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[PATCH 0/4] block: some misc changes

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  [PATCH 0/4] block: some misc changes Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
    [PATCH 1/4] block: setup bi_phys_segments after splitting Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
      Re: [PATCH 1/4] block: setup bi_phys_segments after splitting Jeff Moyer <jmoyer@redhat.com> - 2015-10-15 17:20 +0200
    [PATCH 3/4] blk-mq: check bio_mergeable() early before merging Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
      Re: [PATCH 3/4] blk-mq: check bio_mergeable() early before merging Jeff Moyer <jmoyer@redhat.com> - 2015-10-15 17:30 +0200
        Re: [PATCH 3/4] blk-mq: check bio_mergeable() early before merging Ming Lei <ming.lei@canonical.com> - 2015-10-16 02:30 +0200
    [PATCH 4/4] blk-mq: mark ctx as pending at batch in flush plug path Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
      Re: [PATCH 4/4] blk-mq: mark ctx as pending at batch in flush plug path Jeff Moyer <jmoyer@redhat.com> - 2015-10-15 17:30 +0200
        Re: [PATCH 4/4] blk-mq: mark ctx as pending at batch in flush plug path Ming Lei <ming.lei@canonical.com> - 2015-10-16 02:30 +0200
    [PATCH 2/4] block: avoid to merge splitted bio Ming Lei <ming.lei@canonical.com> - 2015-10-14 05:40 +0200
      Re: [PATCH 2/4] block: avoid to merge splitted bio Jeff Moyer <jmoyer@redhat.com> - 2015-10-15 17:20 +0200

#1246283 — [PATCH 0/4] block: some misc changes

Hi,

The 1st three patches are optimizations related with bio splitting.

The 4th patch is to mark ctx as pending at batch in flush plug path.

Thanks,

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#1246284 — [PATCH 1/4] block: setup bi_phys_segments after splitting

The number of bio->bi_phys_segments is always obtained
during bio splitting, so it is natural to setup it
just after bio splitting, then we can avoid to compute
nr_segment again during merge.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 block/blk-merge.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index c4e9c37..22293fd 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -11,13 +11,16 @@
 
 static struct bio *blk_bio_discard_split(struct request_queue *q,
 					 struct bio *bio,
-					 struct bio_set *bs)
+					 struct bio_set *bs,
+					 unsigned *nsegs)
 {
 	unsigned int max_discard_sectors, granularity;
 	int alignment;
 	sector_t tmp;
 	unsigned split_sectors;
 
+	*nsegs = 1;
+
 	/* Zero-sector (unknown) and one-sector granularities are the same.  */
 	granularity = max(q->limits.discard_granularity >> 9, 1U);
 
@@ -51,8 +54,11 @@ static struct bio *blk_bio_discard_split(struct request_queue *q,
 
 static struct bio *blk_bio_write_same_split(struct request_queue *q,
 					    struct bio *bio,
-					    struct bio_set *bs)
+					    struct bio_set *bs,
+					    unsigned *nsegs)
 {
+	*nsegs = 1;
+
 	if (!q->limits.max_write_same_sectors)
 		return NULL;
 
@@ -64,7 +70,8 @@ static struct bio *blk_bio_write_same_split(struct request_queue *q,
 
 static struct bio *blk_bio_segment_split(struct request_queue *q,
 					 struct bio *bio,
-					 struct bio_set *bs)
+					 struct bio_set *bs,
+					 unsigned *segs)
 {
 	struct bio_vec bv, bvprv, *bvprvp = NULL;
 	struct bvec_iter iter;
@@ -106,22 +113,30 @@ new_segment:
 		sectors += bv.bv_len >> 9;
 	}
 
+	*segs = nsegs;
 	return NULL;
 split:
+	*segs = nsegs;
 	return bio_split(bio, sectors, GFP_NOIO, bs);
 }
 
 void blk_queue_split(struct request_queue *q, struct bio **bio,
 		     struct bio_set *bs)
 {
-	struct bio *split;
+	struct bio *split, *res;
+	unsigned nsegs;
 
 	if ((*bio)->bi_rw & REQ_DISCARD)
-		split = blk_bio_discard_split(q, *bio, bs);
+		split = blk_bio_discard_split(q, *bio, bs, &nsegs);
 	else if ((*bio)->bi_rw & REQ_WRITE_SAME)
-		split = blk_bio_write_same_split(q, *bio, bs);
+		split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
 	else
-		split = blk_bio_segment_split(q, *bio, q->bio_split);
+		split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
+
+	/* physical segments can be figured out during splitting */
+	res = split ? split : *bio;
+	res->bi_phys_segments = nsegs;
+	bio_set_flag(res, BIO_SEG_VALID);
 
 	if (split) {
 		bio_chain(split, *bio);
-- 
1.9.1

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#1247882 — Re: [PATCH 1/4] block: setup bi_phys_segments after splitting

Ming Lei <ming.lei@canonical.com> writes:

> The number of bio->bi_phys_segments is always obtained
> during bio splitting, so it is natural to setup it
> just after bio splitting, then we can avoid to compute
> nr_segment again during merge.
>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

> ---
>  block/blk-merge.c | 29 ++++++++++++++++++++++-------
>  1 file changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index c4e9c37..22293fd 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -11,13 +11,16 @@
>  
>  static struct bio *blk_bio_discard_split(struct request_queue *q,
>  					 struct bio *bio,
> -					 struct bio_set *bs)
> +					 struct bio_set *bs,
> +					 unsigned *nsegs)
>  {
>  	unsigned int max_discard_sectors, granularity;
>  	int alignment;
>  	sector_t tmp;
>  	unsigned split_sectors;
>  
> +	*nsegs = 1;
> +
>  	/* Zero-sector (unknown) and one-sector granularities are the same.  */
>  	granularity = max(q->limits.discard_granularity >> 9, 1U);
>  
> @@ -51,8 +54,11 @@ static struct bio *blk_bio_discard_split(struct request_queue *q,
>  
>  static struct bio *blk_bio_write_same_split(struct request_queue *q,
>  					    struct bio *bio,
> -					    struct bio_set *bs)
> +					    struct bio_set *bs,
> +					    unsigned *nsegs)
>  {
> +	*nsegs = 1;
> +
>  	if (!q->limits.max_write_same_sectors)
>  		return NULL;
>  
> @@ -64,7 +70,8 @@ static struct bio *blk_bio_write_same_split(struct request_queue *q,
>  
>  static struct bio *blk_bio_segment_split(struct request_queue *q,
>  					 struct bio *bio,
> -					 struct bio_set *bs)
> +					 struct bio_set *bs,
> +					 unsigned *segs)
>  {
>  	struct bio_vec bv, bvprv, *bvprvp = NULL;
>  	struct bvec_iter iter;
> @@ -106,22 +113,30 @@ new_segment:
>  		sectors += bv.bv_len >> 9;
>  	}
>  
> +	*segs = nsegs;
>  	return NULL;
>  split:
> +	*segs = nsegs;
>  	return bio_split(bio, sectors, GFP_NOIO, bs);
>  }
>  
>  void blk_queue_split(struct request_queue *q, struct bio **bio,
>  		     struct bio_set *bs)
>  {
> -	struct bio *split;
> +	struct bio *split, *res;
> +	unsigned nsegs;
>  
>  	if ((*bio)->bi_rw & REQ_DISCARD)
> -		split = blk_bio_discard_split(q, *bio, bs);
> +		split = blk_bio_discard_split(q, *bio, bs, &nsegs);
>  	else if ((*bio)->bi_rw & REQ_WRITE_SAME)
> -		split = blk_bio_write_same_split(q, *bio, bs);
> +		split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
>  	else
> -		split = blk_bio_segment_split(q, *bio, q->bio_split);
> +		split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
> +
> +	/* physical segments can be figured out during splitting */
> +	res = split ? split : *bio;
> +	res->bi_phys_segments = nsegs;
> +	bio_set_flag(res, BIO_SEG_VALID);
>  
>  	if (split) {
>  		bio_chain(split, *bio);
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#1246285 — [PATCH 3/4] blk-mq: check bio_mergeable() early before merging

It isn't necessary to try to merge the bio which is marked
as NOMERGE.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 block/blk-mq.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 546b3b8..deb5f4c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -671,6 +671,9 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
 	struct request *rq;
 	int checked = 8;
 
+	if (!bio_mergeable(bio))
+		return false;
+
 	list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
 		int el_ret;
 
@@ -1140,7 +1143,7 @@ static inline bool blk_mq_merge_queue_io(struct blk_mq_hw_ctx *hctx,
 					 struct blk_mq_ctx *ctx,
 					 struct request *rq, struct bio *bio)
 {
-	if (!hctx_allow_merges(hctx)) {
+	if (!hctx_allow_merges(hctx) || !bio_mergeable(bio)) {
 		blk_mq_bio_to_request(rq, bio);
 		spin_lock(&ctx->lock);
 insert_rq:
-- 
1.9.1

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#1247898 — Re: [PATCH 3/4] blk-mq: check bio_mergeable() early before merging

Ming Lei <ming.lei@canonical.com> writes:

> It isn't necessary to try to merge the bio which is marked
> as NOMERGE.
>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>
> ---
>  block/blk-mq.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 546b3b8..deb5f4c 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -671,6 +671,9 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
>  	struct request *rq;
>  	int checked = 8;
>  
> +	if (!bio_mergeable(bio))
> +		return false;
> +
>  	list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
>  		int el_ret;
>  
> @@ -1140,7 +1143,7 @@ static inline bool blk_mq_merge_queue_io(struct blk_mq_hw_ctx *hctx,
>  					 struct blk_mq_ctx *ctx,
>  					 struct request *rq, struct bio *bio)
>  {
> -	if (!hctx_allow_merges(hctx)) {
> +	if (!hctx_allow_merges(hctx) || !bio_mergeable(bio)) {
>  		blk_mq_bio_to_request(rq, bio);
>  		spin_lock(&ctx->lock);
>  insert_rq:

blk_mq_attempt_merge is only called from blk_mq_merge_queue_io.  So, by
adding the conditional in blk_mq_merge_queue_io, you don't need any
change in blk_mq_attempt_merge.

Also, why haven't you updated the non-multiqueue code paths similarly?

Cheers,
Jeff
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#1248270 — Re: [PATCH 3/4] blk-mq: check bio_mergeable() early before merging

On Thu, Oct 15, 2015 at 11:21 PM, Jeff Moyer <jmoyer@redhat.com> wrote:
> Ming Lei <ming.lei@canonical.com> writes:
>
>> It isn't necessary to try to merge the bio which is marked
>> as NOMERGE.
>>
>> Signed-off-by: Ming Lei <ming.lei@canonical.com>
>> ---
>>  block/blk-mq.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 546b3b8..deb5f4c 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -671,6 +671,9 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
>>       struct request *rq;
>>       int checked = 8;
>>
>> +     if (!bio_mergeable(bio))
>> +             return false;
>> +
>>       list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
>>               int el_ret;
>>
>> @@ -1140,7 +1143,7 @@ static inline bool blk_mq_merge_queue_io(struct blk_mq_hw_ctx *hctx,
>>                                        struct blk_mq_ctx *ctx,
>>                                        struct request *rq, struct bio *bio)
>>  {
>> -     if (!hctx_allow_merges(hctx)) {
>> +     if (!hctx_allow_merges(hctx) || !bio_mergeable(bio)) {
>>               blk_mq_bio_to_request(rq, bio);
>>               spin_lock(&ctx->lock);
>>  insert_rq:
>
> blk_mq_attempt_merge is only called from blk_mq_merge_queue_io.  So, by
> adding the conditional in blk_mq_merge_queue_io, you don't need any
> change in blk_mq_attempt_merge.

OK.

>
> Also, why haven't you updated the non-multiqueue code paths similarly?

Will do it in v1.

>
> Cheers,
> Jeff
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#1246286 — [PATCH 4/4] blk-mq: mark ctx as pending at batch in flush plug path

Most of times, flush plug should be the hottest I/O path,
so mark ctx as pending after all requests in the list are
inserted.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 block/blk-mq.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index deb5f4c..1c943b9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -993,18 +993,25 @@ void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
 }
 EXPORT_SYMBOL(blk_mq_delay_queue);
 
-static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
-				    struct request *rq, bool at_head)
+static inline void __blk_mq_insert_req_list(struct blk_mq_hw_ctx *hctx,
+					    struct blk_mq_ctx *ctx,
+					    struct request *rq,
+					    bool at_head)
 {
-	struct blk_mq_ctx *ctx = rq->mq_ctx;
-
 	trace_block_rq_insert(hctx->queue, rq);
 
 	if (at_head)
 		list_add(&rq->queuelist, &ctx->rq_list);
 	else
 		list_add_tail(&rq->queuelist, &ctx->rq_list);
+}
+
+static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
+				    struct request *rq, bool at_head)
+{
+	struct blk_mq_ctx *ctx = rq->mq_ctx;
 
+	__blk_mq_insert_req_list(hctx, ctx, rq, at_head);
 	blk_mq_hctx_mark_pending(hctx, ctx);
 }
 
@@ -1060,8 +1067,9 @@ static void blk_mq_insert_requests(struct request_queue *q,
 		rq = list_first_entry(list, struct request, queuelist);
 		list_del_init(&rq->queuelist);
 		rq->mq_ctx = ctx;
-		__blk_mq_insert_request(hctx, rq, false);
+		__blk_mq_insert_req_list(hctx, ctx, rq, false);
 	}
+	blk_mq_hctx_mark_pending(hctx, ctx);
 	spin_unlock(&ctx->lock);
 
 	blk_mq_run_hw_queue(hctx, from_schedule);
-- 
1.9.1

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#1247896 — Re: [PATCH 4/4] blk-mq: mark ctx as pending at batch in flush plug path

Ming Lei <ming.lei@canonical.com> writes:

> Most of times, flush plug should be the hottest I/O path,
> so mark ctx as pending after all requests in the list are
> inserted.

Hi, Ming,

Did you see some performance gain from this?

-Jeff

>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>
> ---
>  block/blk-mq.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index deb5f4c..1c943b9 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -993,18 +993,25 @@ void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
>  }
>  EXPORT_SYMBOL(blk_mq_delay_queue);
>  
> -static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
> -				    struct request *rq, bool at_head)
> +static inline void __blk_mq_insert_req_list(struct blk_mq_hw_ctx *hctx,
> +					    struct blk_mq_ctx *ctx,
> +					    struct request *rq,
> +					    bool at_head)
>  {
> -	struct blk_mq_ctx *ctx = rq->mq_ctx;
> -
>  	trace_block_rq_insert(hctx->queue, rq);
>  
>  	if (at_head)
>  		list_add(&rq->queuelist, &ctx->rq_list);
>  	else
>  		list_add_tail(&rq->queuelist, &ctx->rq_list);
> +}
> +
> +static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
> +				    struct request *rq, bool at_head)
> +{
> +	struct blk_mq_ctx *ctx = rq->mq_ctx;
>  
> +	__blk_mq_insert_req_list(hctx, ctx, rq, at_head);
>  	blk_mq_hctx_mark_pending(hctx, ctx);
>  }
>  
> @@ -1060,8 +1067,9 @@ static void blk_mq_insert_requests(struct request_queue *q,
>  		rq = list_first_entry(list, struct request, queuelist);
>  		list_del_init(&rq->queuelist);
>  		rq->mq_ctx = ctx;
> -		__blk_mq_insert_request(hctx, rq, false);
> +		__blk_mq_insert_req_list(hctx, ctx, rq, false);
>  	}
> +	blk_mq_hctx_mark_pending(hctx, ctx);
>  	spin_unlock(&ctx->lock);
>  
>  	blk_mq_run_hw_queue(hctx, from_schedule);
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#1248272 — Re: [PATCH 4/4] blk-mq: mark ctx as pending at batch in flush plug path

Hi Jeff,

On Thu, Oct 15, 2015 at 11:26 PM, Jeff Moyer <jmoyer@redhat.com> wrote:
> Ming Lei <ming.lei@canonical.com> writes:
>
>> Most of times, flush plug should be the hottest I/O path,
>> so mark ctx as pending after all requests in the list are
>> inserted.
>
> Hi, Ming,
>
> Did you see some performance gain from this?

Not done the test yet, but I think it is the correct thing to do because
the flag can be cleared quite frequently from other CPUs, and the numberof
marking pending can be decreased to ~1/16 of previous one.

>
> -Jeff
>
>>
>> Signed-off-by: Ming Lei <ming.lei@canonical.com>
>> ---
>>  block/blk-mq.c | 18 +++++++++++++-----
>>  1 file changed, 13 insertions(+), 5 deletions(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index deb5f4c..1c943b9 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -993,18 +993,25 @@ void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
>>  }
>>  EXPORT_SYMBOL(blk_mq_delay_queue);
>>
>> -static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
>> -                                 struct request *rq, bool at_head)
>> +static inline void __blk_mq_insert_req_list(struct blk_mq_hw_ctx *hctx,
>> +                                         struct blk_mq_ctx *ctx,
>> +                                         struct request *rq,
>> +                                         bool at_head)
>>  {
>> -     struct blk_mq_ctx *ctx = rq->mq_ctx;
>> -
>>       trace_block_rq_insert(hctx->queue, rq);
>>
>>       if (at_head)
>>               list_add(&rq->queuelist, &ctx->rq_list);
>>       else
>>               list_add_tail(&rq->queuelist, &ctx->rq_list);
>> +}
>> +
>> +static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
>> +                                 struct request *rq, bool at_head)
>> +{
>> +     struct blk_mq_ctx *ctx = rq->mq_ctx;
>>
>> +     __blk_mq_insert_req_list(hctx, ctx, rq, at_head);
>>       blk_mq_hctx_mark_pending(hctx, ctx);
>>  }
>>
>> @@ -1060,8 +1067,9 @@ static void blk_mq_insert_requests(struct request_queue *q,
>>               rq = list_first_entry(list, struct request, queuelist);
>>               list_del_init(&rq->queuelist);
>>               rq->mq_ctx = ctx;
>> -             __blk_mq_insert_request(hctx, rq, false);
>> +             __blk_mq_insert_req_list(hctx, ctx, rq, false);
>>       }
>> +     blk_mq_hctx_mark_pending(hctx, ctx);
>>       spin_unlock(&ctx->lock);
>>
>>       blk_mq_run_hw_queue(hctx, from_schedule);
> --
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#1246287 — [PATCH 2/4] block: avoid to merge splitted bio

The splitted bio has been already too fat to merge, so mark it
as NOMERGE.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 block/blk-merge.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 22293fd..de5716d8 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -139,6 +139,9 @@ void blk_queue_split(struct request_queue *q, struct bio **bio,
 	bio_set_flag(res, BIO_SEG_VALID);
 
 	if (split) {
+		/* there isn't chance to merge the splitted bio */
+		split->bi_rw |= REQ_NOMERGE;
+
 		bio_chain(split, *bio);
 		generic_make_request(*bio);
 		*bio = split;
-- 
1.9.1

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#1247879 — Re: [PATCH 2/4] block: avoid to merge splitted bio

Ming Lei <ming.lei@canonical.com> writes:

> The splitted bio has been already too fat to merge, so mark it
> as NOMERGE.
>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

> ---
>  block/blk-merge.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 22293fd..de5716d8 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -139,6 +139,9 @@ void blk_queue_split(struct request_queue *q, struct bio **bio,
>  	bio_set_flag(res, BIO_SEG_VALID);
>  
>  	if (split) {
> +		/* there isn't chance to merge the splitted bio */
> +		split->bi_rw |= REQ_NOMERGE;
> +
>  		bio_chain(split, *bio);
>  		generic_make_request(*bio);
>  		*bio = split;
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