Messages in this thread | | | Date | Thu, 6 Feb 2020 17:16:40 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v6 6/6] locking/lockdep: Reuse freed chain_hlocks entries |
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On Thu, Feb 06, 2020 at 10:24:08AM -0500, Waiman Long wrote: > +static int alloc_chain_hlocks(int req) > +{ > + int bucket, curr, size; > + > + /* > + * We rely on the MSB to act as an escape bit to denote freelist > + * pointers. Make sure this bit isn't set in 'normal' class_idx usage. > + */ > + BUILD_BUG_ON((MAX_LOCKDEP_KEYS-1) & CHAIN_BLK_FLAG); > + > + init_data_structures_once(); > + > + if (nr_free_chain_hlocks < req) > + return -1; > + > + /* > + * We require a minimum of 2 (u16) entries to encode a freelist > + * 'pointer'. > + */ > + req = max(req, 2); > + bucket = size_to_bucket(req); > + curr = chain_block_buckets[bucket]; > + > + if (bucket && (curr >= 0)) { > + del_chain_block(bucket, req, chain_block_next(curr)); > + return curr; > + } else if (bucket) { > + /* Try bucket 0 */ > + curr = chain_block_buckets[0]; > + }
if (bucket) { if (curr >= 0) { del_chain_block(bucket, req, chain_block_next(curr)); return curr; } /* Try bucket 0 */ curr = chain_block_bucket[0]; }
reads much easier IMO.
> + /* > + * The variable sized freelist is sorted by size; the first entry is > + * the largest. Use it if it fits. > + */ > + if (curr >= 0) { > + size = chain_block_size(curr); > + if (likely(size >= req)) { > + del_chain_block(0, size, chain_block_next(curr)); > + add_chain_block(curr + req, size - req); > + return curr; > + } > + } > + > + /* > + * Last resort, split a block in a larger sized bucket. > + */ > + for (size = MAX_CHAIN_BUCKETS; size > req; size--) { > + bucket = size_to_bucket(size); > + curr = chain_block_buckets[bucket]; > + if (curr < 0) > + continue; > + > + del_chain_block(bucket, size, chain_block_next(curr)); > + add_chain_block(curr + req, size - req); > + return curr; > + } > + > + return -1; > +}
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