From: Chengming Zhou <[email protected]>
The flush state machine use a double list to link all inflight
flush_data requests, to avoid issuing separate post-flushes for
these flush_data requests which shared PREFLUSH.
So we can't reuse rq->queuelist, this is why we need rq->flush.list
In preparation of the next patch that reuse rq->queuelist for flush
state machine, we change the double linked list to a u64 counter,
which count all inflight flush_data requests.
This is ok since we only need to know if there is any inflight
flush_data request, so a u64 counter is good. The only problem I can
think of is that u64 counter may overflow, which should be unlikely happen.
Signed-off-by: Chengming Zhou <[email protected]>
---
block/blk-flush.c | 9 +++++----
block/blk.h | 5 ++---
2 files changed, 7 insertions(+), 7 deletions(-)
diff --git a/block/blk-flush.c b/block/blk-flush.c
index dba392cf22be..bb7adfc2a5da 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -187,7 +187,8 @@ static void blk_flush_complete_seq(struct request *rq,
break;
case REQ_FSEQ_DATA:
- list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
+ list_del_init(&rq->flush.list);
+ fq->flush_data_in_flight++;
spin_lock(&q->requeue_lock);
list_add_tail(&rq->queuelist, &q->flush_list);
spin_unlock(&q->requeue_lock);
@@ -299,7 +300,7 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
return;
/* C2 and C3 */
- if (!list_empty(&fq->flush_data_in_flight) &&
+ if (fq->flush_data_in_flight &&
time_before(jiffies,
fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
return;
@@ -374,6 +375,7 @@ static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
* the comment in flush_end_io().
*/
spin_lock_irqsave(&fq->mq_flush_lock, flags);
+ fq->flush_data_in_flight--;
blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
@@ -445,7 +447,7 @@ bool blk_insert_flush(struct request *rq)
blk_rq_init_flush(rq);
rq->flush.seq |= REQ_FSEQ_POSTFLUSH;
spin_lock_irq(&fq->mq_flush_lock);
- list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
+ fq->flush_data_in_flight++;
spin_unlock_irq(&fq->mq_flush_lock);
return false;
default:
@@ -496,7 +498,6 @@ struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
INIT_LIST_HEAD(&fq->flush_queue[0]);
INIT_LIST_HEAD(&fq->flush_queue[1]);
- INIT_LIST_HEAD(&fq->flush_data_in_flight);
return fq;
diff --git a/block/blk.h b/block/blk.h
index 608c5dcc516b..686712e13835 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -15,15 +15,14 @@ struct elevator_type;
extern struct dentry *blk_debugfs_root;
struct blk_flush_queue {
+ spinlock_t mq_flush_lock;
unsigned int flush_pending_idx:1;
unsigned int flush_running_idx:1;
blk_status_t rq_status;
unsigned long flush_pending_since;
struct list_head flush_queue[2];
- struct list_head flush_data_in_flight;
+ unsigned long flush_data_in_flight;
struct request *flush_rq;
-
- spinlock_t mq_flush_lock;
};
bool is_flush_rq(struct request *req);
--
2.39.2
On Wed, Jun 28, 2023 at 12:55:49PM +0800, Chengming Zhou wrote:
> On 2023/6/28 12:13, Ming Lei wrote:
> > On Tue, Jun 27, 2023 at 08:08:52PM +0800, [email protected] wrote:
> >> From: Chengming Zhou <[email protected]>
> >>
> >> The flush state machine use a double list to link all inflight
> >> flush_data requests, to avoid issuing separate post-flushes for
> >> these flush_data requests which shared PREFLUSH.
> >>
> >> So we can't reuse rq->queuelist, this is why we need rq->flush.list
> >>
> >> In preparation of the next patch that reuse rq->queuelist for flush
> >> state machine, we change the double linked list to a u64 counter,
> >> which count all inflight flush_data requests.
> >>
> >> This is ok since we only need to know if there is any inflight
> >> flush_data request, so a u64 counter is good. The only problem I can
> >> think of is that u64 counter may overflow, which should be unlikely happen.
> >
> > It won't overflow, q->nr_requests is 'unsigned long', which should have
> > been limited to one more reasonable value, such as 2 * BLK_MQ_MAX_DEPTH, so
> > u16 should be big enough in theory.
>
> Ah, right. q->nr_requests is 'unsigned long' and q->queue_depth is 'unsigned int',
> so 'unsigned long' counter here won't overflow.
Not like q->nr_requests, q->queue_depth usually means the whole queue's depth,
which may cover all hw queue's depth. And it is only used by scsi, but it
should be held in "unsigned short" too.
>
> Should I change it to smaller 'unsigned short' or just leave it as 'unsigned long' ?
> (Now the size of struct blk_flush_queue is exactly 64 bytes)
You have to limit q->nr_requests first, which may need a bit more work for avoiding
compiling warning or sort of thing. And 64k is big enough for holding per-queue
scheduler request.
Once it is done, it is fine to define this counter as 'unsigned short'.
Thanks,
Ming
On Tue, Jun 27, 2023 at 08:08:52PM +0800, [email protected] wrote:
> From: Chengming Zhou <[email protected]>
>
> The flush state machine use a double list to link all inflight
> flush_data requests, to avoid issuing separate post-flushes for
> these flush_data requests which shared PREFLUSH.
>
> So we can't reuse rq->queuelist, this is why we need rq->flush.list
>
> In preparation of the next patch that reuse rq->queuelist for flush
> state machine, we change the double linked list to a u64 counter,
> which count all inflight flush_data requests.
>
> This is ok since we only need to know if there is any inflight
> flush_data request, so a u64 counter is good. The only problem I can
> think of is that u64 counter may overflow, which should be unlikely happen.
It won't overflow, q->nr_requests is 'unsigned long', which should have
been limited to one more reasonable value, such as 2 * BLK_MQ_MAX_DEPTH, so
u16 should be big enough in theory.
>
> Signed-off-by: Chengming Zhou <[email protected]>
> ---
> block/blk-flush.c | 9 +++++----
> block/blk.h | 5 ++---
> 2 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/block/blk-flush.c b/block/blk-flush.c
> index dba392cf22be..bb7adfc2a5da 100644
> --- a/block/blk-flush.c
> +++ b/block/blk-flush.c
> @@ -187,7 +187,8 @@ static void blk_flush_complete_seq(struct request *rq,
> break;
>
> case REQ_FSEQ_DATA:
> - list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
> + list_del_init(&rq->flush.list);
> + fq->flush_data_in_flight++;
> spin_lock(&q->requeue_lock);
> list_add_tail(&rq->queuelist, &q->flush_list);
> spin_unlock(&q->requeue_lock);
> @@ -299,7 +300,7 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
> return;
>
> /* C2 and C3 */
> - if (!list_empty(&fq->flush_data_in_flight) &&
> + if (fq->flush_data_in_flight &&
> time_before(jiffies,
> fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
> return;
> @@ -374,6 +375,7 @@ static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
> * the comment in flush_end_io().
> */
> spin_lock_irqsave(&fq->mq_flush_lock, flags);
> + fq->flush_data_in_flight--;
> blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
> spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
>
> @@ -445,7 +447,7 @@ bool blk_insert_flush(struct request *rq)
> blk_rq_init_flush(rq);
> rq->flush.seq |= REQ_FSEQ_POSTFLUSH;
> spin_lock_irq(&fq->mq_flush_lock);
> - list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
> + fq->flush_data_in_flight++;
> spin_unlock_irq(&fq->mq_flush_lock);
> return false;
> default:
> @@ -496,7 +498,6 @@ struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
>
> INIT_LIST_HEAD(&fq->flush_queue[0]);
> INIT_LIST_HEAD(&fq->flush_queue[1]);
> - INIT_LIST_HEAD(&fq->flush_data_in_flight);
>
> return fq;
>
> diff --git a/block/blk.h b/block/blk.h
> index 608c5dcc516b..686712e13835 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -15,15 +15,14 @@ struct elevator_type;
> extern struct dentry *blk_debugfs_root;
>
> struct blk_flush_queue {
> + spinlock_t mq_flush_lock;
> unsigned int flush_pending_idx:1;
> unsigned int flush_running_idx:1;
> blk_status_t rq_status;
> unsigned long flush_pending_since;
> struct list_head flush_queue[2];
> - struct list_head flush_data_in_flight;
> + unsigned long flush_data_in_flight;
> struct request *flush_rq;
> -
> - spinlock_t mq_flush_lock;
> };
The part of replacing inflight data rq list with counter looks fine.
Thanks,
Ming
On 2023/6/28 12:13, Ming Lei wrote:
> On Tue, Jun 27, 2023 at 08:08:52PM +0800, [email protected] wrote:
>> From: Chengming Zhou <[email protected]>
>>
>> The flush state machine use a double list to link all inflight
>> flush_data requests, to avoid issuing separate post-flushes for
>> these flush_data requests which shared PREFLUSH.
>>
>> So we can't reuse rq->queuelist, this is why we need rq->flush.list
>>
>> In preparation of the next patch that reuse rq->queuelist for flush
>> state machine, we change the double linked list to a u64 counter,
>> which count all inflight flush_data requests.
>>
>> This is ok since we only need to know if there is any inflight
>> flush_data request, so a u64 counter is good. The only problem I can
>> think of is that u64 counter may overflow, which should be unlikely happen.
>
> It won't overflow, q->nr_requests is 'unsigned long', which should have
> been limited to one more reasonable value, such as 2 * BLK_MQ_MAX_DEPTH, so
> u16 should be big enough in theory.
Ah, right. q->nr_requests is 'unsigned long' and q->queue_depth is 'unsigned int',
so 'unsigned long' counter here won't overflow.
Should I change it to smaller 'unsigned short' or just leave it as 'unsigned long' ?
(Now the size of struct blk_flush_queue is exactly 64 bytes)
Thanks.
>
>>
>> Signed-off-by: Chengming Zhou <[email protected]>
>> ---
>> block/blk-flush.c | 9 +++++----
>> block/blk.h | 5 ++---
>> 2 files changed, 7 insertions(+), 7 deletions(-)
>>
>> diff --git a/block/blk-flush.c b/block/blk-flush.c
>> index dba392cf22be..bb7adfc2a5da 100644
>> --- a/block/blk-flush.c
>> +++ b/block/blk-flush.c
>> @@ -187,7 +187,8 @@ static void blk_flush_complete_seq(struct request *rq,
>> break;
>>
>> case REQ_FSEQ_DATA:
>> - list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
>> + list_del_init(&rq->flush.list);
>> + fq->flush_data_in_flight++;
>> spin_lock(&q->requeue_lock);
>> list_add_tail(&rq->queuelist, &q->flush_list);
>> spin_unlock(&q->requeue_lock);
>> @@ -299,7 +300,7 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
>> return;
>>
>> /* C2 and C3 */
>> - if (!list_empty(&fq->flush_data_in_flight) &&
>> + if (fq->flush_data_in_flight &&
>> time_before(jiffies,
>> fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
>> return;
>> @@ -374,6 +375,7 @@ static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
>> * the comment in flush_end_io().
>> */
>> spin_lock_irqsave(&fq->mq_flush_lock, flags);
>> + fq->flush_data_in_flight--;
>> blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
>> spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
>>
>> @@ -445,7 +447,7 @@ bool blk_insert_flush(struct request *rq)
>> blk_rq_init_flush(rq);
>> rq->flush.seq |= REQ_FSEQ_POSTFLUSH;
>> spin_lock_irq(&fq->mq_flush_lock);
>> - list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
>> + fq->flush_data_in_flight++;
>> spin_unlock_irq(&fq->mq_flush_lock);
>> return false;
>> default:
>> @@ -496,7 +498,6 @@ struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
>>
>> INIT_LIST_HEAD(&fq->flush_queue[0]);
>> INIT_LIST_HEAD(&fq->flush_queue[1]);
>> - INIT_LIST_HEAD(&fq->flush_data_in_flight);
>>
>> return fq;
>>
>> diff --git a/block/blk.h b/block/blk.h
>> index 608c5dcc516b..686712e13835 100644
>> --- a/block/blk.h
>> +++ b/block/blk.h
>> @@ -15,15 +15,14 @@ struct elevator_type;
>> extern struct dentry *blk_debugfs_root;
>>
>> struct blk_flush_queue {
>> + spinlock_t mq_flush_lock;
>> unsigned int flush_pending_idx:1;
>> unsigned int flush_running_idx:1;
>> blk_status_t rq_status;
>> unsigned long flush_pending_since;
>> struct list_head flush_queue[2];
>> - struct list_head flush_data_in_flight;
>> + unsigned long flush_data_in_flight;
>> struct request *flush_rq;
>> -
>> - spinlock_t mq_flush_lock;
>> };
>
> The part of replacing inflight data rq list with counter looks fine.
>
> Thanks,
> Ming
>
On 2023/6/28 15:22, Ming Lei wrote:
> On Wed, Jun 28, 2023 at 12:55:49PM +0800, Chengming Zhou wrote:
>> On 2023/6/28 12:13, Ming Lei wrote:
>>> On Tue, Jun 27, 2023 at 08:08:52PM +0800, [email protected] wrote:
>>>> From: Chengming Zhou <[email protected]>
>>>>
>>>> The flush state machine use a double list to link all inflight
>>>> flush_data requests, to avoid issuing separate post-flushes for
>>>> these flush_data requests which shared PREFLUSH.
>>>>
>>>> So we can't reuse rq->queuelist, this is why we need rq->flush.list
>>>>
>>>> In preparation of the next patch that reuse rq->queuelist for flush
>>>> state machine, we change the double linked list to a u64 counter,
>>>> which count all inflight flush_data requests.
>>>>
>>>> This is ok since we only need to know if there is any inflight
>>>> flush_data request, so a u64 counter is good. The only problem I can
>>>> think of is that u64 counter may overflow, which should be unlikely happen.
>>>
>>> It won't overflow, q->nr_requests is 'unsigned long', which should have
>>> been limited to one more reasonable value, such as 2 * BLK_MQ_MAX_DEPTH, so
>>> u16 should be big enough in theory.
>>
>> Ah, right. q->nr_requests is 'unsigned long' and q->queue_depth is 'unsigned int',
>> so 'unsigned long' counter here won't overflow.
>
> Not like q->nr_requests, q->queue_depth usually means the whole queue's depth,
> which may cover all hw queue's depth. And it is only used by scsi, but it
> should be held in "unsigned short" too.
>
>>
>> Should I change it to smaller 'unsigned short' or just leave it as 'unsigned long' ?
>> (Now the size of struct blk_flush_queue is exactly 64 bytes)
>
> You have to limit q->nr_requests first, which may need a bit more work for avoiding
> compiling warning or sort of thing. And 64k is big enough for holding per-queue
> scheduler request.
>
> Once it is done, it is fine to define this counter as 'unsigned short'.
>
Ok, I looked around these related code, found it maybe subtle to me for now.
So I'd better just leave it 'unsigned long' here. :)
Thanks.