thu, Jul 9, 2026, 19:20 > Subject: [PATCH] gpu: buddy: avoid repeated builds of root dfs when alloc > range > To: <[email protected]>, <[email protected]>, > <[email protected]>, <[email protected]>, <[email protected]> > Cc: <[email protected]>, <[email protected]> > The buddy allocator previously pre-built a DFS list by inserting all > root blocks via list_add_tail() before every allocation call in > __alloc_range_bias() and __gpu_buddy_alloc_range(). This is wasteful > when the allocation can be satisfied by the first root or by sub-blocks > produced from splits, as the remaining roots are never consumed. > > Introduce __get_candidate_block() which unifies the block acquisition > logic for both __alloc_range_bias() and __alloc_range(): it first > checks the DFS list (populated by splits during allocation or > pre-filled by the caller for trim), and only when the list is exhausted > does it lazily fetch the next root block through a cursor. > > When the caller pre-fills the DFS list (trim scenario), the cursor is > initialized to mm->n_roots to disable root iteration entirely, > preserving the original behavior. > > Signed-off-by: Zhaoyu Liu <[email protected]> > --- > drivers/gpu/buddy.c | 61 ++++++++++++++++++++++++++++++--------------- > 1 file changed, 41 insertions(+), 20 deletions(-) > > diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c > index dc81fe0301ce..2cebb87020c7 100644 > --- a/drivers/gpu/buddy.c > +++ b/drivers/gpu/buddy.c > @@ -700,6 +700,41 @@ static void __gpu_buddy_undo_splits(struct gpu_buddy *mm, > } > } > > +/** > + * __get_candidate_block - Get a candidate block for allocation. > + * @mm: GPU buddy manager > + * @dfs: List of candidate blocks. Populated in two ways: (1) pre-filled by > + * the caller before allocation with blocks available for allocation, > + * and (2) extended during allocation by block splits, which add the > + * resulting sub-blocks for subsequent finer-grained allocation. > + * @cursor: Pointer to current root index, advanced when iterating roots. > + * Pass in a value >= mm->n_roots to disable root iteration > entirely, > + * restricting block acquisition to @dfs only; this is used in the > + * trim scenario where only pre-split sub-blocks should be > considered. > + * > + * Return: Pointer to the acquired block on success, ERR_PTR(-ENOSPC) when no > + * more blocks are available. > + */ > +static struct gpu_buddy_block* > +__get_candidate_block(struct gpu_buddy *mm, struct list_head *dfs, > + uint32_t *cursor) > +{ > + struct gpu_buddy_block *block; > + > + block = list_first_entry_or_null(dfs, > + struct gpu_buddy_block, > + tmp_link); > + if (block) { > + list_del(&block->tmp_link); > + return block; > + } > + > + if (*cursor >= mm->n_roots) > + return ERR_PTR(-ENOSPC); > + > + return mm->roots[(*cursor)++]; > +} > + > static struct gpu_buddy_block * > __alloc_range_bias(struct gpu_buddy *mm, > u64 start, u64 end, > @@ -711,25 +746,18 @@ __alloc_range_bias(struct gpu_buddy *mm, > struct gpu_buddy_block *block; > LIST_HEAD(dfs); > int err; > - int i; > + uint32_t cursor = 0; > > end = end - 1; > > - for (i = 0; i < mm->n_roots; ++i) > - list_add_tail(&mm->roots[i]->tmp_link, &dfs); > - > do { > u64 block_start; > u64 block_end; > > - block = list_first_entry_or_null(&dfs, > - struct gpu_buddy_block, > - tmp_link); > - if (!block) > + block = __get_candidate_block(mm, &dfs, &cursor); > + if (IS_ERR(block)) > break; > > - list_del(&block->tmp_link); > - > if (gpu_buddy_block_order(block) < order) > continue; > > @@ -1023,6 +1051,7 @@ static int __alloc_range(struct gpu_buddy *mm, > LIST_HEAD(allocated); > u64 end; > int err; > + uint32_t cursor = list_empty(dfs) ? 0 : mm->n_roots; > > end = start + size - 1; > > @@ -1030,14 +1059,10 @@ static int __alloc_range(struct gpu_buddy *mm, > u64 block_start; > u64 block_end; > > - block = list_first_entry_or_null(dfs, > - struct gpu_buddy_block, > - tmp_link); > - if (!block) > + block = __get_candidate_block(mm, dfs, &cursor); > + if (IS_ERR(block)) > break; > > - list_del(&block->tmp_link); > - > block_start = gpu_buddy_block_offset(block); > block_end = block_start + gpu_buddy_block_size(mm, block) - > 1; > > @@ -1109,10 +1134,6 @@ static int __gpu_buddy_alloc_range(struct gpu_buddy > *mm, > struct list_head *blocks) > { > LIST_HEAD(dfs); > - int i; > - > - 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, total_allocated_on_err); > -- > 2.34.1 >
