[PATCH 14/17] blk-mq: move the srcu_struct used for quiescing to the tagset

[Sagi Grimberg]

On 10/26/22 11:48, Chao Leng wrote:
> 
> 
> On 2022/10/25 22:40, Christoph Hellwig wrote:
>> All I/O submissions have fairly similar latencies, and a tagset-wide
>> quiesce is a fairly common operation.
>>
>> Signed-off-by: Christoph Hellwig <hch at lst.de>
>> Reviewed-by: Keith Busch <kbusch at kernel.org>
>> Reviewed-by: Ming Lei <ming.lei at redhat.com>
>> Reviewed-by: Chao Leng <lengchao at huawei.com>
>> Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
>> Reviewed-by: Hannes Reinecke <hare at suse.de>
>> ---
>>   block/blk-core.c       | 27 +++++----------------------
>>   block/blk-mq.c         | 33 +++++++++++++++++++++++++--------
>>   block/blk-mq.h         | 14 +++++++-------
>>   block/blk-sysfs.c      |  9 ++-------
>>   block/blk.h            |  9 +--------
>>   block/genhd.c          |  2 +-
>>   include/linux/blk-mq.h |  4 ++++
>>   include/linux/blkdev.h |  9 ---------
>>   8 files changed, 45 insertions(+), 62 deletions(-)
>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 17667159482e0..3a2ed8dadf738 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -65,7 +65,6 @@ DEFINE_IDA(blk_queue_ida);
>>    * For queue allocation
>>    */
>>   struct kmem_cache *blk_requestq_cachep;
>> -struct kmem_cache *blk_requestq_srcu_cachep;
>>   /*
>>    * Controlling structure to kblockd
>> @@ -373,26 +372,20 @@ static void blk_timeout_work(struct work_struct 
>> *work)
>>   {
>>   }
>> -struct request_queue *blk_alloc_queue(int node_id, bool alloc_srcu)
>> +struct request_queue *blk_alloc_queue(int node_id)
>>   {
>>       struct request_queue *q;
>> -    q = kmem_cache_alloc_node(blk_get_queue_kmem_cache(alloc_srcu),
>> -            GFP_KERNEL | __GFP_ZERO, node_id);
>> +    q = kmem_cache_alloc_node(blk_requestq_cachep, GFP_KERNEL | 
>> __GFP_ZERO,
>> +                  node_id);
>>       if (!q)
>>           return NULL;
>> -    if (alloc_srcu) {
>> -        blk_queue_flag_set(QUEUE_FLAG_HAS_SRCU, q);
>> -        if (init_srcu_struct(q->srcu) != 0)
>> -            goto fail_q;
>> -    }
>> -
>>       q->last_merge = NULL;
>>       q->id = ida_alloc(&blk_queue_ida, GFP_KERNEL);
>>       if (q->id < 0)
>> -        goto fail_srcu;
>> +        goto fail_q;
>>       q->stats = blk_alloc_queue_stats();
>>       if (!q->stats)
>> @@ -435,11 +428,8 @@ struct request_queue *blk_alloc_queue(int 
>> node_id, bool alloc_srcu)
>>       blk_free_queue_stats(q->stats);
>>   fail_id:
>>       ida_free(&blk_queue_ida, q->id);
>> -fail_srcu:
>> -    if (alloc_srcu)
>> -        cleanup_srcu_struct(q->srcu);
>>   fail_q:
>> -    kmem_cache_free(blk_get_queue_kmem_cache(alloc_srcu), q);
>> +    kmem_cache_free(blk_requestq_cachep, q);
>>       return NULL;
>>   }
>> @@ -1184,9 +1174,6 @@ int __init blk_dev_init(void)
>>               sizeof_field(struct request, cmd_flags));
>>       BUILD_BUG_ON(REQ_OP_BITS + REQ_FLAG_BITS > 8 *
>>               sizeof_field(struct bio, bi_opf));
>> -    BUILD_BUG_ON(ALIGN(offsetof(struct request_queue, srcu),
>> -               __alignof__(struct request_queue)) !=
>> -             sizeof(struct request_queue));
>>       /* used for unplugging and affects IO latency/throughput - 
>> HIGHPRI */
>>       kblockd_workqueue = alloc_workqueue("kblockd",
>> @@ -1197,10 +1184,6 @@ int __init blk_dev_init(void)
>>       blk_requestq_cachep = kmem_cache_create("request_queue",
>>               sizeof(struct request_queue), 0, SLAB_PANIC, NULL);
>> -    blk_requestq_srcu_cachep = kmem_cache_create("request_queue_srcu",
>> -            sizeof(struct request_queue) +
>> -            sizeof(struct srcu_struct), 0, SLAB_PANIC, NULL);
>> -
>>       blk_debugfs_root = debugfs_create_dir("block", NULL);
>>       return 0;
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 802fdd3d737e3..6cbf34921e33f 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -261,8 +261,8 @@ EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait);
>>    */
>>   void blk_mq_wait_quiesce_done(struct request_queue *q)
>>   {
>> -    if (blk_queue_has_srcu(q))
>> -        synchronize_srcu(q->srcu);
>> +    if (q->tag_set->flags & BLK_MQ_F_BLOCKING)
>> +        synchronize_srcu(q->tag_set->srcu);
>>       else
>>           synchronize_rcu();
>>   }
>> @@ -3971,7 +3971,7 @@ static struct request_queue 
>> *blk_mq_init_queue_data(struct blk_mq_tag_set *set,
>>       struct request_queue *q;
>>       int ret;
>> -    q = blk_alloc_queue(set->numa_node, set->flags & BLK_MQ_F_BLOCKING);
>> +    q = blk_alloc_queue(set->numa_node);
>>       if (!q)
>>           return ERR_PTR(-ENOMEM);
>>       q->queuedata = queuedata;
>> @@ -4138,9 +4138,6 @@ static void blk_mq_update_poll_flag(struct 
>> request_queue *q)
>>   int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
>>           struct request_queue *q)
>>   {
>> -    WARN_ON_ONCE(blk_queue_has_srcu(q) !=
>> -            !!(set->flags & BLK_MQ_F_BLOCKING));
>> -
>>       /* mark the queue as mq asap */
>>       q->mq_ops = set->ops;
>> @@ -4398,9 +4395,19 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set 
>> *set)
>>        */
>>       if (set->nr_maps == 1 && set->nr_hw_queues > nr_cpu_ids)
>>           set->nr_hw_queues = nr_cpu_ids;
>> +
>> +    if (set->flags & BLK_MQ_F_BLOCKING) {
>> +        set->srcu = kmalloc(sizeof(*set->srcu), GFP_KERNEL);
> Memory with contiguous physical addresses is not necessary, maybe it is 
> a better choice to use kvmalloc,
> because sizeof(*set->srcu) is a little large.
> kvmalloc() is more friendly to scenarios where memory is insufficient 
> and running for a long time.

Huh?

(gdb) p sizeof(struct srcu_struct)
$1 = 392