[PATCH] f2fs: fix long latency due to discard during umount

[PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

F2FS already has a default timeout of 5 secs for discards that
can be issued during umount, but it can take more than the 5 sec
timeout if the underlying UFS device queue is already full and there
are no more available free tags to be used. In that case, submit_bio()
will wait for the already queued discard requests to complete to get
a free tag, which can potentially take way more than 5 sec.

Fix this by submitting the discard requests with REQ_NOWAIT
flags during umount. This will return -EAGAIN for UFS queue/tag full
scenario without waiting in the context of submit_bio(). The FS can
then handle these requests by retrying again within the stipulated
discard timeout period to avoid long latencies.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
---
 fs/f2fs/segment.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index fb3e531..a06bbac 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
 	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
 	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
 					&(dcc->fstrim_list) : &(dcc->wait_list);
-	int flag = dpolicy->sync ? REQ_SYNC : 0;
+	int flag;
 	block_t lstart, start, len, total_len;
 	int err = 0;
 
+	flag = dpolicy->sync ? REQ_SYNC : 0;
+	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
+
 	if (dc->state != D_PREP)
 		return 0;
 
@@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
 		bio->bi_end_io = f2fs_submit_discard_endio;
 		bio->bi_opf |= flag;
 		submit_bio(bio);
+		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
+			dc->state = D_PREP;
+			err = dc->error;
+			break;
+		}
 
 		atomic_inc(&dcc->issued_discard);
 
@@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 			}
 
 			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
+			if (dc->error == -EAGAIN) {
+				congestion_wait(BLK_RW_ASYNC, HZ/50);
+				__relocate_discard_cmd(dcc, dc);
+			}
 
 			if (issued >= dpolicy->max_requests)
 				break;
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Jaegeuk Kim]

On 03/12, Sahitya Tummala wrote:
> F2FS already has a default timeout of 5 secs for discards that
> can be issued during umount, but it can take more than the 5 sec
> timeout if the underlying UFS device queue is already full and there
> are no more available free tags to be used. In that case, submit_bio()
> will wait for the already queued discard requests to complete to get
> a free tag, which can potentially take way more than 5 sec.
> 
> Fix this by submitting the discard requests with REQ_NOWAIT
> flags during umount. This will return -EAGAIN for UFS queue/tag full
> scenario without waiting in the context of submit_bio(). The FS can
> then handle these requests by retrying again within the stipulated
> discard timeout period to avoid long latencies.
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> ---
>  fs/f2fs/segment.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index fb3e531..a06bbac 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> +	int flag;
>  	block_t lstart, start, len, total_len;
>  	int err = 0;
>  
> +	flag = dpolicy->sync ? REQ_SYNC : 0;
> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> +
>  	if (dc->state != D_PREP)
>  		return 0;
>  
> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  		bio->bi_end_io = f2fs_submit_discard_endio;
>  		bio->bi_opf |= flag;
>  		submit_bio(bio);
> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> +			dc->state = D_PREP;
> +			err = dc->error;
> +			break;
> +		}
>  
>  		atomic_inc(&dcc->issued_discard);
>  
> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  			}
>  
>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> +			if (dc->error == -EAGAIN) {
> +				congestion_wait(BLK_RW_ASYNC, HZ/50);

						--> need to be DEFAULT_IO_TIMEOUT

> +				__relocate_discard_cmd(dcc, dc);

It seems we need to submit bio first, and then move dc to wait_list, if there's
no error, in __submit_discard_cmd().

> +			}
>  
>  			if (issued >= dpolicy->max_requests)
>  				break;
> -- 
> Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.

Re: [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount

[Jaegeuk Kim]

On 03/12, Sahitya Tummala wrote:
> F2FS already has a default timeout of 5 secs for discards that
> can be issued during umount, but it can take more than the 5 sec
> timeout if the underlying UFS device queue is already full and there
> are no more available free tags to be used. In that case, submit_bio()
> will wait for the already queued discard requests to complete to get
> a free tag, which can potentially take way more than 5 sec.
> 
> Fix this by submitting the discard requests with REQ_NOWAIT
> flags during umount. This will return -EAGAIN for UFS queue/tag full
> scenario without waiting in the context of submit_bio(). The FS can
> then handle these requests by retrying again within the stipulated
> discard timeout period to avoid long latencies.
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> ---
>  fs/f2fs/segment.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index fb3e531..a06bbac 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> +	int flag;
>  	block_t lstart, start, len, total_len;
>  	int err = 0;
>  
> +	flag = dpolicy->sync ? REQ_SYNC : 0;
> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> +
>  	if (dc->state != D_PREP)
>  		return 0;
>  
> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  		bio->bi_end_io = f2fs_submit_discard_endio;
>  		bio->bi_opf |= flag;
>  		submit_bio(bio);
> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> +			dc->state = D_PREP;
> +			err = dc->error;
> +			break;
> +		}
>  
>  		atomic_inc(&dcc->issued_discard);
>  
> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  			}
>  
>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> +			if (dc->error == -EAGAIN) {
> +				congestion_wait(BLK_RW_ASYNC, HZ/50);

						--> need to be DEFAULT_IO_TIMEOUT

> +				__relocate_discard_cmd(dcc, dc);

It seems we need to submit bio first, and then move dc to wait_list, if there's
no error, in __submit_discard_cmd().

> +			}
>  
>  			if (issued >= dpolicy->max_requests)
>  				break;
> -- 
> Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.


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Re: [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

On Thu, Mar 12, 2020 at 10:02:42AM -0700, Jaegeuk Kim wrote:
> On 03/12, Sahitya Tummala wrote:
> > F2FS already has a default timeout of 5 secs for discards that
> > can be issued during umount, but it can take more than the 5 sec
> > timeout if the underlying UFS device queue is already full and there
> > are no more available free tags to be used. In that case, submit_bio()
> > will wait for the already queued discard requests to complete to get
> > a free tag, which can potentially take way more than 5 sec.
> > 
> > Fix this by submitting the discard requests with REQ_NOWAIT
> > flags during umount. This will return -EAGAIN for UFS queue/tag full
> > scenario without waiting in the context of submit_bio(). The FS can
> > then handle these requests by retrying again within the stipulated
> > discard timeout period to avoid long latencies.
> > 
> > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > ---
> >  fs/f2fs/segment.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index fb3e531..a06bbac 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> >  					&(dcc->fstrim_list) : &(dcc->wait_list);
> > -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> > +	int flag;
> >  	block_t lstart, start, len, total_len;
> >  	int err = 0;
> >  
> > +	flag = dpolicy->sync ? REQ_SYNC : 0;
> > +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> > +
> >  	if (dc->state != D_PREP)
> >  		return 0;
> >  
> > @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >  		bio->bi_end_io = f2fs_submit_discard_endio;
> >  		bio->bi_opf |= flag;
> >  		submit_bio(bio);
> > +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> > +			dc->state = D_PREP;
> > +			err = dc->error;
> > +			break;
> > +		}
> >  
> >  		atomic_inc(&dcc->issued_discard);
> >  
> > @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >  			}
> >  
> >  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > +			if (dc->error == -EAGAIN) {
> > +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> 
> 						--> need to be DEFAULT_IO_TIMEOUT

Yes, i will update it.

> 
> > +				__relocate_discard_cmd(dcc, dc);
> 
> It seems we need to submit bio first, and then move dc to wait_list, if there's
> no error, in __submit_discard_cmd().

Yes, that is not changed and it still happens for the failed request
that is re-queued here too when it gets submitted again later.

I am requeuing the discard request failed with -EAGAIN error back to 
dcc->pend_list[] from wait_list. It will call submit_bio() for this request
and also move to wait_list when it calls __submit_discard_cmd() again next
time. Please let me know if I am missing anything?

Thanks,

> 
> > +			}
> >  
> >  			if (issued >= dpolicy->max_requests)
> >  				break;
> > -- 
> > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Jaegeuk Kim]

On 03/13, Sahitya Tummala wrote:
> On Thu, Mar 12, 2020 at 10:02:42AM -0700, Jaegeuk Kim wrote:
> > On 03/12, Sahitya Tummala wrote:
> > > F2FS already has a default timeout of 5 secs for discards that
> > > can be issued during umount, but it can take more than the 5 sec
> > > timeout if the underlying UFS device queue is already full and there
> > > are no more available free tags to be used. In that case, submit_bio()
> > > will wait for the already queued discard requests to complete to get
> > > a free tag, which can potentially take way more than 5 sec.
> > > 
> > > Fix this by submitting the discard requests with REQ_NOWAIT
> > > flags during umount. This will return -EAGAIN for UFS queue/tag full
> > > scenario without waiting in the context of submit_bio(). The FS can
> > > then handle these requests by retrying again within the stipulated
> > > discard timeout period to avoid long latencies.
> > > 
> > > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > > ---
> > >  fs/f2fs/segment.c | 14 +++++++++++++-
> > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > > index fb3e531..a06bbac 100644
> > > --- a/fs/f2fs/segment.c
> > > +++ b/fs/f2fs/segment.c
> > > @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > >  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > >  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> > >  					&(dcc->fstrim_list) : &(dcc->wait_list);
> > > -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> > > +	int flag;
> > >  	block_t lstart, start, len, total_len;
> > >  	int err = 0;
> > >  
> > > +	flag = dpolicy->sync ? REQ_SYNC : 0;
> > > +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> > > +
> > >  	if (dc->state != D_PREP)
> > >  		return 0;
> > >  
> > > @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > >  		bio->bi_end_io = f2fs_submit_discard_endio;
> > >  		bio->bi_opf |= flag;
> > >  		submit_bio(bio);
> > > +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> > > +			dc->state = D_PREP;
> > > +			err = dc->error;
> > > +			break;
> > > +		}
> > >  
> > >  		atomic_inc(&dcc->issued_discard);
> > >  
> > > @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > >  			}
> > >  
> > >  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > > +			if (dc->error == -EAGAIN) {
> > > +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> > 
> > 						--> need to be DEFAULT_IO_TIMEOUT
> 
> Yes, i will update it.
> 
> > 
> > > +				__relocate_discard_cmd(dcc, dc);
> > 
> > It seems we need to submit bio first, and then move dc to wait_list, if there's
> > no error, in __submit_discard_cmd().
> 
> Yes, that is not changed and it still happens for the failed request
> that is re-queued here too when it gets submitted again later.
> 
> I am requeuing the discard request failed with -EAGAIN error back to 
> dcc->pend_list[] from wait_list. It will call submit_bio() for this request
> and also move to wait_list when it calls __submit_discard_cmd() again next
> time. Please let me know if I am missing anything?

This patch has no problem, but I'm thinking that __submit_discard_cmd() needs
to return with any values by assumption where the waiting list should have
submitted commands.

> 
> Thanks,
> 
> > 
> > > +			}
> > >  
> > >  			if (issued >= dpolicy->max_requests)
> > >  				break;
> > > -- 
> > > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> > > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
> 
> -- 
> --
> Sent by a consultant of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount

[Jaegeuk Kim]

On 03/13, Sahitya Tummala wrote:
> On Thu, Mar 12, 2020 at 10:02:42AM -0700, Jaegeuk Kim wrote:
> > On 03/12, Sahitya Tummala wrote:
> > > F2FS already has a default timeout of 5 secs for discards that
> > > can be issued during umount, but it can take more than the 5 sec
> > > timeout if the underlying UFS device queue is already full and there
> > > are no more available free tags to be used. In that case, submit_bio()
> > > will wait for the already queued discard requests to complete to get
> > > a free tag, which can potentially take way more than 5 sec.
> > > 
> > > Fix this by submitting the discard requests with REQ_NOWAIT
> > > flags during umount. This will return -EAGAIN for UFS queue/tag full
> > > scenario without waiting in the context of submit_bio(). The FS can
> > > then handle these requests by retrying again within the stipulated
> > > discard timeout period to avoid long latencies.
> > > 
> > > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > > ---
> > >  fs/f2fs/segment.c | 14 +++++++++++++-
> > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > > index fb3e531..a06bbac 100644
> > > --- a/fs/f2fs/segment.c
> > > +++ b/fs/f2fs/segment.c
> > > @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > >  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > >  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> > >  					&(dcc->fstrim_list) : &(dcc->wait_list);
> > > -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> > > +	int flag;
> > >  	block_t lstart, start, len, total_len;
> > >  	int err = 0;
> > >  
> > > +	flag = dpolicy->sync ? REQ_SYNC : 0;
> > > +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> > > +
> > >  	if (dc->state != D_PREP)
> > >  		return 0;
> > >  
> > > @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > >  		bio->bi_end_io = f2fs_submit_discard_endio;
> > >  		bio->bi_opf |= flag;
> > >  		submit_bio(bio);
> > > +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> > > +			dc->state = D_PREP;
> > > +			err = dc->error;
> > > +			break;
> > > +		}
> > >  
> > >  		atomic_inc(&dcc->issued_discard);
> > >  
> > > @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > >  			}
> > >  
> > >  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > > +			if (dc->error == -EAGAIN) {
> > > +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> > 
> > 						--> need to be DEFAULT_IO_TIMEOUT
> 
> Yes, i will update it.
> 
> > 
> > > +				__relocate_discard_cmd(dcc, dc);
> > 
> > It seems we need to submit bio first, and then move dc to wait_list, if there's
> > no error, in __submit_discard_cmd().
> 
> Yes, that is not changed and it still happens for the failed request
> that is re-queued here too when it gets submitted again later.
> 
> I am requeuing the discard request failed with -EAGAIN error back to 
> dcc->pend_list[] from wait_list. It will call submit_bio() for this request
> and also move to wait_list when it calls __submit_discard_cmd() again next
> time. Please let me know if I am missing anything?

This patch has no problem, but I'm thinking that __submit_discard_cmd() needs
to return with any values by assumption where the waiting list should have
submitted commands.

> 
> Thanks,
> 
> > 
> > > +			}
> > >  
> > >  			if (issued >= dpolicy->max_requests)
> > >  				break;
> > > -- 
> > > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> > > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
> 
> -- 
> --
> Sent by a consultant of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


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Re: [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

On 2020/3/12 19:14, Sahitya Tummala wrote:
> F2FS already has a default timeout of 5 secs for discards that
> can be issued during umount, but it can take more than the 5 sec
> timeout if the underlying UFS device queue is already full and there
> are no more available free tags to be used. In that case, submit_bio()
> will wait for the already queued discard requests to complete to get
> a free tag, which can potentially take way more than 5 sec.
> 
> Fix this by submitting the discard requests with REQ_NOWAIT
> flags during umount. This will return -EAGAIN for UFS queue/tag full
> scenario without waiting in the context of submit_bio(). The FS can
> then handle these requests by retrying again within the stipulated
> discard timeout period to avoid long latencies.
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> ---
>  fs/f2fs/segment.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index fb3e531..a06bbac 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> +	int flag;
>  	block_t lstart, start, len, total_len;
>  	int err = 0;
>  
> +	flag = dpolicy->sync ? REQ_SYNC : 0;
> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> +
>  	if (dc->state != D_PREP)
>  		return 0;
>  
> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  		bio->bi_end_io = f2fs_submit_discard_endio;
>  		bio->bi_opf |= flag;
>  		submit_bio(bio);
> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {

If we want to update dc->state, we need to cover it with dc->lock.

> +			dc->state = D_PREP;

BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
pending list... which is inconsistent status.

Thanks,

> +			err = dc->error;
> +			break;
> +		}
>  
>  		atomic_inc(&dcc->issued_discard);
>  
> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  			}
>  
>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> +			if (dc->error == -EAGAIN) {
> +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> +				__relocate_discard_cmd(dcc, dc);
> +			}
>  
>  			if (issued >= dpolicy->max_requests)
>  				break;
> 

Re: [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

On 2020/3/12 19:14, Sahitya Tummala wrote:
> F2FS already has a default timeout of 5 secs for discards that
> can be issued during umount, but it can take more than the 5 sec
> timeout if the underlying UFS device queue is already full and there
> are no more available free tags to be used. In that case, submit_bio()
> will wait for the already queued discard requests to complete to get
> a free tag, which can potentially take way more than 5 sec.
> 
> Fix this by submitting the discard requests with REQ_NOWAIT
> flags during umount. This will return -EAGAIN for UFS queue/tag full
> scenario without waiting in the context of submit_bio(). The FS can
> then handle these requests by retrying again within the stipulated
> discard timeout period to avoid long latencies.
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> ---
>  fs/f2fs/segment.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index fb3e531..a06bbac 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> +	int flag;
>  	block_t lstart, start, len, total_len;
>  	int err = 0;
>  
> +	flag = dpolicy->sync ? REQ_SYNC : 0;
> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> +
>  	if (dc->state != D_PREP)
>  		return 0;
>  
> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  		bio->bi_end_io = f2fs_submit_discard_endio;
>  		bio->bi_opf |= flag;
>  		submit_bio(bio);
> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {

If we want to update dc->state, we need to cover it with dc->lock.

> +			dc->state = D_PREP;

BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
pending list... which is inconsistent status.

Thanks,

> +			err = dc->error;
> +			break;
> +		}
>  
>  		atomic_inc(&dcc->issued_discard);
>  
> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  			}
>  
>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> +			if (dc->error == -EAGAIN) {
> +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> +				__relocate_discard_cmd(dcc, dc);
> +			}
>  
>  			if (issued >= dpolicy->max_requests)
>  				break;
> 


_______________________________________________
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Re: [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote:
> On 2020/3/12 19:14, Sahitya Tummala wrote:
> > F2FS already has a default timeout of 5 secs for discards that
> > can be issued during umount, but it can take more than the 5 sec
> > timeout if the underlying UFS device queue is already full and there
> > are no more available free tags to be used. In that case, submit_bio()
> > will wait for the already queued discard requests to complete to get
> > a free tag, which can potentially take way more than 5 sec.
> > 
> > Fix this by submitting the discard requests with REQ_NOWAIT
> > flags during umount. This will return -EAGAIN for UFS queue/tag full
> > scenario without waiting in the context of submit_bio(). The FS can
> > then handle these requests by retrying again within the stipulated
> > discard timeout period to avoid long latencies.
> > 
> > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > ---
> >  fs/f2fs/segment.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index fb3e531..a06bbac 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> >  					&(dcc->fstrim_list) : &(dcc->wait_list);
> > -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> > +	int flag;
> >  	block_t lstart, start, len, total_len;
> >  	int err = 0;
> >  
> > +	flag = dpolicy->sync ? REQ_SYNC : 0;
> > +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> > +
> >  	if (dc->state != D_PREP)
> >  		return 0;
> >  
> > @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >  		bio->bi_end_io = f2fs_submit_discard_endio;
> >  		bio->bi_opf |= flag;
> >  		submit_bio(bio);
> > +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> 
> If we want to update dc->state, we need to cover it with dc->lock.

Sure, will update it.

> 
> > +			dc->state = D_PREP;
> 
> BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
> D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
> pending list... which is inconsistent status.

In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state
will not be updated to D_DONE in f2fs_submit_discard_endio()?

Thanks,

> 
> Thanks,
> 
> > +			err = dc->error;
> > +			break;
> > +		}
> >  
> >  		atomic_inc(&dcc->issued_discard);
> >  
> > @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >  			}
> >  
> >  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > +			if (dc->error == -EAGAIN) {
> > +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> > +				__relocate_discard_cmd(dcc, dc);
> > +			}
> >  
> >  			if (issued >= dpolicy->max_requests)
> >  				break;
> > 

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

On Thu, Mar 12, 2020 at 06:45:35PM -0700, Jaegeuk Kim wrote:
> On 03/13, Sahitya Tummala wrote:
> > On Thu, Mar 12, 2020 at 10:02:42AM -0700, Jaegeuk Kim wrote:
> > > On 03/12, Sahitya Tummala wrote:
> > > > F2FS already has a default timeout of 5 secs for discards that
> > > > can be issued during umount, but it can take more than the 5 sec
> > > > timeout if the underlying UFS device queue is already full and there
> > > > are no more available free tags to be used. In that case, submit_bio()
> > > > will wait for the already queued discard requests to complete to get
> > > > a free tag, which can potentially take way more than 5 sec.
> > > > 
> > > > Fix this by submitting the discard requests with REQ_NOWAIT
> > > > flags during umount. This will return -EAGAIN for UFS queue/tag full
> > > > scenario without waiting in the context of submit_bio(). The FS can
> > > > then handle these requests by retrying again within the stipulated
> > > > discard timeout period to avoid long latencies.
> > > > 
> > > > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > > > ---
> > > >  fs/f2fs/segment.c | 14 +++++++++++++-
> > > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > > > index fb3e531..a06bbac 100644
> > > > --- a/fs/f2fs/segment.c
> > > > +++ b/fs/f2fs/segment.c
> > > > @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > > >  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > > >  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> > > >  					&(dcc->fstrim_list) : &(dcc->wait_list);
> > > > -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> > > > +	int flag;
> > > >  	block_t lstart, start, len, total_len;
> > > >  	int err = 0;
> > > >  
> > > > +	flag = dpolicy->sync ? REQ_SYNC : 0;
> > > > +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> > > > +
> > > >  	if (dc->state != D_PREP)
> > > >  		return 0;
> > > >  
> > > > @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > > >  		bio->bi_end_io = f2fs_submit_discard_endio;
> > > >  		bio->bi_opf |= flag;
> > > >  		submit_bio(bio);
> > > > +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> > > > +			dc->state = D_PREP;
> > > > +			err = dc->error;
> > > > +			break;
> > > > +		}
> > > >  
> > > >  		atomic_inc(&dcc->issued_discard);
> > > >  
> > > > @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > > >  			}
> > > >  
> > > >  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > > > +			if (dc->error == -EAGAIN) {
> > > > +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> > > 
> > > 						--> need to be DEFAULT_IO_TIMEOUT
> > 
> > Yes, i will update it.
> > 
> > > 
> > > > +				__relocate_discard_cmd(dcc, dc);
> > > 
> > > It seems we need to submit bio first, and then move dc to wait_list, if there's
> > > no error, in __submit_discard_cmd().
> > 
> > Yes, that is not changed and it still happens for the failed request
> > that is re-queued here too when it gets submitted again later.
> > 
> > I am requeuing the discard request failed with -EAGAIN error back to 
> > dcc->pend_list[] from wait_list. It will call submit_bio() for this request
> > and also move to wait_list when it calls __submit_discard_cmd() again next
> > time. Please let me know if I am missing anything?
> 
> This patch has no problem, but I'm thinking that __submit_discard_cmd() needs
> to return with any values by assumption where the waiting list should have
> submitted commands.

I think dc->queued will indicated that dc is moved to wait_list. This can be
used along with return value to take right action. Can you check if this
works?

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index a06bbac..91df060 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1478,7 +1478,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
        struct list_head *pend_list;
        struct discard_cmd *dc, *tmp;
        struct blk_plug plug;
-       int i, issued = 0;
+       int i, err, issued = 0;
        bool io_interrupted = false;

        if (dpolicy->timeout != 0)
@@ -1517,8 +1517,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
                                break;
                        }

-                       __submit_discard_cmd(sbi, dpolicy, dc, &issued);
-                       if (dc->error == -EAGAIN) {
+                       err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
+                       if (err && err != -EAGAIN) {
+                               __remove_discard_cmd(sbi, dc);
+                       } else if (err == -EAGAIN && dc->queued) {
                                congestion_wait(BLK_RW_ASYNC, HZ/50);
                                __relocate_discard_cmd(dcc, dc);
                        }

thanks,
> 
> > 
> > Thanks,
> > 
> > > 
> > > > +			}
> > > >  
> > > >  			if (issued >= dpolicy->max_requests)
> > > >  				break;
> > > > -- 
> > > > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> > > > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
> > 
> > -- 
> > --
> > Sent by a consultant of the Qualcomm Innovation Center, Inc.
> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

On Thu, Mar 12, 2020 at 06:45:35PM -0700, Jaegeuk Kim wrote:
> On 03/13, Sahitya Tummala wrote:
> > On Thu, Mar 12, 2020 at 10:02:42AM -0700, Jaegeuk Kim wrote:
> > > On 03/12, Sahitya Tummala wrote:
> > > > F2FS already has a default timeout of 5 secs for discards that
> > > > can be issued during umount, but it can take more than the 5 sec
> > > > timeout if the underlying UFS device queue is already full and there
> > > > are no more available free tags to be used. In that case, submit_bio()
> > > > will wait for the already queued discard requests to complete to get
> > > > a free tag, which can potentially take way more than 5 sec.
> > > > 
> > > > Fix this by submitting the discard requests with REQ_NOWAIT
> > > > flags during umount. This will return -EAGAIN for UFS queue/tag full
> > > > scenario without waiting in the context of submit_bio(). The FS can
> > > > then handle these requests by retrying again within the stipulated
> > > > discard timeout period to avoid long latencies.
> > > > 
> > > > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > > > ---
> > > >  fs/f2fs/segment.c | 14 +++++++++++++-
> > > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > > > index fb3e531..a06bbac 100644
> > > > --- a/fs/f2fs/segment.c
> > > > +++ b/fs/f2fs/segment.c
> > > > @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > > >  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > > >  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> > > >  					&(dcc->fstrim_list) : &(dcc->wait_list);
> > > > -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> > > > +	int flag;
> > > >  	block_t lstart, start, len, total_len;
> > > >  	int err = 0;
> > > >  
> > > > +	flag = dpolicy->sync ? REQ_SYNC : 0;
> > > > +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> > > > +
> > > >  	if (dc->state != D_PREP)
> > > >  		return 0;
> > > >  
> > > > @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > > >  		bio->bi_end_io = f2fs_submit_discard_endio;
> > > >  		bio->bi_opf |= flag;
> > > >  		submit_bio(bio);
> > > > +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> > > > +			dc->state = D_PREP;
> > > > +			err = dc->error;
> > > > +			break;
> > > > +		}
> > > >  
> > > >  		atomic_inc(&dcc->issued_discard);
> > > >  
> > > > @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > > >  			}
> > > >  
> > > >  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > > > +			if (dc->error == -EAGAIN) {
> > > > +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> > > 
> > > 						--> need to be DEFAULT_IO_TIMEOUT
> > 
> > Yes, i will update it.
> > 
> > > 
> > > > +				__relocate_discard_cmd(dcc, dc);
> > > 
> > > It seems we need to submit bio first, and then move dc to wait_list, if there's
> > > no error, in __submit_discard_cmd().
> > 
> > Yes, that is not changed and it still happens for the failed request
> > that is re-queued here too when it gets submitted again later.
> > 
> > I am requeuing the discard request failed with -EAGAIN error back to 
> > dcc->pend_list[] from wait_list. It will call submit_bio() for this request
> > and also move to wait_list when it calls __submit_discard_cmd() again next
> > time. Please let me know if I am missing anything?
> 
> This patch has no problem, but I'm thinking that __submit_discard_cmd() needs
> to return with any values by assumption where the waiting list should have
> submitted commands.

I think dc->queued will indicated that dc is moved to wait_list. This can be
used along with return value to take right action. Can you check if this
works?

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index a06bbac..91df060 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1478,7 +1478,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
        struct list_head *pend_list;
        struct discard_cmd *dc, *tmp;
        struct blk_plug plug;
-       int i, issued = 0;
+       int i, err, issued = 0;
        bool io_interrupted = false;

        if (dpolicy->timeout != 0)
@@ -1517,8 +1517,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
                                break;
                        }

-                       __submit_discard_cmd(sbi, dpolicy, dc, &issued);
-                       if (dc->error == -EAGAIN) {
+                       err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
+                       if (err && err != -EAGAIN) {
+                               __remove_discard_cmd(sbi, dc);
+                       } else if (err == -EAGAIN && dc->queued) {
                                congestion_wait(BLK_RW_ASYNC, HZ/50);
                                __relocate_discard_cmd(dcc, dc);
                        }

thanks,
> 
> > 
> > Thanks,
> > 
> > > 
> > > > +			}
> > > >  
> > > >  			if (issued >= dpolicy->max_requests)
> > > >  				break;
> > > > -- 
> > > > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> > > > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
> > 
> > -- 
> > --
> > Sent by a consultant of the Qualcomm Innovation Center, Inc.
> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


_______________________________________________
Linux-f2fs-devel mailing list
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Re: [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

On 2020/3/13 11:39, Sahitya Tummala wrote:
> On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote:
>> On 2020/3/12 19:14, Sahitya Tummala wrote:
>>> F2FS already has a default timeout of 5 secs for discards that
>>> can be issued during umount, but it can take more than the 5 sec
>>> timeout if the underlying UFS device queue is already full and there
>>> are no more available free tags to be used. In that case, submit_bio()
>>> will wait for the already queued discard requests to complete to get
>>> a free tag, which can potentially take way more than 5 sec.
>>>
>>> Fix this by submitting the discard requests with REQ_NOWAIT
>>> flags during umount. This will return -EAGAIN for UFS queue/tag full
>>> scenario without waiting in the context of submit_bio(). The FS can
>>> then handle these requests by retrying again within the stipulated
>>> discard timeout period to avoid long latencies.
>>>
>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
>>> ---
>>>  fs/f2fs/segment.c | 14 +++++++++++++-
>>>  1 file changed, 13 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index fb3e531..a06bbac 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>>>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>>>  					&(dcc->fstrim_list) : &(dcc->wait_list);
>>> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
>>> +	int flag;
>>>  	block_t lstart, start, len, total_len;
>>>  	int err = 0;
>>>  
>>> +	flag = dpolicy->sync ? REQ_SYNC : 0;
>>> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
>>> +
>>>  	if (dc->state != D_PREP)
>>>  		return 0;
>>>  
>>> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>  		bio->bi_end_io = f2fs_submit_discard_endio;
>>>  		bio->bi_opf |= flag;
>>>  		submit_bio(bio);
>>> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
>>
>> If we want to update dc->state, we need to cover it with dc->lock.
> 
> Sure, will update it.
> 
>>
>>> +			dc->state = D_PREP;
>>
>> BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
>> D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
>> pending list... which is inconsistent status.
> 
> In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state
> will not be updated to D_DONE in f2fs_submit_discard_endio()?

__submit_discard_cmd()
 lock()
 dc->state = D_SUBMIT;
 dc->bio_ref++;
 unlock()
...
 submit_bio()
				f2fs_submit_discard_endio()
				 dc->error = -EAGAIN;
				 lock()
				 dc->bio_ref--;

 dc->state = D_PREP;

				 dc->state = D_DONE;
				 unlock()

So finally, dc's state is D_DONE, and it's in wait list, then will be relocated
to pending list.

> 
> Thanks,
> 
>>
>> Thanks,
>>
>>> +			err = dc->error;
>>> +			break;
>>> +		}
>>>  
>>>  		atomic_inc(&dcc->issued_discard);
>>>  
>>> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>  			}
>>>  
>>>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
>>> +			if (dc->error == -EAGAIN) {
>>> +				congestion_wait(BLK_RW_ASYNC, HZ/50);
>>> +				__relocate_discard_cmd(dcc, dc);
>>> +			}
>>>  
>>>  			if (issued >= dpolicy->max_requests)
>>>  				break;
>>>
> 

Re: [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

On 2020/3/13 11:39, Sahitya Tummala wrote:
> On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote:
>> On 2020/3/12 19:14, Sahitya Tummala wrote:
>>> F2FS already has a default timeout of 5 secs for discards that
>>> can be issued during umount, but it can take more than the 5 sec
>>> timeout if the underlying UFS device queue is already full and there
>>> are no more available free tags to be used. In that case, submit_bio()
>>> will wait for the already queued discard requests to complete to get
>>> a free tag, which can potentially take way more than 5 sec.
>>>
>>> Fix this by submitting the discard requests with REQ_NOWAIT
>>> flags during umount. This will return -EAGAIN for UFS queue/tag full
>>> scenario without waiting in the context of submit_bio(). The FS can
>>> then handle these requests by retrying again within the stipulated
>>> discard timeout period to avoid long latencies.
>>>
>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
>>> ---
>>>  fs/f2fs/segment.c | 14 +++++++++++++-
>>>  1 file changed, 13 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index fb3e531..a06bbac 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>>>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>>>  					&(dcc->fstrim_list) : &(dcc->wait_list);
>>> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
>>> +	int flag;
>>>  	block_t lstart, start, len, total_len;
>>>  	int err = 0;
>>>  
>>> +	flag = dpolicy->sync ? REQ_SYNC : 0;
>>> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
>>> +
>>>  	if (dc->state != D_PREP)
>>>  		return 0;
>>>  
>>> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>  		bio->bi_end_io = f2fs_submit_discard_endio;
>>>  		bio->bi_opf |= flag;
>>>  		submit_bio(bio);
>>> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
>>
>> If we want to update dc->state, we need to cover it with dc->lock.
> 
> Sure, will update it.
> 
>>
>>> +			dc->state = D_PREP;
>>
>> BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
>> D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
>> pending list... which is inconsistent status.
> 
> In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state
> will not be updated to D_DONE in f2fs_submit_discard_endio()?

__submit_discard_cmd()
 lock()
 dc->state = D_SUBMIT;
 dc->bio_ref++;
 unlock()
...
 submit_bio()
				f2fs_submit_discard_endio()
				 dc->error = -EAGAIN;
				 lock()
				 dc->bio_ref--;

 dc->state = D_PREP;

				 dc->state = D_DONE;
				 unlock()

So finally, dc's state is D_DONE, and it's in wait list, then will be relocated
to pending list.

> 
> Thanks,
> 
>>
>> Thanks,
>>
>>> +			err = dc->error;
>>> +			break;
>>> +		}
>>>  
>>>  		atomic_inc(&dcc->issued_discard);
>>>  
>>> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>  			}
>>>  
>>>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
>>> +			if (dc->error == -EAGAIN) {
>>> +				congestion_wait(BLK_RW_ASYNC, HZ/50);
>>> +				__relocate_discard_cmd(dcc, dc);
>>> +			}
>>>  
>>>  			if (issued >= dpolicy->max_requests)
>>>  				break;
>>>
> 


_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

On Fri, Mar 13, 2020 at 02:30:55PM +0800, Chao Yu wrote:
> On 2020/3/13 11:39, Sahitya Tummala wrote:
> > On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote:
> >> On 2020/3/12 19:14, Sahitya Tummala wrote:
> >>> F2FS already has a default timeout of 5 secs for discards that
> >>> can be issued during umount, but it can take more than the 5 sec
> >>> timeout if the underlying UFS device queue is already full and there
> >>> are no more available free tags to be used. In that case, submit_bio()
> >>> will wait for the already queued discard requests to complete to get
> >>> a free tag, which can potentially take way more than 5 sec.
> >>>
> >>> Fix this by submitting the discard requests with REQ_NOWAIT
> >>> flags during umount. This will return -EAGAIN for UFS queue/tag full
> >>> scenario without waiting in the context of submit_bio(). The FS can
> >>> then handle these requests by retrying again within the stipulated
> >>> discard timeout period to avoid long latencies.
> >>>
> >>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> >>> ---
> >>>  fs/f2fs/segment.c | 14 +++++++++++++-
> >>>  1 file changed, 13 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>> index fb3e531..a06bbac 100644
> >>> --- a/fs/f2fs/segment.c
> >>> +++ b/fs/f2fs/segment.c
> >>> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> >>>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> >>> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> >>> +	int flag;
> >>>  	block_t lstart, start, len, total_len;
> >>>  	int err = 0;
> >>>  
> >>> +	flag = dpolicy->sync ? REQ_SYNC : 0;
> >>> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> >>> +
> >>>  	if (dc->state != D_PREP)
> >>>  		return 0;
> >>>  
> >>> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  		bio->bi_end_io = f2fs_submit_discard_endio;
> >>>  		bio->bi_opf |= flag;
> >>>  		submit_bio(bio);
> >>> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> >>
> >> If we want to update dc->state, we need to cover it with dc->lock.
> > 
> > Sure, will update it.
> > 
> >>
> >>> +			dc->state = D_PREP;
> >>
> >> BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
> >> D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
> >> pending list... which is inconsistent status.
> > 
> > In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state
> > will not be updated to D_DONE in f2fs_submit_discard_endio()?
> 
> __submit_discard_cmd()
>  lock()
>  dc->state = D_SUBMIT;
>  dc->bio_ref++;
>  unlock()
> ...
>  submit_bio()
> 				f2fs_submit_discard_endio()
> 				 dc->error = -EAGAIN;
> 				 lock()
> 				 dc->bio_ref--;
> 
>  dc->state = D_PREP;
> 
> 				 dc->state = D_DONE;
> 				 unlock()
> 
> So finally, dc's state is D_DONE, and it's in wait list, then will be relocated
> to pending list.

In case of queue full, f2fs_submit_discard_endio() will not be called
asynchronously. It will be called in the context of submit_bio() itself.
So by the time, submit_bio returns dc->error will be -EAGAIN and dc->state
will be D_DONE. 

submit_bio()
->blk_mq_make_request
->blk_mq_get_request()
  ->bio_wouldblock_error() (called due to queue full)
    ->bio_endio()
    
Thanks,
> 
> > 
> > Thanks,
> > 
> >>
> >> Thanks,
> >>
> >>> +			err = dc->error;
> >>> +			break;
> >>> +		}
> >>>  
> >>>  		atomic_inc(&dcc->issued_discard);
> >>>  
> >>> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  			}
> >>>  
> >>>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> >>> +			if (dc->error == -EAGAIN) {
> >>> +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> >>> +				__relocate_discard_cmd(dcc, dc);
> >>> +			}
> >>>  
> >>>  			if (issued >= dpolicy->max_requests)
> >>>  				break;
> >>>
> > 

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Jaegeuk Kim]

On 03/13, Sahitya Tummala wrote:
> On Thu, Mar 12, 2020 at 06:45:35PM -0700, Jaegeuk Kim wrote:
> > On 03/13, Sahitya Tummala wrote:
> > > On Thu, Mar 12, 2020 at 10:02:42AM -0700, Jaegeuk Kim wrote:
> > > > On 03/12, Sahitya Tummala wrote:
> > > > > F2FS already has a default timeout of 5 secs for discards that
> > > > > can be issued during umount, but it can take more than the 5 sec
> > > > > timeout if the underlying UFS device queue is already full and there
> > > > > are no more available free tags to be used. In that case, submit_bio()
> > > > > will wait for the already queued discard requests to complete to get
> > > > > a free tag, which can potentially take way more than 5 sec.
> > > > > 
> > > > > Fix this by submitting the discard requests with REQ_NOWAIT
> > > > > flags during umount. This will return -EAGAIN for UFS queue/tag full
> > > > > scenario without waiting in the context of submit_bio(). The FS can
> > > > > then handle these requests by retrying again within the stipulated
> > > > > discard timeout period to avoid long latencies.
> > > > > 
> > > > > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > > > > ---
> > > > >  fs/f2fs/segment.c | 14 +++++++++++++-
> > > > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > > > > index fb3e531..a06bbac 100644
> > > > > --- a/fs/f2fs/segment.c
> > > > > +++ b/fs/f2fs/segment.c
> > > > > @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > > > >  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > > > >  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> > > > >  					&(dcc->fstrim_list) : &(dcc->wait_list);
> > > > > -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> > > > > +	int flag;
> > > > >  	block_t lstart, start, len, total_len;
> > > > >  	int err = 0;
> > > > >  
> > > > > +	flag = dpolicy->sync ? REQ_SYNC : 0;
> > > > > +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> > > > > +
> > > > >  	if (dc->state != D_PREP)
> > > > >  		return 0;
> > > > >  
> > > > > @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > > > >  		bio->bi_end_io = f2fs_submit_discard_endio;
> > > > >  		bio->bi_opf |= flag;
> > > > >  		submit_bio(bio);
> > > > > +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> > > > > +			dc->state = D_PREP;
> > > > > +			err = dc->error;
> > > > > +			break;
> > > > > +		}
> > > > >  
> > > > >  		atomic_inc(&dcc->issued_discard);
> > > > >  
> > > > > @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > > > >  			}
> > > > >  
> > > > >  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > > > > +			if (dc->error == -EAGAIN) {
> > > > > +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> > > > 
> > > > 						--> need to be DEFAULT_IO_TIMEOUT
> > > 
> > > Yes, i will update it.
> > > 
> > > > 
> > > > > +				__relocate_discard_cmd(dcc, dc);
> > > > 
> > > > It seems we need to submit bio first, and then move dc to wait_list, if there's
> > > > no error, in __submit_discard_cmd().
> > > 
> > > Yes, that is not changed and it still happens for the failed request
> > > that is re-queued here too when it gets submitted again later.
> > > 
> > > I am requeuing the discard request failed with -EAGAIN error back to 
> > > dcc->pend_list[] from wait_list. It will call submit_bio() for this request
> > > and also move to wait_list when it calls __submit_discard_cmd() again next
> > > time. Please let me know if I am missing anything?
> > 
> > This patch has no problem, but I'm thinking that __submit_discard_cmd() needs
> > to return with any values by assumption where the waiting list should have
> > submitted commands.
> 
> I think dc->queued will indicated that dc is moved to wait_list. This can be
> used along with return value to take right action. Can you check if this
> works?

I mean why can't do this *in* __submit_discard_cmd()? Otherwise, existing and
future callers should consider to handle the errors everytime.

> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index a06bbac..91df060 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1478,7 +1478,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>         struct list_head *pend_list;
>         struct discard_cmd *dc, *tmp;
>         struct blk_plug plug;
> -       int i, issued = 0;
> +       int i, err, issued = 0;
>         bool io_interrupted = false;
> 
>         if (dpolicy->timeout != 0)
> @@ -1517,8 +1517,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>                                 break;
>                         }
> 
> -                       __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> -                       if (dc->error == -EAGAIN) {
> +                       err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> +                       if (err && err != -EAGAIN) {
> +                               __remove_discard_cmd(sbi, dc);
> +                       } else if (err == -EAGAIN && dc->queued) {
>                                 congestion_wait(BLK_RW_ASYNC, HZ/50);
>                                 __relocate_discard_cmd(dcc, dc);
>                         }
> 
> thanks,
> > 
> > > 
> > > Thanks,
> > > 
> > > > 
> > > > > +			}
> > > > >  
> > > > >  			if (issued >= dpolicy->max_requests)
> > > > >  				break;
> > > > > -- 
> > > > > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> > > > > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
> > > 
> > > -- 
> > > --
> > > Sent by a consultant of the Qualcomm Innovation Center, Inc.
> > > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
> 
> -- 
> --
> Sent by a consultant of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount

[Jaegeuk Kim]

On 03/13, Sahitya Tummala wrote:
> On Thu, Mar 12, 2020 at 06:45:35PM -0700, Jaegeuk Kim wrote:
> > On 03/13, Sahitya Tummala wrote:
> > > On Thu, Mar 12, 2020 at 10:02:42AM -0700, Jaegeuk Kim wrote:
> > > > On 03/12, Sahitya Tummala wrote:
> > > > > F2FS already has a default timeout of 5 secs for discards that
> > > > > can be issued during umount, but it can take more than the 5 sec
> > > > > timeout if the underlying UFS device queue is already full and there
> > > > > are no more available free tags to be used. In that case, submit_bio()
> > > > > will wait for the already queued discard requests to complete to get
> > > > > a free tag, which can potentially take way more than 5 sec.
> > > > > 
> > > > > Fix this by submitting the discard requests with REQ_NOWAIT
> > > > > flags during umount. This will return -EAGAIN for UFS queue/tag full
> > > > > scenario without waiting in the context of submit_bio(). The FS can
> > > > > then handle these requests by retrying again within the stipulated
> > > > > discard timeout period to avoid long latencies.
> > > > > 
> > > > > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > > > > ---
> > > > >  fs/f2fs/segment.c | 14 +++++++++++++-
> > > > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > > > > index fb3e531..a06bbac 100644
> > > > > --- a/fs/f2fs/segment.c
> > > > > +++ b/fs/f2fs/segment.c
> > > > > @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > > > >  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > > > >  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> > > > >  					&(dcc->fstrim_list) : &(dcc->wait_list);
> > > > > -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> > > > > +	int flag;
> > > > >  	block_t lstart, start, len, total_len;
> > > > >  	int err = 0;
> > > > >  
> > > > > +	flag = dpolicy->sync ? REQ_SYNC : 0;
> > > > > +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> > > > > +
> > > > >  	if (dc->state != D_PREP)
> > > > >  		return 0;
> > > > >  
> > > > > @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> > > > >  		bio->bi_end_io = f2fs_submit_discard_endio;
> > > > >  		bio->bi_opf |= flag;
> > > > >  		submit_bio(bio);
> > > > > +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> > > > > +			dc->state = D_PREP;
> > > > > +			err = dc->error;
> > > > > +			break;
> > > > > +		}
> > > > >  
> > > > >  		atomic_inc(&dcc->issued_discard);
> > > > >  
> > > > > @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > > > >  			}
> > > > >  
> > > > >  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > > > > +			if (dc->error == -EAGAIN) {
> > > > > +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> > > > 
> > > > 						--> need to be DEFAULT_IO_TIMEOUT
> > > 
> > > Yes, i will update it.
> > > 
> > > > 
> > > > > +				__relocate_discard_cmd(dcc, dc);
> > > > 
> > > > It seems we need to submit bio first, and then move dc to wait_list, if there's
> > > > no error, in __submit_discard_cmd().
> > > 
> > > Yes, that is not changed and it still happens for the failed request
> > > that is re-queued here too when it gets submitted again later.
> > > 
> > > I am requeuing the discard request failed with -EAGAIN error back to 
> > > dcc->pend_list[] from wait_list. It will call submit_bio() for this request
> > > and also move to wait_list when it calls __submit_discard_cmd() again next
> > > time. Please let me know if I am missing anything?
> > 
> > This patch has no problem, but I'm thinking that __submit_discard_cmd() needs
> > to return with any values by assumption where the waiting list should have
> > submitted commands.
> 
> I think dc->queued will indicated that dc is moved to wait_list. This can be
> used along with return value to take right action. Can you check if this
> works?

I mean why can't do this *in* __submit_discard_cmd()? Otherwise, existing and
future callers should consider to handle the errors everytime.

> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index a06bbac..91df060 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1478,7 +1478,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>         struct list_head *pend_list;
>         struct discard_cmd *dc, *tmp;
>         struct blk_plug plug;
> -       int i, issued = 0;
> +       int i, err, issued = 0;
>         bool io_interrupted = false;
> 
>         if (dpolicy->timeout != 0)
> @@ -1517,8 +1517,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>                                 break;
>                         }
> 
> -                       __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> -                       if (dc->error == -EAGAIN) {
> +                       err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> +                       if (err && err != -EAGAIN) {
> +                               __remove_discard_cmd(sbi, dc);
> +                       } else if (err == -EAGAIN && dc->queued) {
>                                 congestion_wait(BLK_RW_ASYNC, HZ/50);
>                                 __relocate_discard_cmd(dcc, dc);
>                         }
> 
> thanks,
> > 
> > > 
> > > Thanks,
> > > 
> > > > 
> > > > > +			}
> > > > >  
> > > > >  			if (issued >= dpolicy->max_requests)
> > > > >  				break;
> > > > > -- 
> > > > > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> > > > > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
> > > 
> > > -- 
> > > --
> > > Sent by a consultant of the Qualcomm Innovation Center, Inc.
> > > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
> 
> -- 
> --
> Sent by a consultant of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


_______________________________________________
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Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

On 2020/3/13 19:08, Sahitya Tummala wrote:
> On Fri, Mar 13, 2020 at 02:30:55PM +0800, Chao Yu wrote:
>> On 2020/3/13 11:39, Sahitya Tummala wrote:
>>> On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote:
>>>> On 2020/3/12 19:14, Sahitya Tummala wrote:
>>>>> F2FS already has a default timeout of 5 secs for discards that
>>>>> can be issued during umount, but it can take more than the 5 sec
>>>>> timeout if the underlying UFS device queue is already full and there
>>>>> are no more available free tags to be used. In that case, submit_bio()
>>>>> will wait for the already queued discard requests to complete to get
>>>>> a free tag, which can potentially take way more than 5 sec.
>>>>>
>>>>> Fix this by submitting the discard requests with REQ_NOWAIT
>>>>> flags during umount. This will return -EAGAIN for UFS queue/tag full
>>>>> scenario without waiting in the context of submit_bio(). The FS can
>>>>> then handle these requests by retrying again within the stipulated
>>>>> discard timeout period to avoid long latencies.
>>>>>
>>>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
>>>>> ---
>>>>>  fs/f2fs/segment.c | 14 +++++++++++++-
>>>>>  1 file changed, 13 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>>> index fb3e531..a06bbac 100644
>>>>> --- a/fs/f2fs/segment.c
>>>>> +++ b/fs/f2fs/segment.c
>>>>> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>>>>>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>>>>>  					&(dcc->fstrim_list) : &(dcc->wait_list);
>>>>> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
>>>>> +	int flag;
>>>>>  	block_t lstart, start, len, total_len;
>>>>>  	int err = 0;
>>>>>  
>>>>> +	flag = dpolicy->sync ? REQ_SYNC : 0;
>>>>> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
>>>>> +
>>>>>  	if (dc->state != D_PREP)
>>>>>  		return 0;
>>>>>  
>>>>> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>  		bio->bi_end_io = f2fs_submit_discard_endio;
>>>>>  		bio->bi_opf |= flag;
>>>>>  		submit_bio(bio);
>>>>> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
>>>>
>>>> If we want to update dc->state, we need to cover it with dc->lock.
>>>
>>> Sure, will update it.
>>>
>>>>
>>>>> +			dc->state = D_PREP;
>>>>
>>>> BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
>>>> D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
>>>> pending list... which is inconsistent status.
>>>
>>> In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state
>>> will not be updated to D_DONE in f2fs_submit_discard_endio()?
>>
>> __submit_discard_cmd()
>>  lock()
>>  dc->state = D_SUBMIT;
>>  dc->bio_ref++;
>>  unlock()
>> ...
>>  submit_bio()
>> 				f2fs_submit_discard_endio()
>> 				 dc->error = -EAGAIN;
>> 				 lock()
>> 				 dc->bio_ref--;
>>
>>  dc->state = D_PREP;
>>
>> 				 dc->state = D_DONE;
>> 				 unlock()
>>
>> So finally, dc's state is D_DONE, and it's in wait list, then will be relocated
>> to pending list.
> 
> In case of queue full, f2fs_submit_discard_endio() will not be called

I guess the case is there are multiple bios related to one dc and partially callback
of bio is called asynchronously and the other is called synchronously, so the race
condition could happen.

Thanks,

> asynchronously. It will be called in the context of submit_bio() itself.
> So by the time, submit_bio returns dc->error will be -EAGAIN and dc->state
> will be D_DONE. 
> 
> submit_bio()
> ->blk_mq_make_request
> ->blk_mq_get_request()
>   ->bio_wouldblock_error() (called due to queue full)
>     ->bio_endio()
>     
> Thanks,
>>
>>>
>>> Thanks,
>>>
>>>>
>>>> Thanks,
>>>>
>>>>> +			err = dc->error;
>>>>> +			break;
>>>>> +		}
>>>>>  
>>>>>  		atomic_inc(&dcc->issued_discard);
>>>>>  
>>>>> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>  			}
>>>>>  
>>>>>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
>>>>> +			if (dc->error == -EAGAIN) {
>>>>> +				congestion_wait(BLK_RW_ASYNC, HZ/50);
>>>>> +				__relocate_discard_cmd(dcc, dc);
>>>>> +			}
>>>>>  
>>>>>  			if (issued >= dpolicy->max_requests)
>>>>>  				break;
>>>>>
>>>
> 

Re: [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

On 2020/3/13 19:08, Sahitya Tummala wrote:
> On Fri, Mar 13, 2020 at 02:30:55PM +0800, Chao Yu wrote:
>> On 2020/3/13 11:39, Sahitya Tummala wrote:
>>> On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote:
>>>> On 2020/3/12 19:14, Sahitya Tummala wrote:
>>>>> F2FS already has a default timeout of 5 secs for discards that
>>>>> can be issued during umount, but it can take more than the 5 sec
>>>>> timeout if the underlying UFS device queue is already full and there
>>>>> are no more available free tags to be used. In that case, submit_bio()
>>>>> will wait for the already queued discard requests to complete to get
>>>>> a free tag, which can potentially take way more than 5 sec.
>>>>>
>>>>> Fix this by submitting the discard requests with REQ_NOWAIT
>>>>> flags during umount. This will return -EAGAIN for UFS queue/tag full
>>>>> scenario without waiting in the context of submit_bio(). The FS can
>>>>> then handle these requests by retrying again within the stipulated
>>>>> discard timeout period to avoid long latencies.
>>>>>
>>>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
>>>>> ---
>>>>>  fs/f2fs/segment.c | 14 +++++++++++++-
>>>>>  1 file changed, 13 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>>> index fb3e531..a06bbac 100644
>>>>> --- a/fs/f2fs/segment.c
>>>>> +++ b/fs/f2fs/segment.c
>>>>> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>>>>>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>>>>>  					&(dcc->fstrim_list) : &(dcc->wait_list);
>>>>> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
>>>>> +	int flag;
>>>>>  	block_t lstart, start, len, total_len;
>>>>>  	int err = 0;
>>>>>  
>>>>> +	flag = dpolicy->sync ? REQ_SYNC : 0;
>>>>> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
>>>>> +
>>>>>  	if (dc->state != D_PREP)
>>>>>  		return 0;
>>>>>  
>>>>> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>  		bio->bi_end_io = f2fs_submit_discard_endio;
>>>>>  		bio->bi_opf |= flag;
>>>>>  		submit_bio(bio);
>>>>> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
>>>>
>>>> If we want to update dc->state, we need to cover it with dc->lock.
>>>
>>> Sure, will update it.
>>>
>>>>
>>>>> +			dc->state = D_PREP;
>>>>
>>>> BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
>>>> D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
>>>> pending list... which is inconsistent status.
>>>
>>> In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state
>>> will not be updated to D_DONE in f2fs_submit_discard_endio()?
>>
>> __submit_discard_cmd()
>>  lock()
>>  dc->state = D_SUBMIT;
>>  dc->bio_ref++;
>>  unlock()
>> ...
>>  submit_bio()
>> 				f2fs_submit_discard_endio()
>> 				 dc->error = -EAGAIN;
>> 				 lock()
>> 				 dc->bio_ref--;
>>
>>  dc->state = D_PREP;
>>
>> 				 dc->state = D_DONE;
>> 				 unlock()
>>
>> So finally, dc's state is D_DONE, and it's in wait list, then will be relocated
>> to pending list.
> 
> In case of queue full, f2fs_submit_discard_endio() will not be called

I guess the case is there are multiple bios related to one dc and partially callback
of bio is called asynchronously and the other is called synchronously, so the race
condition could happen.

Thanks,

> asynchronously. It will be called in the context of submit_bio() itself.
> So by the time, submit_bio returns dc->error will be -EAGAIN and dc->state
> will be D_DONE. 
> 
> submit_bio()
> ->blk_mq_make_request
> ->blk_mq_get_request()
>   ->bio_wouldblock_error() (called due to queue full)
>     ->bio_endio()
>     
> Thanks,
>>
>>>
>>> Thanks,
>>>
>>>>
>>>> Thanks,
>>>>
>>>>> +			err = dc->error;
>>>>> +			break;
>>>>> +		}
>>>>>  
>>>>>  		atomic_inc(&dcc->issued_discard);
>>>>>  
>>>>> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>  			}
>>>>>  
>>>>>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
>>>>> +			if (dc->error == -EAGAIN) {
>>>>> +				congestion_wait(BLK_RW_ASYNC, HZ/50);
>>>>> +				__relocate_discard_cmd(dcc, dc);
>>>>> +			}
>>>>>  
>>>>>  			if (issued >= dpolicy->max_requests)
>>>>>  				break;
>>>>>
>>>
> 


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Re: [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

Hi Chao,

On Mon, Mar 16, 2020 at 08:52:25AM +0800, Chao Yu wrote:
> On 2020/3/13 19:08, Sahitya Tummala wrote:
> > On Fri, Mar 13, 2020 at 02:30:55PM +0800, Chao Yu wrote:
> >> On 2020/3/13 11:39, Sahitya Tummala wrote:
> >>> On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote:
> >>>> On 2020/3/12 19:14, Sahitya Tummala wrote:
> >>>>> F2FS already has a default timeout of 5 secs for discards that
> >>>>> can be issued during umount, but it can take more than the 5 sec
> >>>>> timeout if the underlying UFS device queue is already full and there
> >>>>> are no more available free tags to be used. In that case, submit_bio()
> >>>>> will wait for the already queued discard requests to complete to get
> >>>>> a free tag, which can potentially take way more than 5 sec.
> >>>>>
> >>>>> Fix this by submitting the discard requests with REQ_NOWAIT
> >>>>> flags during umount. This will return -EAGAIN for UFS queue/tag full
> >>>>> scenario without waiting in the context of submit_bio(). The FS can
> >>>>> then handle these requests by retrying again within the stipulated
> >>>>> discard timeout period to avoid long latencies.
> >>>>>
> >>>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> >>>>> ---
> >>>>>  fs/f2fs/segment.c | 14 +++++++++++++-
> >>>>>  1 file changed, 13 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>>>> index fb3e531..a06bbac 100644
> >>>>> --- a/fs/f2fs/segment.c
> >>>>> +++ b/fs/f2fs/segment.c
> >>>>> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>>>>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> >>>>>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> >>>>> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> >>>>> +	int flag;
> >>>>>  	block_t lstart, start, len, total_len;
> >>>>>  	int err = 0;
> >>>>>  
> >>>>> +	flag = dpolicy->sync ? REQ_SYNC : 0;
> >>>>> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> >>>>> +
> >>>>>  	if (dc->state != D_PREP)
> >>>>>  		return 0;
> >>>>>  
> >>>>> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>>>  		bio->bi_end_io = f2fs_submit_discard_endio;
> >>>>>  		bio->bi_opf |= flag;
> >>>>>  		submit_bio(bio);
> >>>>> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> >>>>
> >>>> If we want to update dc->state, we need to cover it with dc->lock.
> >>>
> >>> Sure, will update it.
> >>>
> >>>>
> >>>>> +			dc->state = D_PREP;
> >>>>
> >>>> BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
> >>>> D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
> >>>> pending list... which is inconsistent status.
> >>>
> >>> In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state
> >>> will not be updated to D_DONE in f2fs_submit_discard_endio()?
> >>
> >> __submit_discard_cmd()
> >>  lock()
> >>  dc->state = D_SUBMIT;
> >>  dc->bio_ref++;
> >>  unlock()
> >> ...
> >>  submit_bio()
> >> 				f2fs_submit_discard_endio()
> >> 				 dc->error = -EAGAIN;
> >> 				 lock()
> >> 				 dc->bio_ref--;
> >>
> >>  dc->state = D_PREP;
> >>
> >> 				 dc->state = D_DONE;
> >> 				 unlock()
> >>
> >> So finally, dc's state is D_DONE, and it's in wait list, then will be relocated
> >> to pending list.
> > 
> > In case of queue full, f2fs_submit_discard_endio() will not be called
> 
> I guess the case is there are multiple bios related to one dc and partially callback
> of bio is called asynchronously and the other is called synchronously, so the race
> condition could happen.

You are right. Let me review that case and try to fix it.

Thanks,

> 
> Thanks,
> 
> > asynchronously. It will be called in the context of submit_bio() itself.
> > So by the time, submit_bio returns dc->error will be -EAGAIN and dc->state
> > will be D_DONE. 
> > 
> > submit_bio()
> > ->blk_mq_make_request
> > ->blk_mq_get_request()
> >   ->bio_wouldblock_error() (called due to queue full)
> >     ->bio_endio()
> >     
> > Thanks,
> >>
> >>>
> >>> Thanks,
> >>>
> >>>>
> >>>> Thanks,
> >>>>
> >>>>> +			err = dc->error;
> >>>>> +			break;
> >>>>> +		}
> >>>>>  
> >>>>>  		atomic_inc(&dcc->issued_discard);
> >>>>>  
> >>>>> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>>>  			}
> >>>>>  
> >>>>>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> >>>>> +			if (dc->error == -EAGAIN) {
> >>>>> +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> >>>>> +				__relocate_discard_cmd(dcc, dc);
> >>>>> +			}
> >>>>>  
> >>>>>  			if (issued >= dpolicy->max_requests)
> >>>>>  				break;
> >>>>>
> >>>
> > 

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

Hi Chao,

On Mon, Mar 16, 2020 at 08:52:25AM +0800, Chao Yu wrote:
> On 2020/3/13 19:08, Sahitya Tummala wrote:
> > On Fri, Mar 13, 2020 at 02:30:55PM +0800, Chao Yu wrote:
> >> On 2020/3/13 11:39, Sahitya Tummala wrote:
> >>> On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote:
> >>>> On 2020/3/12 19:14, Sahitya Tummala wrote:
> >>>>> F2FS already has a default timeout of 5 secs for discards that
> >>>>> can be issued during umount, but it can take more than the 5 sec
> >>>>> timeout if the underlying UFS device queue is already full and there
> >>>>> are no more available free tags to be used. In that case, submit_bio()
> >>>>> will wait for the already queued discard requests to complete to get
> >>>>> a free tag, which can potentially take way more than 5 sec.
> >>>>>
> >>>>> Fix this by submitting the discard requests with REQ_NOWAIT
> >>>>> flags during umount. This will return -EAGAIN for UFS queue/tag full
> >>>>> scenario without waiting in the context of submit_bio(). The FS can
> >>>>> then handle these requests by retrying again within the stipulated
> >>>>> discard timeout period to avoid long latencies.
> >>>>>
> >>>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> >>>>> ---
> >>>>>  fs/f2fs/segment.c | 14 +++++++++++++-
> >>>>>  1 file changed, 13 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>>>> index fb3e531..a06bbac 100644
> >>>>> --- a/fs/f2fs/segment.c
> >>>>> +++ b/fs/f2fs/segment.c
> >>>>> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>>>>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> >>>>>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> >>>>> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> >>>>> +	int flag;
> >>>>>  	block_t lstart, start, len, total_len;
> >>>>>  	int err = 0;
> >>>>>  
> >>>>> +	flag = dpolicy->sync ? REQ_SYNC : 0;
> >>>>> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> >>>>> +
> >>>>>  	if (dc->state != D_PREP)
> >>>>>  		return 0;
> >>>>>  
> >>>>> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>>>  		bio->bi_end_io = f2fs_submit_discard_endio;
> >>>>>  		bio->bi_opf |= flag;
> >>>>>  		submit_bio(bio);
> >>>>> +		if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) {
> >>>>
> >>>> If we want to update dc->state, we need to cover it with dc->lock.
> >>>
> >>> Sure, will update it.
> >>>
> >>>>
> >>>>> +			dc->state = D_PREP;
> >>>>
> >>>> BTW, one dc can be referenced by multiple bios, so dc->state could be updated to
> >>>> D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to
> >>>> pending list... which is inconsistent status.
> >>>
> >>> In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state
> >>> will not be updated to D_DONE in f2fs_submit_discard_endio()?
> >>
> >> __submit_discard_cmd()
> >>  lock()
> >>  dc->state = D_SUBMIT;
> >>  dc->bio_ref++;
> >>  unlock()
> >> ...
> >>  submit_bio()
> >> 				f2fs_submit_discard_endio()
> >> 				 dc->error = -EAGAIN;
> >> 				 lock()
> >> 				 dc->bio_ref--;
> >>
> >>  dc->state = D_PREP;
> >>
> >> 				 dc->state = D_DONE;
> >> 				 unlock()
> >>
> >> So finally, dc's state is D_DONE, and it's in wait list, then will be relocated
> >> to pending list.
> > 
> > In case of queue full, f2fs_submit_discard_endio() will not be called
> 
> I guess the case is there are multiple bios related to one dc and partially callback
> of bio is called asynchronously and the other is called synchronously, so the race
> condition could happen.

You are right. Let me review that case and try to fix it.

Thanks,

> 
> Thanks,
> 
> > asynchronously. It will be called in the context of submit_bio() itself.
> > So by the time, submit_bio returns dc->error will be -EAGAIN and dc->state
> > will be D_DONE. 
> > 
> > submit_bio()
> > ->blk_mq_make_request
> > ->blk_mq_get_request()
> >   ->bio_wouldblock_error() (called due to queue full)
> >     ->bio_endio()
> >     
> > Thanks,
> >>
> >>>
> >>> Thanks,
> >>>
> >>>>
> >>>> Thanks,
> >>>>
> >>>>> +			err = dc->error;
> >>>>> +			break;
> >>>>> +		}
> >>>>>  
> >>>>>  		atomic_inc(&dcc->issued_discard);
> >>>>>  
> >>>>> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>>>  			}
> >>>>>  
> >>>>>  			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> >>>>> +			if (dc->error == -EAGAIN) {
> >>>>> +				congestion_wait(BLK_RW_ASYNC, HZ/50);
> >>>>> +				__relocate_discard_cmd(dcc, dc);
> >>>>> +			}
> >>>>>  
> >>>>>  			if (issued >= dpolicy->max_requests)
> >>>>>  				break;
> >>>>>
> >>>
> > 

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


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Re: [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

Hi Sahitya,

Bad news, :( I guess we didn't catch the root cause, as after applying v3,
I still can reproduce this issue:

generic/003 10s ...  30s

Thanks,

On 2020/3/30 14:53, Sahitya Tummala wrote:
> Hi Chao,
> 
> On Fri, Mar 27, 2020 at 08:35:42AM +0530, Sahitya Tummala wrote:
>> On Fri, Mar 27, 2020 at 09:51:43AM +0800, Chao Yu wrote:
>>>
>>> With this patch, most of xfstest cases cost 5 * n second longer than before.
>>>
>>> E.g. generic/003, during umount(), we looped into retrying one bio
>>> submission.
>>>
>>> [61279.829724] F2FS-fs (zram1): Found nat_bits in checkpoint
>>> [61279.885337] F2FS-fs (zram1): Mounted with checkpoint version = 5cf3cb8e
>>> [61281.912832] submit discard bio start [23555,1]
>>> [61281.912835] f2fs_submit_discard_endio [23555,1] err:-11
>>> [61281.912836] submit discard bio end [23555,1]
>>> [61281.912836] move dc to retry list [23555,1]
>>>
>>> ...
>>>
>>> [61286.881212] submit discard bio start [23555,1]
>>> [61286.881217] f2fs_submit_discard_endio [23555,1] err:-11
>>> [61286.881223] submit discard bio end [23555,1]
>>> [61286.881224] move dc to retry list [23555,1]
>>> [61286.905198] submit discard bio start [23555,1]
>>> [61286.905203] f2fs_submit_discard_endio [23555,1] err:-11
>>> [61286.905205] submit discard bio end [23555,1]
>>> [61286.905206] move dc to retry list [23555,1]
>>> [61286.929157] F2FS-fs (zram1): Issue discard(23555, 23555, 1) failed, ret: -11
>>>
>>> Could you take a look at this issue?
>>
>> Let me check and get back on this.
> 
> I found the issue. The dc with multiple bios is getting requeued again and
> again in case if one of its bio gets -EAGAIN error. Even the successfully
> completed bios are getting requeued again resulting into long latency.
> I have fixed it by splitting the dc in such case so that we can requeue only
> the leftover bios into a new dc and retry that later within the 5 sec timeout.
> 
> Please help to review v3 posted and if it looks good, I would like to request
> you to test the earlier regression scenario with it to check the result again?
> 
> thanks,
> 
>>
>> Thanks,
>>
>>>
>>> Thanks,
>>>
>>>>
>>>> Thanks,
>>>>
>>>>> Thanks,
>>>>>
>>>>>> +				break;
>>>>>> +			}
>>>>>> +		}
>>>>>>  
>>>>>>  		atomic_inc(&dcc->issued_discard);
>>>>>>  
>>>>>> @@ -1463,6 +1477,40 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
>>>>>>  	return issued;
>>>>>>  }
>>>>>>  
>>>>>> +static bool __should_discard_retry(struct f2fs_sb_info *sbi,
>>>> s> > +		struct discard_policy *dpolicy)
>>>>>> +{
>>>>>> +	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>>>>>> +	struct discard_cmd *dc, *tmp;
>>>>>> +	bool retry = false;
>>>>>> +	unsigned long flags;
>>>>>> +
>>>>>> +	if (dpolicy->type != DPOLICY_UMOUNT)
>>>>>> +		f2fs_bug_on(sbi, 1);
>>>>>> +
>>>>>> +	mutex_lock(&dcc->cmd_lock);
>>>>>> +	list_for_each_entry_safe(dc, tmp, &(dcc->retry_list), list) {
>>>>>> +		if (dpolicy->timeout != 0 &&
>>>>>> +			f2fs_time_over(sbi, dpolicy->timeout)) {
>>>>>> +			retry = false;
>>>>>> +			break;
>>>>>> +		}
>>>>>> +
>>>>>> +		spin_lock_irqsave(&dc->lock, flags);
>>>>>> +		if (!dc->bio_ref) {
>>>>>> +			dc->state = D_PREP;
>>>>>> +			dc->error = 0;
>>>>>> +			reinit_completion(&dc->wait);
>>>>>> +			__relocate_discard_cmd(dcc, dc);
>>>>>> +			retry = true;
>>>>>> +		}
>>>>>> +		spin_unlock_irqrestore(&dc->lock, flags);
>>>>>> +	}
>>>>>> +	mutex_unlock(&dcc->cmd_lock);
>>>>>> +
>>>>>> +	return retry;
>>>>>> +}
>>>>>> +
>>>>>>  static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>>  					struct discard_policy *dpolicy)
>>>>>>  {
>>>>>> @@ -1470,12 +1518,13 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>>  	struct list_head *pend_list;
>>>>>>  	struct discard_cmd *dc, *tmp;
>>>>>>  	struct blk_plug plug;
>>>>>> -	int i, issued = 0;
>>>>>> +	int i, err, issued = 0;
>>>>>>  	bool io_interrupted = false;
>>>>>>  
>>>>>>  	if (dpolicy->timeout != 0)
>>>>>>  		f2fs_update_time(sbi, dpolicy->timeout);
>>>>>>  
>>>>>> +retry:
>>>>>>  	for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
>>>>>>  		if (dpolicy->timeout != 0 &&
>>>>>>  				f2fs_time_over(sbi, dpolicy->timeout))
>>>>>> @@ -1509,7 +1558,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>>  				break;
>>>>>>  			}
>>>>>>  
>>>>>> -			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
>>>>>> +			err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
>>>>>> +			if (err == -EAGAIN)
>>>>>> +				congestion_wait(BLK_RW_ASYNC,
>>>>>> +						DEFAULT_IO_TIMEOUT);
>>>>>>  
>>>>>>  			if (issued >= dpolicy->max_requests)
>>>>>>  				break;
>>>>>> @@ -1522,6 +1574,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>>>>  			break;
>>>>>>  	}
>>>>>>  
>>>>>> +	if (!list_empty(&dcc->retry_list) &&
>>>>>> +		__should_discard_retry(sbi, dpolicy))
>>>>>> +		goto retry;
>>>>>> +
>>>>>>  	if (!issued && io_interrupted)
>>>>>>  		issued = -1;
>>>>>>  
>>>>>> @@ -1613,6 +1669,12 @@ static unsigned int __wait_discard_cmd_range(struct f2fs_sb_info *sbi,
>>>>>>  		goto next;
>>>>>>  	}
>>>>>>  
>>>>>> +	if (dpolicy->type == DPOLICY_UMOUNT &&
>>>>>> +		!list_empty(&dcc->retry_list)) {
>>>>>> +		wait_list = &dcc->retry_list;
>>>>>> +		goto next;
>>>>>> +	}
>>>>>> +
>>>>>>  	return trimmed;
>>>>>>  }
>>>>>>  
>>>>>> @@ -2051,6 +2113,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
>>>>>>  	for (i = 0; i < MAX_PLIST_NUM; i++)
>>>>>>  		INIT_LIST_HEAD(&dcc->pend_list[i]);
>>>>>>  	INIT_LIST_HEAD(&dcc->wait_list);
>>>>>> +	INIT_LIST_HEAD(&dcc->retry_list);
>>>>>>  	INIT_LIST_HEAD(&dcc->fstrim_list);
>>>>>>  	mutex_init(&dcc->cmd_lock);
>>>>>>  	atomic_set(&dcc->issued_discard, 0);
>>>>>>
>>>>
>>
>> -- 
>> --
>> Sent by a consultant of the Qualcomm Innovation Center, Inc.
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
> 

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

Hi Chao,

On Fri, Mar 27, 2020 at 08:35:42AM +0530, Sahitya Tummala wrote:
> On Fri, Mar 27, 2020 at 09:51:43AM +0800, Chao Yu wrote:
> > 
> > With this patch, most of xfstest cases cost 5 * n second longer than before.
> > 
> > E.g. generic/003, during umount(), we looped into retrying one bio
> > submission.
> > 
> > [61279.829724] F2FS-fs (zram1): Found nat_bits in checkpoint
> > [61279.885337] F2FS-fs (zram1): Mounted with checkpoint version = 5cf3cb8e
> > [61281.912832] submit discard bio start [23555,1]
> > [61281.912835] f2fs_submit_discard_endio [23555,1] err:-11
> > [61281.912836] submit discard bio end [23555,1]
> > [61281.912836] move dc to retry list [23555,1]
> > 
> > ...
> > 
> > [61286.881212] submit discard bio start [23555,1]
> > [61286.881217] f2fs_submit_discard_endio [23555,1] err:-11
> > [61286.881223] submit discard bio end [23555,1]
> > [61286.881224] move dc to retry list [23555,1]
> > [61286.905198] submit discard bio start [23555,1]
> > [61286.905203] f2fs_submit_discard_endio [23555,1] err:-11
> > [61286.905205] submit discard bio end [23555,1]
> > [61286.905206] move dc to retry list [23555,1]
> > [61286.929157] F2FS-fs (zram1): Issue discard(23555, 23555, 1) failed, ret: -11
> > 
> > Could you take a look at this issue?
> 
> Let me check and get back on this.

I found the issue. The dc with multiple bios is getting requeued again and
again in case if one of its bio gets -EAGAIN error. Even the successfully
completed bios are getting requeued again resulting into long latency.
I have fixed it by splitting the dc in such case so that we can requeue only
the leftover bios into a new dc and retry that later within the 5 sec timeout.

Please help to review v3 posted and if it looks good, I would like to request
you to test the earlier regression scenario with it to check the result again?

thanks,

> 
> Thanks,
> 
> > 
> > Thanks,
> > 
> > > 
> > > Thanks,
> > > 
> > >> Thanks,
> > >>
> > >>> +				break;
> > >>> +			}
> > >>> +		}
> > >>>  
> > >>>  		atomic_inc(&dcc->issued_discard);
> > >>>  
> > >>> @@ -1463,6 +1477,40 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
> > >>>  	return issued;
> > >>>  }
> > >>>  
> > >>> +static bool __should_discard_retry(struct f2fs_sb_info *sbi,
> > > s> > +		struct discard_policy *dpolicy)
> > >>> +{
> > >>> +	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > >>> +	struct discard_cmd *dc, *tmp;
> > >>> +	bool retry = false;
> > >>> +	unsigned long flags;
> > >>> +
> > >>> +	if (dpolicy->type != DPOLICY_UMOUNT)
> > >>> +		f2fs_bug_on(sbi, 1);
> > >>> +
> > >>> +	mutex_lock(&dcc->cmd_lock);
> > >>> +	list_for_each_entry_safe(dc, tmp, &(dcc->retry_list), list) {
> > >>> +		if (dpolicy->timeout != 0 &&
> > >>> +			f2fs_time_over(sbi, dpolicy->timeout)) {
> > >>> +			retry = false;
> > >>> +			break;
> > >>> +		}
> > >>> +
> > >>> +		spin_lock_irqsave(&dc->lock, flags);
> > >>> +		if (!dc->bio_ref) {
> > >>> +			dc->state = D_PREP;
> > >>> +			dc->error = 0;
> > >>> +			reinit_completion(&dc->wait);
> > >>> +			__relocate_discard_cmd(dcc, dc);
> > >>> +			retry = true;
> > >>> +		}
> > >>> +		spin_unlock_irqrestore(&dc->lock, flags);
> > >>> +	}
> > >>> +	mutex_unlock(&dcc->cmd_lock);
> > >>> +
> > >>> +	return retry;
> > >>> +}
> > >>> +
> > >>>  static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > >>>  					struct discard_policy *dpolicy)
> > >>>  {
> > >>> @@ -1470,12 +1518,13 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > >>>  	struct list_head *pend_list;
> > >>>  	struct discard_cmd *dc, *tmp;
> > >>>  	struct blk_plug plug;
> > >>> -	int i, issued = 0;
> > >>> +	int i, err, issued = 0;
> > >>>  	bool io_interrupted = false;
> > >>>  
> > >>>  	if (dpolicy->timeout != 0)
> > >>>  		f2fs_update_time(sbi, dpolicy->timeout);
> > >>>  
> > >>> +retry:
> > >>>  	for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
> > >>>  		if (dpolicy->timeout != 0 &&
> > >>>  				f2fs_time_over(sbi, dpolicy->timeout))
> > >>> @@ -1509,7 +1558,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > >>>  				break;
> > >>>  			}
> > >>>  
> > >>> -			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > >>> +			err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > >>> +			if (err == -EAGAIN)
> > >>> +				congestion_wait(BLK_RW_ASYNC,
> > >>> +						DEFAULT_IO_TIMEOUT);
> > >>>  
> > >>>  			if (issued >= dpolicy->max_requests)
> > >>>  				break;
> > >>> @@ -1522,6 +1574,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > >>>  			break;
> > >>>  	}
> > >>>  
> > >>> +	if (!list_empty(&dcc->retry_list) &&
> > >>> +		__should_discard_retry(sbi, dpolicy))
> > >>> +		goto retry;
> > >>> +
> > >>>  	if (!issued && io_interrupted)
> > >>>  		issued = -1;
> > >>>  
> > >>> @@ -1613,6 +1669,12 @@ static unsigned int __wait_discard_cmd_range(struct f2fs_sb_info *sbi,
> > >>>  		goto next;
> > >>>  	}
> > >>>  
> > >>> +	if (dpolicy->type == DPOLICY_UMOUNT &&
> > >>> +		!list_empty(&dcc->retry_list)) {
> > >>> +		wait_list = &dcc->retry_list;
> > >>> +		goto next;
> > >>> +	}
> > >>> +
> > >>>  	return trimmed;
> > >>>  }
> > >>>  
> > >>> @@ -2051,6 +2113,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
> > >>>  	for (i = 0; i < MAX_PLIST_NUM; i++)
> > >>>  		INIT_LIST_HEAD(&dcc->pend_list[i]);
> > >>>  	INIT_LIST_HEAD(&dcc->wait_list);
> > >>> +	INIT_LIST_HEAD(&dcc->retry_list);
> > >>>  	INIT_LIST_HEAD(&dcc->fstrim_list);
> > >>>  	mutex_init(&dcc->cmd_lock);
> > >>>  	atomic_set(&dcc->issued_discard, 0);
> > >>>
> > > 
> 
> -- 
> --
> Sent by a consultant of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

On Fri, Mar 27, 2020 at 09:51:43AM +0800, Chao Yu wrote:
> On 2020/3/26 21:37, Sahitya Tummala wrote:
> > Hi Chao,
> > 
> > On Thu, Mar 26, 2020 at 05:00:18PM +0800, Chao Yu wrote:
> >> Hi Sahitya,
> >>
> >> On 2020/3/18 12:44, Sahitya Tummala wrote:
> >>> F2FS already has a default timeout of 5 secs for discards that
> >>> can be issued during umount, but it can take more than the 5 sec
> >>> timeout if the underlying UFS device queue is already full and there
> >>> are no more available free tags to be used. In that case, submit_bio()
> >>> will wait for the already queued discard requests to complete to get
> >>> a free tag, which can potentially take way more than 5 sec.
> >>>
> >>> Fix this by submitting the discard requests with REQ_NOWAIT
> >>> flags during umount. This will return -EAGAIN for UFS queue/tag full
> >>> scenario without waiting in the context of submit_bio(). The FS can
> >>> then handle these requests by retrying again within the stipulated
> >>> discard timeout period to avoid long latencies.
> >>>
> >>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> >>> ---
> >>> v2:
> >>> - Handle the case where a dc can have multiple bios associated with it
> >>>
> >>>  fs/f2fs/f2fs.h    |  1 +
> >>>  fs/f2fs/segment.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++-------
> >>>  2 files changed, 74 insertions(+), 10 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>> index 12a197e..67b8dcc 100644
> >>> --- a/fs/f2fs/f2fs.h
> >>> +++ b/fs/f2fs/f2fs.h
> >>> @@ -340,6 +340,7 @@ struct discard_cmd_control {
> >>>  	struct list_head pend_list[MAX_PLIST_NUM];/* store pending entries */
> >>>  	struct list_head wait_list;		/* store on-flushing entries */
> >>>  	struct list_head fstrim_list;		/* in-flight discard from fstrim */
> >>> +	struct list_head retry_list;		/* list of cmds to retry */
> >>>  	wait_queue_head_t discard_wait_queue;	/* waiting queue for wake-up */
> >>>  	unsigned int discard_wake;		/* to wake up discard thread */
> >>>  	struct mutex cmd_lock;
> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>> index fb3e531..4162c76 100644
> >>> --- a/fs/f2fs/segment.c
> >>> +++ b/fs/f2fs/segment.c
> >>> @@ -1029,13 +1029,16 @@ static void f2fs_submit_discard_endio(struct bio *bio)
> >>>  	struct discard_cmd *dc = (struct discard_cmd *)bio->bi_private;
> >>>  	unsigned long flags;
> >>>  
> >>> -	dc->error = blk_status_to_errno(bio->bi_status);
> >>> -
> >>>  	spin_lock_irqsave(&dc->lock, flags);
> >>> +	if (!dc->error)
> >>> +		dc->error = blk_status_to_errno(bio->bi_status);
> >>> +
> >>>  	dc->bio_ref--;
> >>> -	if (!dc->bio_ref && dc->state == D_SUBMIT) {
> >>> -		dc->state = D_DONE;
> >>> -		complete_all(&dc->wait);
> >>> +	if (!dc->bio_ref) {
> >>> +		if (dc->error || dc->state == D_SUBMIT) {
> >>> +			dc->state = D_DONE;
> >>> +			complete_all(&dc->wait);
> >>> +		}
> >>>  	}
> >>>  	spin_unlock_irqrestore(&dc->lock, flags);
> >>>  	bio_put(bio);
> >>> @@ -1124,10 +1127,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> >>>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> >>> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> >>> -	block_t lstart, start, len, total_len;
> >>> +	int flag;
> >>> +	block_t lstart, start, len, total_len, orig_len;
> >>>  	int err = 0;
> >>>  
> >>> +	flag = dpolicy->sync ? REQ_SYNC : 0;
> >>> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> >>> +
> >>>  	if (dc->state != D_PREP)
> >>>  		return 0;
> >>>  
> >>> @@ -1139,7 +1145,7 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  	lstart = dc->lstart;
> >>>  	start = dc->start;
> >>>  	len = dc->len;
> >>> -	total_len = len;
> >>> +	orig_len = total_len = len;
> >>>  
> >>>  	dc->len = 0;
> >>>  
> >>> @@ -1203,6 +1209,14 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  		bio->bi_end_io = f2fs_submit_discard_endio;
> >>>  		bio->bi_opf |= flag;
> >>>  		submit_bio(bio);
> >>> +		if (flag & REQ_NOWAIT) {
> >>> +			if (dc->error == -EAGAIN) {
> >>> +				dc->len = orig_len;
> >>> +				list_move(&dc->list, &dcc->retry_list);
> >>> +				err = dc->error;
> >>
> >> I encounter lots of dmesg, which should be printed by __remove_discard_cmd()
> >>
> >> F2FS-fs (dm-0): Issue discard(23552, 23552, 2) failed, ret: -11
> >>
> >> This should happen only if we didn't handle all discard in 5 seconds during
> >> umount.
> >>
> >> So I doubt we failed to move dc to retry_list, because after submit_bio(),
> >> end_io() is not called synchronously as the bio was just pluged?
> >>
> > This can happen if a discard cmd has multiple bios and at least 1 bio is 
> > already submitted and when submitting other bios, we encounter -EAGAIN.
> > In this case, this dc will be moved to retry_list and will be moved back
> > to dcc->pend_list only if the dc->bio_ref becomes 0 within 5 sec timeout.
> > If it doesn't become zero, then it will be left in retry_list itself, which
> > will be later removed from retry_list. Before removing from retry_list we 
> > will however ensure that submitted bio is done i.e., dc->bio_ref is 0, but
> > dc->error will be -EAGAIN as this dc could not be requeued/retried.
> > 
> > So this is expected, where it only means that this dc could not be
> > submitted/retried again within timeout. I think we can ignore
> > this -EAGAIN error in __remove_discard_cmd().
> 
> With this patch, most of xfstest cases cost 5 * n second longer than before.
> 
> E.g. generic/003, during umount(), we looped into retrying one bio
> submission.
> 
> [61279.829724] F2FS-fs (zram1): Found nat_bits in checkpoint
> [61279.885337] F2FS-fs (zram1): Mounted with checkpoint version = 5cf3cb8e
> [61281.912832] submit discard bio start [23555,1]
> [61281.912835] f2fs_submit_discard_endio [23555,1] err:-11
> [61281.912836] submit discard bio end [23555,1]
> [61281.912836] move dc to retry list [23555,1]
> 
> ...
> 
> [61286.881212] submit discard bio start [23555,1]
> [61286.881217] f2fs_submit_discard_endio [23555,1] err:-11
> [61286.881223] submit discard bio end [23555,1]
> [61286.881224] move dc to retry list [23555,1]
> [61286.905198] submit discard bio start [23555,1]
> [61286.905203] f2fs_submit_discard_endio [23555,1] err:-11
> [61286.905205] submit discard bio end [23555,1]
> [61286.905206] move dc to retry list [23555,1]
> [61286.929157] F2FS-fs (zram1): Issue discard(23555, 23555, 1) failed, ret: -11
> 
> Could you take a look at this issue?

Let me check and get back on this.

Thanks,

> 
> Thanks,
> 
> > 
> > Thanks,
> > 
> >> Thanks,
> >>
> >>> +				break;
> >>> +			}
> >>> +		}
> >>>  
> >>>  		atomic_inc(&dcc->issued_discard);
> >>>  
> >>> @@ -1463,6 +1477,40 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
> >>>  	return issued;
> >>>  }
> >>>  
> >>> +static bool __should_discard_retry(struct f2fs_sb_info *sbi,
> > s> > +		struct discard_policy *dpolicy)
> >>> +{
> >>> +	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>> +	struct discard_cmd *dc, *tmp;
> >>> +	bool retry = false;
> >>> +	unsigned long flags;
> >>> +
> >>> +	if (dpolicy->type != DPOLICY_UMOUNT)
> >>> +		f2fs_bug_on(sbi, 1);
> >>> +
> >>> +	mutex_lock(&dcc->cmd_lock);
> >>> +	list_for_each_entry_safe(dc, tmp, &(dcc->retry_list), list) {
> >>> +		if (dpolicy->timeout != 0 &&
> >>> +			f2fs_time_over(sbi, dpolicy->timeout)) {
> >>> +			retry = false;
> >>> +			break;
> >>> +		}
> >>> +
> >>> +		spin_lock_irqsave(&dc->lock, flags);
> >>> +		if (!dc->bio_ref) {
> >>> +			dc->state = D_PREP;
> >>> +			dc->error = 0;
> >>> +			reinit_completion(&dc->wait);
> >>> +			__relocate_discard_cmd(dcc, dc);
> >>> +			retry = true;
> >>> +		}
> >>> +		spin_unlock_irqrestore(&dc->lock, flags);
> >>> +	}
> >>> +	mutex_unlock(&dcc->cmd_lock);
> >>> +
> >>> +	return retry;
> >>> +}
> >>> +
> >>>  static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  					struct discard_policy *dpolicy)
> >>>  {
> >>> @@ -1470,12 +1518,13 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  	struct list_head *pend_list;
> >>>  	struct discard_cmd *dc, *tmp;
> >>>  	struct blk_plug plug;
> >>> -	int i, issued = 0;
> >>> +	int i, err, issued = 0;
> >>>  	bool io_interrupted = false;
> >>>  
> >>>  	if (dpolicy->timeout != 0)
> >>>  		f2fs_update_time(sbi, dpolicy->timeout);
> >>>  
> >>> +retry:
> >>>  	for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
> >>>  		if (dpolicy->timeout != 0 &&
> >>>  				f2fs_time_over(sbi, dpolicy->timeout))
> >>> @@ -1509,7 +1558,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  				break;
> >>>  			}
> >>>  
> >>> -			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> >>> +			err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> >>> +			if (err == -EAGAIN)
> >>> +				congestion_wait(BLK_RW_ASYNC,
> >>> +						DEFAULT_IO_TIMEOUT);
> >>>  
> >>>  			if (issued >= dpolicy->max_requests)
> >>>  				break;
> >>> @@ -1522,6 +1574,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>  			break;
> >>>  	}
> >>>  
> >>> +	if (!list_empty(&dcc->retry_list) &&
> >>> +		__should_discard_retry(sbi, dpolicy))
> >>> +		goto retry;
> >>> +
> >>>  	if (!issued && io_interrupted)
> >>>  		issued = -1;
> >>>  
> >>> @@ -1613,6 +1669,12 @@ static unsigned int __wait_discard_cmd_range(struct f2fs_sb_info *sbi,
> >>>  		goto next;
> >>>  	}
> >>>  
> >>> +	if (dpolicy->type == DPOLICY_UMOUNT &&
> >>> +		!list_empty(&dcc->retry_list)) {
> >>> +		wait_list = &dcc->retry_list;
> >>> +		goto next;
> >>> +	}
> >>> +
> >>>  	return trimmed;
> >>>  }
> >>>  
> >>> @@ -2051,6 +2113,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
> >>>  	for (i = 0; i < MAX_PLIST_NUM; i++)
> >>>  		INIT_LIST_HEAD(&dcc->pend_list[i]);
> >>>  	INIT_LIST_HEAD(&dcc->wait_list);
> >>> +	INIT_LIST_HEAD(&dcc->retry_list);
> >>>  	INIT_LIST_HEAD(&dcc->fstrim_list);
> >>>  	mutex_init(&dcc->cmd_lock);
> >>>  	atomic_set(&dcc->issued_discard, 0);
> >>>
> > 

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

On 2020/3/26 21:37, Sahitya Tummala wrote:
> Hi Chao,
> 
> On Thu, Mar 26, 2020 at 05:00:18PM +0800, Chao Yu wrote:
>> Hi Sahitya,
>>
>> On 2020/3/18 12:44, Sahitya Tummala wrote:
>>> F2FS already has a default timeout of 5 secs for discards that
>>> can be issued during umount, but it can take more than the 5 sec
>>> timeout if the underlying UFS device queue is already full and there
>>> are no more available free tags to be used. In that case, submit_bio()
>>> will wait for the already queued discard requests to complete to get
>>> a free tag, which can potentially take way more than 5 sec.
>>>
>>> Fix this by submitting the discard requests with REQ_NOWAIT
>>> flags during umount. This will return -EAGAIN for UFS queue/tag full
>>> scenario without waiting in the context of submit_bio(). The FS can
>>> then handle these requests by retrying again within the stipulated
>>> discard timeout period to avoid long latencies.
>>>
>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
>>> ---
>>> v2:
>>> - Handle the case where a dc can have multiple bios associated with it
>>>
>>>  fs/f2fs/f2fs.h    |  1 +
>>>  fs/f2fs/segment.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++-------
>>>  2 files changed, 74 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 12a197e..67b8dcc 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -340,6 +340,7 @@ struct discard_cmd_control {
>>>  	struct list_head pend_list[MAX_PLIST_NUM];/* store pending entries */
>>>  	struct list_head wait_list;		/* store on-flushing entries */
>>>  	struct list_head fstrim_list;		/* in-flight discard from fstrim */
>>> +	struct list_head retry_list;		/* list of cmds to retry */
>>>  	wait_queue_head_t discard_wait_queue;	/* waiting queue for wake-up */
>>>  	unsigned int discard_wake;		/* to wake up discard thread */
>>>  	struct mutex cmd_lock;
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index fb3e531..4162c76 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -1029,13 +1029,16 @@ static void f2fs_submit_discard_endio(struct bio *bio)
>>>  	struct discard_cmd *dc = (struct discard_cmd *)bio->bi_private;
>>>  	unsigned long flags;
>>>  
>>> -	dc->error = blk_status_to_errno(bio->bi_status);
>>> -
>>>  	spin_lock_irqsave(&dc->lock, flags);
>>> +	if (!dc->error)
>>> +		dc->error = blk_status_to_errno(bio->bi_status);
>>> +
>>>  	dc->bio_ref--;
>>> -	if (!dc->bio_ref && dc->state == D_SUBMIT) {
>>> -		dc->state = D_DONE;
>>> -		complete_all(&dc->wait);
>>> +	if (!dc->bio_ref) {
>>> +		if (dc->error || dc->state == D_SUBMIT) {
>>> +			dc->state = D_DONE;
>>> +			complete_all(&dc->wait);
>>> +		}
>>>  	}
>>>  	spin_unlock_irqrestore(&dc->lock, flags);
>>>  	bio_put(bio);
>>> @@ -1124,10 +1127,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>>>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>>>  					&(dcc->fstrim_list) : &(dcc->wait_list);
>>> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
>>> -	block_t lstart, start, len, total_len;
>>> +	int flag;
>>> +	block_t lstart, start, len, total_len, orig_len;
>>>  	int err = 0;
>>>  
>>> +	flag = dpolicy->sync ? REQ_SYNC : 0;
>>> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
>>> +
>>>  	if (dc->state != D_PREP)
>>>  		return 0;
>>>  
>>> @@ -1139,7 +1145,7 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>  	lstart = dc->lstart;
>>>  	start = dc->start;
>>>  	len = dc->len;
>>> -	total_len = len;
>>> +	orig_len = total_len = len;
>>>  
>>>  	dc->len = 0;
>>>  
>>> @@ -1203,6 +1209,14 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>  		bio->bi_end_io = f2fs_submit_discard_endio;
>>>  		bio->bi_opf |= flag;
>>>  		submit_bio(bio);
>>> +		if (flag & REQ_NOWAIT) {
>>> +			if (dc->error == -EAGAIN) {
>>> +				dc->len = orig_len;
>>> +				list_move(&dc->list, &dcc->retry_list);
>>> +				err = dc->error;
>>
>> I encounter lots of dmesg, which should be printed by __remove_discard_cmd()
>>
>> F2FS-fs (dm-0): Issue discard(23552, 23552, 2) failed, ret: -11
>>
>> This should happen only if we didn't handle all discard in 5 seconds during
>> umount.
>>
>> So I doubt we failed to move dc to retry_list, because after submit_bio(),
>> end_io() is not called synchronously as the bio was just pluged?
>>
> This can happen if a discard cmd has multiple bios and at least 1 bio is 
> already submitted and when submitting other bios, we encounter -EAGAIN.
> In this case, this dc will be moved to retry_list and will be moved back
> to dcc->pend_list only if the dc->bio_ref becomes 0 within 5 sec timeout.
> If it doesn't become zero, then it will be left in retry_list itself, which
> will be later removed from retry_list. Before removing from retry_list we 
> will however ensure that submitted bio is done i.e., dc->bio_ref is 0, but
> dc->error will be -EAGAIN as this dc could not be requeued/retried.
> 
> So this is expected, where it only means that this dc could not be
> submitted/retried again within timeout. I think we can ignore
> this -EAGAIN error in __remove_discard_cmd().

With this patch, most of xfstest cases cost 5 * n second longer than before.

E.g. generic/003, during umount(), we looped into retrying one bio
submission.

[61279.829724] F2FS-fs (zram1): Found nat_bits in checkpoint
[61279.885337] F2FS-fs (zram1): Mounted with checkpoint version = 5cf3cb8e
[61281.912832] submit discard bio start [23555,1]
[61281.912835] f2fs_submit_discard_endio [23555,1] err:-11
[61281.912836] submit discard bio end [23555,1]
[61281.912836] move dc to retry list [23555,1]

...

[61286.881212] submit discard bio start [23555,1]
[61286.881217] f2fs_submit_discard_endio [23555,1] err:-11
[61286.881223] submit discard bio end [23555,1]
[61286.881224] move dc to retry list [23555,1]
[61286.905198] submit discard bio start [23555,1]
[61286.905203] f2fs_submit_discard_endio [23555,1] err:-11
[61286.905205] submit discard bio end [23555,1]
[61286.905206] move dc to retry list [23555,1]
[61286.929157] F2FS-fs (zram1): Issue discard(23555, 23555, 1) failed, ret: -11

Could you take a look at this issue?

Thanks,

> 
> Thanks,
> 
>> Thanks,
>>
>>> +				break;
>>> +			}
>>> +		}
>>>  
>>>  		atomic_inc(&dcc->issued_discard);
>>>  
>>> @@ -1463,6 +1477,40 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
>>>  	return issued;
>>>  }
>>>  
>>> +static bool __should_discard_retry(struct f2fs_sb_info *sbi,
> s> > +		struct discard_policy *dpolicy)
>>> +{
>>> +	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>>> +	struct discard_cmd *dc, *tmp;
>>> +	bool retry = false;
>>> +	unsigned long flags;
>>> +
>>> +	if (dpolicy->type != DPOLICY_UMOUNT)
>>> +		f2fs_bug_on(sbi, 1);
>>> +
>>> +	mutex_lock(&dcc->cmd_lock);
>>> +	list_for_each_entry_safe(dc, tmp, &(dcc->retry_list), list) {
>>> +		if (dpolicy->timeout != 0 &&
>>> +			f2fs_time_over(sbi, dpolicy->timeout)) {
>>> +			retry = false;
>>> +			break;
>>> +		}
>>> +
>>> +		spin_lock_irqsave(&dc->lock, flags);
>>> +		if (!dc->bio_ref) {
>>> +			dc->state = D_PREP;
>>> +			dc->error = 0;
>>> +			reinit_completion(&dc->wait);
>>> +			__relocate_discard_cmd(dcc, dc);
>>> +			retry = true;
>>> +		}
>>> +		spin_unlock_irqrestore(&dc->lock, flags);
>>> +	}
>>> +	mutex_unlock(&dcc->cmd_lock);
>>> +
>>> +	return retry;
>>> +}
>>> +
>>>  static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>  					struct discard_policy *dpolicy)
>>>  {
>>> @@ -1470,12 +1518,13 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>  	struct list_head *pend_list;
>>>  	struct discard_cmd *dc, *tmp;
>>>  	struct blk_plug plug;
>>> -	int i, issued = 0;
>>> +	int i, err, issued = 0;
>>>  	bool io_interrupted = false;
>>>  
>>>  	if (dpolicy->timeout != 0)
>>>  		f2fs_update_time(sbi, dpolicy->timeout);
>>>  
>>> +retry:
>>>  	for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
>>>  		if (dpolicy->timeout != 0 &&
>>>  				f2fs_time_over(sbi, dpolicy->timeout))
>>> @@ -1509,7 +1558,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>  				break;
>>>  			}
>>>  
>>> -			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
>>> +			err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
>>> +			if (err == -EAGAIN)
>>> +				congestion_wait(BLK_RW_ASYNC,
>>> +						DEFAULT_IO_TIMEOUT);
>>>  
>>>  			if (issued >= dpolicy->max_requests)
>>>  				break;
>>> @@ -1522,6 +1574,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>  			break;
>>>  	}
>>>  
>>> +	if (!list_empty(&dcc->retry_list) &&
>>> +		__should_discard_retry(sbi, dpolicy))
>>> +		goto retry;
>>> +
>>>  	if (!issued && io_interrupted)
>>>  		issued = -1;
>>>  
>>> @@ -1613,6 +1669,12 @@ static unsigned int __wait_discard_cmd_range(struct f2fs_sb_info *sbi,
>>>  		goto next;
>>>  	}
>>>  
>>> +	if (dpolicy->type == DPOLICY_UMOUNT &&
>>> +		!list_empty(&dcc->retry_list)) {
>>> +		wait_list = &dcc->retry_list;
>>> +		goto next;
>>> +	}
>>> +
>>>  	return trimmed;
>>>  }
>>>  
>>> @@ -2051,6 +2113,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
>>>  	for (i = 0; i < MAX_PLIST_NUM; i++)
>>>  		INIT_LIST_HEAD(&dcc->pend_list[i]);
>>>  	INIT_LIST_HEAD(&dcc->wait_list);
>>> +	INIT_LIST_HEAD(&dcc->retry_list);
>>>  	INIT_LIST_HEAD(&dcc->fstrim_list);
>>>  	mutex_init(&dcc->cmd_lock);
>>>  	atomic_set(&dcc->issued_discard, 0);
>>>
> 

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

Hi Chao,

On Thu, Mar 26, 2020 at 05:00:18PM +0800, Chao Yu wrote:
> Hi Sahitya,
> 
> On 2020/3/18 12:44, Sahitya Tummala wrote:
> > F2FS already has a default timeout of 5 secs for discards that
> > can be issued during umount, but it can take more than the 5 sec
> > timeout if the underlying UFS device queue is already full and there
> > are no more available free tags to be used. In that case, submit_bio()
> > will wait for the already queued discard requests to complete to get
> > a free tag, which can potentially take way more than 5 sec.
> > 
> > Fix this by submitting the discard requests with REQ_NOWAIT
> > flags during umount. This will return -EAGAIN for UFS queue/tag full
> > scenario without waiting in the context of submit_bio(). The FS can
> > then handle these requests by retrying again within the stipulated
> > discard timeout period to avoid long latencies.
> > 
> > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > ---
> > v2:
> > - Handle the case where a dc can have multiple bios associated with it
> > 
> >  fs/f2fs/f2fs.h    |  1 +
> >  fs/f2fs/segment.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++-------
> >  2 files changed, 74 insertions(+), 10 deletions(-)
> > 
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 12a197e..67b8dcc 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -340,6 +340,7 @@ struct discard_cmd_control {
> >  	struct list_head pend_list[MAX_PLIST_NUM];/* store pending entries */
> >  	struct list_head wait_list;		/* store on-flushing entries */
> >  	struct list_head fstrim_list;		/* in-flight discard from fstrim */
> > +	struct list_head retry_list;		/* list of cmds to retry */
> >  	wait_queue_head_t discard_wait_queue;	/* waiting queue for wake-up */
> >  	unsigned int discard_wake;		/* to wake up discard thread */
> >  	struct mutex cmd_lock;
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index fb3e531..4162c76 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -1029,13 +1029,16 @@ static void f2fs_submit_discard_endio(struct bio *bio)
> >  	struct discard_cmd *dc = (struct discard_cmd *)bio->bi_private;
> >  	unsigned long flags;
> >  
> > -	dc->error = blk_status_to_errno(bio->bi_status);
> > -
> >  	spin_lock_irqsave(&dc->lock, flags);
> > +	if (!dc->error)
> > +		dc->error = blk_status_to_errno(bio->bi_status);
> > +
> >  	dc->bio_ref--;
> > -	if (!dc->bio_ref && dc->state == D_SUBMIT) {
> > -		dc->state = D_DONE;
> > -		complete_all(&dc->wait);
> > +	if (!dc->bio_ref) {
> > +		if (dc->error || dc->state == D_SUBMIT) {
> > +			dc->state = D_DONE;
> > +			complete_all(&dc->wait);
> > +		}
> >  	}
> >  	spin_unlock_irqrestore(&dc->lock, flags);
> >  	bio_put(bio);
> > @@ -1124,10 +1127,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> >  					&(dcc->fstrim_list) : &(dcc->wait_list);
> > -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> > -	block_t lstart, start, len, total_len;
> > +	int flag;
> > +	block_t lstart, start, len, total_len, orig_len;
> >  	int err = 0;
> >  
> > +	flag = dpolicy->sync ? REQ_SYNC : 0;
> > +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> > +
> >  	if (dc->state != D_PREP)
> >  		return 0;
> >  
> > @@ -1139,7 +1145,7 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >  	lstart = dc->lstart;
> >  	start = dc->start;
> >  	len = dc->len;
> > -	total_len = len;
> > +	orig_len = total_len = len;
> >  
> >  	dc->len = 0;
> >  
> > @@ -1203,6 +1209,14 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >  		bio->bi_end_io = f2fs_submit_discard_endio;
> >  		bio->bi_opf |= flag;
> >  		submit_bio(bio);
> > +		if (flag & REQ_NOWAIT) {
> > +			if (dc->error == -EAGAIN) {
> > +				dc->len = orig_len;
> > +				list_move(&dc->list, &dcc->retry_list);
> > +				err = dc->error;
> 
> I encounter lots of dmesg, which should be printed by __remove_discard_cmd()
> 
> F2FS-fs (dm-0): Issue discard(23552, 23552, 2) failed, ret: -11
> 
> This should happen only if we didn't handle all discard in 5 seconds during
> umount.
> 
> So I doubt we failed to move dc to retry_list, because after submit_bio(),
> end_io() is not called synchronously as the bio was just pluged?
> 
This can happen if a discard cmd has multiple bios and at least 1 bio is 
already submitted and when submitting other bios, we encounter -EAGAIN.
In this case, this dc will be moved to retry_list and will be moved back
to dcc->pend_list only if the dc->bio_ref becomes 0 within 5 sec timeout.
If it doesn't become zero, then it will be left in retry_list itself, which
will be later removed from retry_list. Before removing from retry_list we 
will however ensure that submitted bio is done i.e., dc->bio_ref is 0, but
dc->error will be -EAGAIN as this dc could not be requeued/retried.

So this is expected, where it only means that this dc could not be
submitted/retried again within timeout. I think we can ignore
this -EAGAIN error in __remove_discard_cmd().

Thanks,

> Thanks,
> 
> > +				break;
> > +			}
> > +		}
> >  
> >  		atomic_inc(&dcc->issued_discard);
> >  
> > @@ -1463,6 +1477,40 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
> >  	return issued;
> >  }
> >  
> > +static bool __should_discard_retry(struct f2fs_sb_info *sbi,
s> > +		struct discard_policy *dpolicy)
> > +{
> > +	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > +	struct discard_cmd *dc, *tmp;
> > +	bool retry = false;
> > +	unsigned long flags;
> > +
> > +	if (dpolicy->type != DPOLICY_UMOUNT)
> > +		f2fs_bug_on(sbi, 1);
> > +
> > +	mutex_lock(&dcc->cmd_lock);
> > +	list_for_each_entry_safe(dc, tmp, &(dcc->retry_list), list) {
> > +		if (dpolicy->timeout != 0 &&
> > +			f2fs_time_over(sbi, dpolicy->timeout)) {
> > +			retry = false;
> > +			break;
> > +		}
> > +
> > +		spin_lock_irqsave(&dc->lock, flags);
> > +		if (!dc->bio_ref) {
> > +			dc->state = D_PREP;
> > +			dc->error = 0;
> > +			reinit_completion(&dc->wait);
> > +			__relocate_discard_cmd(dcc, dc);
> > +			retry = true;
> > +		}
> > +		spin_unlock_irqrestore(&dc->lock, flags);
> > +	}
> > +	mutex_unlock(&dcc->cmd_lock);
> > +
> > +	return retry;
> > +}
> > +
> >  static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >  					struct discard_policy *dpolicy)
> >  {
> > @@ -1470,12 +1518,13 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >  	struct list_head *pend_list;
> >  	struct discard_cmd *dc, *tmp;
> >  	struct blk_plug plug;
> > -	int i, issued = 0;
> > +	int i, err, issued = 0;
> >  	bool io_interrupted = false;
> >  
> >  	if (dpolicy->timeout != 0)
> >  		f2fs_update_time(sbi, dpolicy->timeout);
> >  
> > +retry:
> >  	for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
> >  		if (dpolicy->timeout != 0 &&
> >  				f2fs_time_over(sbi, dpolicy->timeout))
> > @@ -1509,7 +1558,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >  				break;
> >  			}
> >  
> > -			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > +			err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> > +			if (err == -EAGAIN)
> > +				congestion_wait(BLK_RW_ASYNC,
> > +						DEFAULT_IO_TIMEOUT);
> >  
> >  			if (issued >= dpolicy->max_requests)
> >  				break;
> > @@ -1522,6 +1574,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >  			break;
> >  	}
> >  
> > +	if (!list_empty(&dcc->retry_list) &&
> > +		__should_discard_retry(sbi, dpolicy))
> > +		goto retry;
> > +
> >  	if (!issued && io_interrupted)
> >  		issued = -1;
> >  
> > @@ -1613,6 +1669,12 @@ static unsigned int __wait_discard_cmd_range(struct f2fs_sb_info *sbi,
> >  		goto next;
> >  	}
> >  
> > +	if (dpolicy->type == DPOLICY_UMOUNT &&
> > +		!list_empty(&dcc->retry_list)) {
> > +		wait_list = &dcc->retry_list;
> > +		goto next;
> > +	}
> > +
> >  	return trimmed;
> >  }
> >  
> > @@ -2051,6 +2113,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
> >  	for (i = 0; i < MAX_PLIST_NUM; i++)
> >  		INIT_LIST_HEAD(&dcc->pend_list[i]);
> >  	INIT_LIST_HEAD(&dcc->wait_list);
> > +	INIT_LIST_HEAD(&dcc->retry_list);
> >  	INIT_LIST_HEAD(&dcc->fstrim_list);
> >  	mutex_init(&dcc->cmd_lock);
> >  	atomic_set(&dcc->issued_discard, 0);
> > 

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

Hi Sahitya,

On 2020/3/18 12:44, Sahitya Tummala wrote:
> F2FS already has a default timeout of 5 secs for discards that
> can be issued during umount, but it can take more than the 5 sec
> timeout if the underlying UFS device queue is already full and there
> are no more available free tags to be used. In that case, submit_bio()
> will wait for the already queued discard requests to complete to get
> a free tag, which can potentially take way more than 5 sec.
> 
> Fix this by submitting the discard requests with REQ_NOWAIT
> flags during umount. This will return -EAGAIN for UFS queue/tag full
> scenario without waiting in the context of submit_bio(). The FS can
> then handle these requests by retrying again within the stipulated
> discard timeout period to avoid long latencies.
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> ---
> v2:
> - Handle the case where a dc can have multiple bios associated with it
> 
>  fs/f2fs/f2fs.h    |  1 +
>  fs/f2fs/segment.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++-------
>  2 files changed, 74 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 12a197e..67b8dcc 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -340,6 +340,7 @@ struct discard_cmd_control {
>  	struct list_head pend_list[MAX_PLIST_NUM];/* store pending entries */
>  	struct list_head wait_list;		/* store on-flushing entries */
>  	struct list_head fstrim_list;		/* in-flight discard from fstrim */
> +	struct list_head retry_list;		/* list of cmds to retry */
>  	wait_queue_head_t discard_wait_queue;	/* waiting queue for wake-up */
>  	unsigned int discard_wake;		/* to wake up discard thread */
>  	struct mutex cmd_lock;
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index fb3e531..4162c76 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1029,13 +1029,16 @@ static void f2fs_submit_discard_endio(struct bio *bio)
>  	struct discard_cmd *dc = (struct discard_cmd *)bio->bi_private;
>  	unsigned long flags;
>  
> -	dc->error = blk_status_to_errno(bio->bi_status);
> -
>  	spin_lock_irqsave(&dc->lock, flags);
> +	if (!dc->error)
> +		dc->error = blk_status_to_errno(bio->bi_status);
> +
>  	dc->bio_ref--;
> -	if (!dc->bio_ref && dc->state == D_SUBMIT) {
> -		dc->state = D_DONE;
> -		complete_all(&dc->wait);
> +	if (!dc->bio_ref) {
> +		if (dc->error || dc->state == D_SUBMIT) {
> +			dc->state = D_DONE;
> +			complete_all(&dc->wait);
> +		}
>  	}
>  	spin_unlock_irqrestore(&dc->lock, flags);
>  	bio_put(bio);
> @@ -1124,10 +1127,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> -	int flag = dpolicy->sync ? REQ_SYNC : 0;
> -	block_t lstart, start, len, total_len;
> +	int flag;
> +	block_t lstart, start, len, total_len, orig_len;
>  	int err = 0;
>  
> +	flag = dpolicy->sync ? REQ_SYNC : 0;
> +	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
> +
>  	if (dc->state != D_PREP)
>  		return 0;
>  
> @@ -1139,7 +1145,7 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  	lstart = dc->lstart;
>  	start = dc->start;
>  	len = dc->len;
> -	total_len = len;
> +	orig_len = total_len = len;
>  
>  	dc->len = 0;
>  
> @@ -1203,6 +1209,14 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  		bio->bi_end_io = f2fs_submit_discard_endio;
>  		bio->bi_opf |= flag;
>  		submit_bio(bio);
> +		if (flag & REQ_NOWAIT) {
> +			if (dc->error == -EAGAIN) {
> +				dc->len = orig_len;
> +				list_move(&dc->list, &dcc->retry_list);
> +				err = dc->error;

I encounter lots of dmesg, which should be printed by __remove_discard_cmd()

F2FS-fs (dm-0): Issue discard(23552, 23552, 2) failed, ret: -11

This should happen only if we didn't handle all discard in 5 seconds during
umount.

So I doubt we failed to move dc to retry_list, because after submit_bio(),
end_io() is not called synchronously as the bio was just pluged?

Thanks,

> +				break;
> +			}
> +		}
>  
>  		atomic_inc(&dcc->issued_discard);
>  
> @@ -1463,6 +1477,40 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
>  	return issued;
>  }
>  
> +static bool __should_discard_retry(struct f2fs_sb_info *sbi,
> +		struct discard_policy *dpolicy)
> +{
> +	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> +	struct discard_cmd *dc, *tmp;
> +	bool retry = false;
> +	unsigned long flags;
> +
> +	if (dpolicy->type != DPOLICY_UMOUNT)
> +		f2fs_bug_on(sbi, 1);
> +
> +	mutex_lock(&dcc->cmd_lock);
> +	list_for_each_entry_safe(dc, tmp, &(dcc->retry_list), list) {
> +		if (dpolicy->timeout != 0 &&
> +			f2fs_time_over(sbi, dpolicy->timeout)) {
> +			retry = false;
> +			break;
> +		}
> +
> +		spin_lock_irqsave(&dc->lock, flags);
> +		if (!dc->bio_ref) {
> +			dc->state = D_PREP;
> +			dc->error = 0;
> +			reinit_completion(&dc->wait);
> +			__relocate_discard_cmd(dcc, dc);
> +			retry = true;
> +		}
> +		spin_unlock_irqrestore(&dc->lock, flags);
> +	}
> +	mutex_unlock(&dcc->cmd_lock);
> +
> +	return retry;
> +}
> +
>  static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  					struct discard_policy *dpolicy)
>  {
> @@ -1470,12 +1518,13 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  	struct list_head *pend_list;
>  	struct discard_cmd *dc, *tmp;
>  	struct blk_plug plug;
> -	int i, issued = 0;
> +	int i, err, issued = 0;
>  	bool io_interrupted = false;
>  
>  	if (dpolicy->timeout != 0)
>  		f2fs_update_time(sbi, dpolicy->timeout);
>  
> +retry:
>  	for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
>  		if (dpolicy->timeout != 0 &&
>  				f2fs_time_over(sbi, dpolicy->timeout))
> @@ -1509,7 +1558,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  				break;
>  			}
>  
> -			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
> +			err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> +			if (err == -EAGAIN)
> +				congestion_wait(BLK_RW_ASYNC,
> +						DEFAULT_IO_TIMEOUT);
>  
>  			if (issued >= dpolicy->max_requests)
>  				break;
> @@ -1522,6 +1574,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  			break;
>  	}
>  
> +	if (!list_empty(&dcc->retry_list) &&
> +		__should_discard_retry(sbi, dpolicy))
> +		goto retry;
> +
>  	if (!issued && io_interrupted)
>  		issued = -1;
>  
> @@ -1613,6 +1669,12 @@ static unsigned int __wait_discard_cmd_range(struct f2fs_sb_info *sbi,
>  		goto next;
>  	}
>  
> +	if (dpolicy->type == DPOLICY_UMOUNT &&
> +		!list_empty(&dcc->retry_list)) {
> +		wait_list = &dcc->retry_list;
> +		goto next;
> +	}
> +
>  	return trimmed;
>  }
>  
> @@ -2051,6 +2113,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
>  	for (i = 0; i < MAX_PLIST_NUM; i++)
>  		INIT_LIST_HEAD(&dcc->pend_list[i]);
>  	INIT_LIST_HEAD(&dcc->wait_list);
> +	INIT_LIST_HEAD(&dcc->retry_list);
>  	INIT_LIST_HEAD(&dcc->fstrim_list);
>  	mutex_init(&dcc->cmd_lock);
>  	atomic_set(&dcc->issued_discard, 0);
> 

Re: [PATCH] f2fs: fix long latency due to discard during umount

[Chao Yu]

On 2020/3/18 12:44, Sahitya Tummala wrote:
> F2FS already has a default timeout of 5 secs for discards that
> can be issued during umount, but it can take more than the 5 sec
> timeout if the underlying UFS device queue is already full and there
> are no more available free tags to be used. In that case, submit_bio()
> will wait for the already queued discard requests to complete to get
> a free tag, which can potentially take way more than 5 sec.
> 
> Fix this by submitting the discard requests with REQ_NOWAIT
> flags during umount. This will return -EAGAIN for UFS queue/tag full
> scenario without waiting in the context of submit_bio(). The FS can
> then handle these requests by retrying again within the stipulated
> discard timeout period to avoid long latencies.
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,

[PATCH] f2fs: fix long latency due to discard during umount

[Sahitya Tummala]

F2FS already has a default timeout of 5 secs for discards that
can be issued during umount, but it can take more than the 5 sec
timeout if the underlying UFS device queue is already full and there
are no more available free tags to be used. In that case, submit_bio()
will wait for the already queued discard requests to complete to get
a free tag, which can potentially take way more than 5 sec.

Fix this by submitting the discard requests with REQ_NOWAIT
flags during umount. This will return -EAGAIN for UFS queue/tag full
scenario without waiting in the context of submit_bio(). The FS can
then handle these requests by retrying again within the stipulated
discard timeout period to avoid long latencies.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
---
v2:
- Handle the case where a dc can have multiple bios associated with it

 fs/f2fs/f2fs.h    |  1 +
 fs/f2fs/segment.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 74 insertions(+), 10 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 12a197e..67b8dcc 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -340,6 +340,7 @@ struct discard_cmd_control {
 	struct list_head pend_list[MAX_PLIST_NUM];/* store pending entries */
 	struct list_head wait_list;		/* store on-flushing entries */
 	struct list_head fstrim_list;		/* in-flight discard from fstrim */
+	struct list_head retry_list;		/* list of cmds to retry */
 	wait_queue_head_t discard_wait_queue;	/* waiting queue for wake-up */
 	unsigned int discard_wake;		/* to wake up discard thread */
 	struct mutex cmd_lock;
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index fb3e531..4162c76 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1029,13 +1029,16 @@ static void f2fs_submit_discard_endio(struct bio *bio)
 	struct discard_cmd *dc = (struct discard_cmd *)bio->bi_private;
 	unsigned long flags;
 
-	dc->error = blk_status_to_errno(bio->bi_status);
-
 	spin_lock_irqsave(&dc->lock, flags);
+	if (!dc->error)
+		dc->error = blk_status_to_errno(bio->bi_status);
+
 	dc->bio_ref--;
-	if (!dc->bio_ref && dc->state == D_SUBMIT) {
-		dc->state = D_DONE;
-		complete_all(&dc->wait);
+	if (!dc->bio_ref) {
+		if (dc->error || dc->state == D_SUBMIT) {
+			dc->state = D_DONE;
+			complete_all(&dc->wait);
+		}
 	}
 	spin_unlock_irqrestore(&dc->lock, flags);
 	bio_put(bio);
@@ -1124,10 +1127,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
 	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
 	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
 					&(dcc->fstrim_list) : &(dcc->wait_list);
-	int flag = dpolicy->sync ? REQ_SYNC : 0;
-	block_t lstart, start, len, total_len;
+	int flag;
+	block_t lstart, start, len, total_len, orig_len;
 	int err = 0;
 
+	flag = dpolicy->sync ? REQ_SYNC : 0;
+	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
+
 	if (dc->state != D_PREP)
 		return 0;
 
@@ -1139,7 +1145,7 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
 	lstart = dc->lstart;
 	start = dc->start;
 	len = dc->len;
-	total_len = len;
+	orig_len = total_len = len;
 
 	dc->len = 0;
 
@@ -1203,6 +1209,14 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
 		bio->bi_end_io = f2fs_submit_discard_endio;
 		bio->bi_opf |= flag;
 		submit_bio(bio);
+		if (flag & REQ_NOWAIT) {
+			if (dc->error == -EAGAIN) {
+				dc->len = orig_len;
+				list_move(&dc->list, &dcc->retry_list);
+				err = dc->error;
+				break;
+			}
+		}
 
 		atomic_inc(&dcc->issued_discard);
 
@@ -1463,6 +1477,40 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
 	return issued;
 }
 
+static bool __should_discard_retry(struct f2fs_sb_info *sbi,
+		struct discard_policy *dpolicy)
+{
+	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
+	struct discard_cmd *dc, *tmp;
+	bool retry = false;
+	unsigned long flags;
+
+	if (dpolicy->type != DPOLICY_UMOUNT)
+		f2fs_bug_on(sbi, 1);
+
+	mutex_lock(&dcc->cmd_lock);
+	list_for_each_entry_safe(dc, tmp, &(dcc->retry_list), list) {
+		if (dpolicy->timeout != 0 &&
+			f2fs_time_over(sbi, dpolicy->timeout)) {
+			retry = false;
+			break;
+		}
+
+		spin_lock_irqsave(&dc->lock, flags);
+		if (!dc->bio_ref) {
+			dc->state = D_PREP;
+			dc->error = 0;
+			reinit_completion(&dc->wait);
+			__relocate_discard_cmd(dcc, dc);
+			retry = true;
+		}
+		spin_unlock_irqrestore(&dc->lock, flags);
+	}
+	mutex_unlock(&dcc->cmd_lock);
+
+	return retry;
+}
+
 static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 					struct discard_policy *dpolicy)
 {
@@ -1470,12 +1518,13 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 	struct list_head *pend_list;
 	struct discard_cmd *dc, *tmp;
 	struct blk_plug plug;
-	int i, issued = 0;
+	int i, err, issued = 0;
 	bool io_interrupted = false;
 
 	if (dpolicy->timeout != 0)
 		f2fs_update_time(sbi, dpolicy->timeout);
 
+retry:
 	for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
 		if (dpolicy->timeout != 0 &&
 				f2fs_time_over(sbi, dpolicy->timeout))
@@ -1509,7 +1558,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 				break;
 			}
 
-			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
+			err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
+			if (err == -EAGAIN)
+				congestion_wait(BLK_RW_ASYNC,
+						DEFAULT_IO_TIMEOUT);
 
 			if (issued >= dpolicy->max_requests)
 				break;
@@ -1522,6 +1574,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 			break;
 	}
 
+	if (!list_empty(&dcc->retry_list) &&
+		__should_discard_retry(sbi, dpolicy))
+		goto retry;
+
 	if (!issued && io_interrupted)
 		issued = -1;
 
@@ -1613,6 +1669,12 @@ static unsigned int __wait_discard_cmd_range(struct f2fs_sb_info *sbi,
 		goto next;
 	}
 
+	if (dpolicy->type == DPOLICY_UMOUNT &&
+		!list_empty(&dcc->retry_list)) {
+		wait_list = &dcc->retry_list;
+		goto next;
+	}
+
 	return trimmed;
 }
 
@@ -2051,6 +2113,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
 	for (i = 0; i < MAX_PLIST_NUM; i++)
 		INIT_LIST_HEAD(&dcc->pend_list[i]);
 	INIT_LIST_HEAD(&dcc->wait_list);
+	INIT_LIST_HEAD(&dcc->retry_list);
 	INIT_LIST_HEAD(&dcc->fstrim_list);
 	mutex_init(&dcc->cmd_lock);
 	atomic_set(&dcc->issued_discard, 0);
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.