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SubjectRe: [PATCH v6 6/6] locking/lockdep: Reuse freed chain_hlocks entries
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On 2/6/20 11:16 AM, Peter Zijlstra wrote:
> 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.

Yes, that is simpler. I can send out an updated patch if you want, or
you can apply the change when you pull the patch.

Thanks,
Longman

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