f2fs: remove a waiter for checkpoint completion
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Message ID 20200803172825.4077289-1-jaegeuk@kernel.org
State In Next
Commit efbb0ef0d963c93decc3626ff8786429cbf173ec
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Series
  • f2fs: remove a waiter for checkpoint completion
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Commit Message

Jaegeuk Kim Aug. 3, 2020, 5:28 p.m. UTC
It doesn't need to wait for checkpoint being completed triggered by end_io.

[   20.157753] ------------[ cut here ]------------
[   20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430
[   20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0
...
[   20.176110]  __submit_merged_write_cond+0x191/0x310
[   20.176739]  f2fs_submit_merged_write+0x18/0x20
[   20.177323]  f2fs_wait_on_all_pages+0x269/0x2d0
[   20.177899]  ? block_operations+0x980/0x980
[   20.178441]  ? __kasan_check_read+0x11/0x20
[   20.178975]  ? finish_wait+0x260/0x260
[   20.179488]  ? percpu_counter_set+0x147/0x230
[   20.180049]  do_checkpoint+0x1757/0x2a50
[   20.180558]  f2fs_write_checkpoint+0x840/0xaf0
[   20.181126]  f2fs_sync_fs+0x287/0x4a0

Reported-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 fs/f2fs/checkpoint.c | 6 +-----
 fs/f2fs/data.c       | 4 ----
 fs/f2fs/f2fs.h       | 1 -
 fs/f2fs/super.c      | 1 -
 4 files changed, 1 insertion(+), 11 deletions(-)

Comments

Chao Yu Aug. 4, 2020, 12:55 a.m. UTC | #1
On 2020/8/4 1:28, Jaegeuk Kim wrote:
> It doesn't need to wait for checkpoint being completed triggered by end_io.
> 
> [   20.157753] ------------[ cut here ]------------
> [   20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430
> [   20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0
> ...
> [   20.176110]  __submit_merged_write_cond+0x191/0x310
> [   20.176739]  f2fs_submit_merged_write+0x18/0x20
> [   20.177323]  f2fs_wait_on_all_pages+0x269/0x2d0
> [   20.177899]  ? block_operations+0x980/0x980
> [   20.178441]  ? __kasan_check_read+0x11/0x20
> [   20.178975]  ? finish_wait+0x260/0x260
> [   20.179488]  ? percpu_counter_set+0x147/0x230
> [   20.180049]  do_checkpoint+0x1757/0x2a50
> [   20.180558]  f2fs_write_checkpoint+0x840/0xaf0
> [   20.181126]  f2fs_sync_fs+0x287/0x4a0
> 
> Reported-by: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>   fs/f2fs/checkpoint.c | 6 +-----
>   fs/f2fs/data.c       | 4 ----
>   fs/f2fs/f2fs.h       | 1 -
>   fs/f2fs/super.c      | 1 -
>   4 files changed, 1 insertion(+), 11 deletions(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 99c8061da55b9..2bdddc725e677 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -1255,11 +1255,7 @@ static void unblock_operations(struct f2fs_sb_info *sbi)
>   
>   void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>   {
> -	DEFINE_WAIT(wait);
> -
>   	for (;;) {
> -		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);

Wouldn't that case high cpu usage before io end?

> -
>   		if (!get_pages(sbi, type))
>   			break;
>   
> @@ -1271,9 +1267,9 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>   							FS_CP_META_IO);
>   		else if (type == F2FS_WB_CP_DATA)
>   			f2fs_submit_merged_write(sbi, DATA);
> +
>   		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
>   	}
> -	finish_wait(&sbi->cp_wait, &wait);
>   }
>   
>   static void update_ckpt_flags(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index c1b676be67b9a..588d2871bbe69 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -383,10 +383,6 @@ static void f2fs_write_end_io(struct bio *bio)
>   		clear_cold_data(page);
>   		end_page_writeback(page);
>   	}
> -	if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
> -				wq_has_sleeper(&sbi->cp_wait))
> -		wake_up(&sbi->cp_wait);
> -
>   	bio_put(bio);
>   }
>   
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 02811ce15059b..a036539363030 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1437,7 +1437,6 @@ struct f2fs_sb_info {
>   	struct rw_semaphore cp_rwsem;		/* blocking FS operations */
>   	struct rw_semaphore node_write;		/* locking node writes */
>   	struct rw_semaphore node_change;	/* locking node change */
> -	wait_queue_head_t cp_wait;
>   	unsigned long last_time[MAX_TIME];	/* to store time in jiffies */
>   	long interval_time[MAX_TIME];		/* to store thresholds */
>   
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 83bf9a02f83f2..5f4d9abc079d6 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -3540,7 +3540,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>   
>   	init_rwsem(&sbi->cp_rwsem);
>   	init_rwsem(&sbi->quota_sem);
> -	init_waitqueue_head(&sbi->cp_wait);
>   	init_sb_info(sbi);
>   
>   	err = init_percpu_info(sbi);
>
Jaegeuk Kim Aug. 4, 2020, 1:04 a.m. UTC | #2
On 08/04, Chao Yu wrote:
> On 2020/8/4 1:28, Jaegeuk Kim wrote:
> > It doesn't need to wait for checkpoint being completed triggered by end_io.
> > 
> > [   20.157753] ------------[ cut here ]------------
> > [   20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430
> > [   20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0
> > ...
> > [   20.176110]  __submit_merged_write_cond+0x191/0x310
> > [   20.176739]  f2fs_submit_merged_write+0x18/0x20
> > [   20.177323]  f2fs_wait_on_all_pages+0x269/0x2d0
> > [   20.177899]  ? block_operations+0x980/0x980
> > [   20.178441]  ? __kasan_check_read+0x11/0x20
> > [   20.178975]  ? finish_wait+0x260/0x260
> > [   20.179488]  ? percpu_counter_set+0x147/0x230
> > [   20.180049]  do_checkpoint+0x1757/0x2a50
> > [   20.180558]  f2fs_write_checkpoint+0x840/0xaf0
> > [   20.181126]  f2fs_sync_fs+0x287/0x4a0
> > 
> > Reported-by: Eric Biggers <ebiggers@kernel.org>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> >   fs/f2fs/checkpoint.c | 6 +-----
> >   fs/f2fs/data.c       | 4 ----
> >   fs/f2fs/f2fs.h       | 1 -
> >   fs/f2fs/super.c      | 1 -
> >   4 files changed, 1 insertion(+), 11 deletions(-)
> > 
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index 99c8061da55b9..2bdddc725e677 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -1255,11 +1255,7 @@ static void unblock_operations(struct f2fs_sb_info *sbi)
> >   void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
> >   {
> > -	DEFINE_WAIT(wait);
> > -
> >   	for (;;) {
> > -		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
> 
> Wouldn't that case high cpu usage before io end?

This is a critical path to wait for IO completion in checkpoint, which would be
better to wait for it to avoid long latency to continue filesystem operations.
Moreover, I expect io_schedule_timeout() can mitigate such the CPU overhead and
actually we don't need to make there-in context switches as well.

> 
> > -
> >   		if (!get_pages(sbi, type))
> >   			break;
> > @@ -1271,9 +1267,9 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
> >   							FS_CP_META_IO);
> >   		else if (type == F2FS_WB_CP_DATA)
> >   			f2fs_submit_merged_write(sbi, DATA);
> > +
> >   		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
> >   	}
> > -	finish_wait(&sbi->cp_wait, &wait);
> >   }
> >   static void update_ckpt_flags(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index c1b676be67b9a..588d2871bbe69 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -383,10 +383,6 @@ static void f2fs_write_end_io(struct bio *bio)
> >   		clear_cold_data(page);
> >   		end_page_writeback(page);
> >   	}
> > -	if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
> > -				wq_has_sleeper(&sbi->cp_wait))
> > -		wake_up(&sbi->cp_wait);
> > -
> >   	bio_put(bio);
> >   }
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 02811ce15059b..a036539363030 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -1437,7 +1437,6 @@ struct f2fs_sb_info {
> >   	struct rw_semaphore cp_rwsem;		/* blocking FS operations */
> >   	struct rw_semaphore node_write;		/* locking node writes */
> >   	struct rw_semaphore node_change;	/* locking node change */
> > -	wait_queue_head_t cp_wait;
> >   	unsigned long last_time[MAX_TIME];	/* to store time in jiffies */
> >   	long interval_time[MAX_TIME];		/* to store thresholds */
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > index 83bf9a02f83f2..5f4d9abc079d6 100644
> > --- a/fs/f2fs/super.c
> > +++ b/fs/f2fs/super.c
> > @@ -3540,7 +3540,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
> >   	init_rwsem(&sbi->cp_rwsem);
> >   	init_rwsem(&sbi->quota_sem);
> > -	init_waitqueue_head(&sbi->cp_wait);
> >   	init_sb_info(sbi);
> >   	err = init_percpu_info(sbi);
> >
Chao Yu Aug. 4, 2020, 1:17 a.m. UTC | #3
On 2020/8/4 9:04, Jaegeuk Kim wrote:
> On 08/04, Chao Yu wrote:
>> On 2020/8/4 1:28, Jaegeuk Kim wrote:
>>> It doesn't need to wait for checkpoint being completed triggered by end_io.
>>>
>>> [   20.157753] ------------[ cut here ]------------
>>> [   20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430
>>> [   20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0
>>> ...
>>> [   20.176110]  __submit_merged_write_cond+0x191/0x310
>>> [   20.176739]  f2fs_submit_merged_write+0x18/0x20
>>> [   20.177323]  f2fs_wait_on_all_pages+0x269/0x2d0
>>> [   20.177899]  ? block_operations+0x980/0x980
>>> [   20.178441]  ? __kasan_check_read+0x11/0x20
>>> [   20.178975]  ? finish_wait+0x260/0x260
>>> [   20.179488]  ? percpu_counter_set+0x147/0x230
>>> [   20.180049]  do_checkpoint+0x1757/0x2a50
>>> [   20.180558]  f2fs_write_checkpoint+0x840/0xaf0
>>> [   20.181126]  f2fs_sync_fs+0x287/0x4a0
>>>
>>> Reported-by: Eric Biggers <ebiggers@kernel.org>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>> ---
>>>    fs/f2fs/checkpoint.c | 6 +-----
>>>    fs/f2fs/data.c       | 4 ----
>>>    fs/f2fs/f2fs.h       | 1 -
>>>    fs/f2fs/super.c      | 1 -
>>>    4 files changed, 1 insertion(+), 11 deletions(-)
>>>
>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>> index 99c8061da55b9..2bdddc725e677 100644
>>> --- a/fs/f2fs/checkpoint.c
>>> +++ b/fs/f2fs/checkpoint.c
>>> @@ -1255,11 +1255,7 @@ static void unblock_operations(struct f2fs_sb_info *sbi)
>>>    void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>>>    {
>>> -	DEFINE_WAIT(wait);
>>> -
>>>    	for (;;) {
>>> -		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
>>
>> Wouldn't that case high cpu usage before io end?
> 
> This is a critical path to wait for IO completion in checkpoint, which would be
> better to wait for it to avoid long latency to continue filesystem operations.

Yup, in previous implementation, last end_io wakes up checkpoint() waiter, we
didn't waste any time there.

> Moreover, I expect io_schedule_timeout() can mitigate such the CPU overhead and
> actually we don't need to make there-in context switches as well.

Then io_schedule_timeout() in this loop may give CPU time slice to other thread
until scheduler reselect checkpoint(), that would cause longer latency?

> 
>>
>>> -
>>>    		if (!get_pages(sbi, type))
>>>    			break;
>>> @@ -1271,9 +1267,9 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>>>    							FS_CP_META_IO);
>>>    		else if (type == F2FS_WB_CP_DATA)
>>>    			f2fs_submit_merged_write(sbi, DATA);
>>> +
>>>    		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
>>>    	}
>>> -	finish_wait(&sbi->cp_wait, &wait);
>>>    }
>>>    static void update_ckpt_flags(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index c1b676be67b9a..588d2871bbe69 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -383,10 +383,6 @@ static void f2fs_write_end_io(struct bio *bio)
>>>    		clear_cold_data(page);
>>>    		end_page_writeback(page);
>>>    	}
>>> -	if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
>>> -				wq_has_sleeper(&sbi->cp_wait))
>>> -		wake_up(&sbi->cp_wait);
>>> -
>>>    	bio_put(bio);
>>>    }
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 02811ce15059b..a036539363030 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -1437,7 +1437,6 @@ struct f2fs_sb_info {
>>>    	struct rw_semaphore cp_rwsem;		/* blocking FS operations */
>>>    	struct rw_semaphore node_write;		/* locking node writes */
>>>    	struct rw_semaphore node_change;	/* locking node change */
>>> -	wait_queue_head_t cp_wait;
>>>    	unsigned long last_time[MAX_TIME];	/* to store time in jiffies */
>>>    	long interval_time[MAX_TIME];		/* to store thresholds */
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>> index 83bf9a02f83f2..5f4d9abc079d6 100644
>>> --- a/fs/f2fs/super.c
>>> +++ b/fs/f2fs/super.c
>>> @@ -3540,7 +3540,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>>>    	init_rwsem(&sbi->cp_rwsem);
>>>    	init_rwsem(&sbi->quota_sem);
>>> -	init_waitqueue_head(&sbi->cp_wait);
>>>    	init_sb_info(sbi);
>>>    	err = init_percpu_info(sbi);
>>>
> .
>
Jaegeuk Kim Aug. 4, 2020, 2:43 a.m. UTC | #4
On 08/04, Chao Yu wrote:
> On 2020/8/4 9:04, Jaegeuk Kim wrote:
> > On 08/04, Chao Yu wrote:
> > > On 2020/8/4 1:28, Jaegeuk Kim wrote:
> > > > It doesn't need to wait for checkpoint being completed triggered by end_io.
> > > > 
> > > > [   20.157753] ------------[ cut here ]------------
> > > > [   20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430
> > > > [   20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0
> > > > ...
> > > > [   20.176110]  __submit_merged_write_cond+0x191/0x310
> > > > [   20.176739]  f2fs_submit_merged_write+0x18/0x20
> > > > [   20.177323]  f2fs_wait_on_all_pages+0x269/0x2d0
> > > > [   20.177899]  ? block_operations+0x980/0x980
> > > > [   20.178441]  ? __kasan_check_read+0x11/0x20
> > > > [   20.178975]  ? finish_wait+0x260/0x260
> > > > [   20.179488]  ? percpu_counter_set+0x147/0x230
> > > > [   20.180049]  do_checkpoint+0x1757/0x2a50
> > > > [   20.180558]  f2fs_write_checkpoint+0x840/0xaf0
> > > > [   20.181126]  f2fs_sync_fs+0x287/0x4a0
> > > > 
> > > > Reported-by: Eric Biggers <ebiggers@kernel.org>
> > > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > > > ---
> > > >    fs/f2fs/checkpoint.c | 6 +-----
> > > >    fs/f2fs/data.c       | 4 ----
> > > >    fs/f2fs/f2fs.h       | 1 -
> > > >    fs/f2fs/super.c      | 1 -
> > > >    4 files changed, 1 insertion(+), 11 deletions(-)
> > > > 
> > > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > > > index 99c8061da55b9..2bdddc725e677 100644
> > > > --- a/fs/f2fs/checkpoint.c
> > > > +++ b/fs/f2fs/checkpoint.c
> > > > @@ -1255,11 +1255,7 @@ static void unblock_operations(struct f2fs_sb_info *sbi)
> > > >    void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
> > > >    {
> > > > -	DEFINE_WAIT(wait);
> > > > -
> > > >    	for (;;) {
> > > > -		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
> > > 
> > > Wouldn't that case high cpu usage before io end?
> > 
> > This is a critical path to wait for IO completion in checkpoint, which would be
> > better to wait for it to avoid long latency to continue filesystem operations.
> 
> Yup, in previous implementation, last end_io wakes up checkpoint() waiter, we
> didn't waste any time there.
> 
> > Moreover, I expect io_schedule_timeout() can mitigate such the CPU overhead and
> > actually we don't need to make there-in context switches as well.
> 
> Then io_schedule_timeout() in this loop may give CPU time slice to other thread
> until scheduler reselect checkpoint(), that would cause longer latency?

Hmm, how about this then?

From 4956afa1cedc019cabf6e8bff7bc48d3bcf7a3f5 Mon Sep 17 00:00:00 2001
From: Jaegeuk Kim <jaegeuk@kernel.org>
Date: Mon, 3 Aug 2020 19:37:12 -0700
Subject: [PATCH] f2fs: prepare a waiter before entering io_schedule

This is to avoid sleep() in the waiter thread.

[   20.157753] ------------[ cut here ]------------
[   20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430
[   20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0
...
[   20.176110]  __submit_merged_write_cond+0x191/0x310
[   20.176739]  f2fs_submit_merged_write+0x18/0x20
[   20.177323]  f2fs_wait_on_all_pages+0x269/0x2d0
[   20.177899]  ? block_operations+0x980/0x980
[   20.178441]  ? __kasan_check_read+0x11/0x20
[   20.178975]  ? finish_wait+0x260/0x260
[   20.179488]  ? percpu_counter_set+0x147/0x230
[   20.180049]  do_checkpoint+0x1757/0x2a50
[   20.180558]  f2fs_write_checkpoint+0x840/0xaf0
[   20.181126]  f2fs_sync_fs+0x287/0x4a0

Reported-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 fs/f2fs/checkpoint.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 99c8061da55b9..ff807e14c8911 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1258,8 +1258,6 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
 	DEFINE_WAIT(wait);
 
 	for (;;) {
-		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
-
 		if (!get_pages(sbi, type))
 			break;
 
@@ -1271,6 +1269,8 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
 							FS_CP_META_IO);
 		else if (type == F2FS_WB_CP_DATA)
 			f2fs_submit_merged_write(sbi, DATA);
+
+		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
 		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
 	}
 	finish_wait(&sbi->cp_wait, &wait);
Chao Yu Aug. 4, 2020, 3 a.m. UTC | #5
On 2020/8/4 10:43, Jaegeuk Kim wrote:
> On 08/04, Chao Yu wrote:
>> On 2020/8/4 9:04, Jaegeuk Kim wrote:
>>> On 08/04, Chao Yu wrote:
>>>> On 2020/8/4 1:28, Jaegeuk Kim wrote:
>>>>> It doesn't need to wait for checkpoint being completed triggered by end_io.
>>>>>
>>>>> [   20.157753] ------------[ cut here ]------------
>>>>> [   20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430
>>>>> [   20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0
>>>>> ...
>>>>> [   20.176110]  __submit_merged_write_cond+0x191/0x310
>>>>> [   20.176739]  f2fs_submit_merged_write+0x18/0x20
>>>>> [   20.177323]  f2fs_wait_on_all_pages+0x269/0x2d0
>>>>> [   20.177899]  ? block_operations+0x980/0x980
>>>>> [   20.178441]  ? __kasan_check_read+0x11/0x20
>>>>> [   20.178975]  ? finish_wait+0x260/0x260
>>>>> [   20.179488]  ? percpu_counter_set+0x147/0x230
>>>>> [   20.180049]  do_checkpoint+0x1757/0x2a50
>>>>> [   20.180558]  f2fs_write_checkpoint+0x840/0xaf0
>>>>> [   20.181126]  f2fs_sync_fs+0x287/0x4a0
>>>>>
>>>>> Reported-by: Eric Biggers <ebiggers@kernel.org>
>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>>>> ---
>>>>>     fs/f2fs/checkpoint.c | 6 +-----
>>>>>     fs/f2fs/data.c       | 4 ----
>>>>>     fs/f2fs/f2fs.h       | 1 -
>>>>>     fs/f2fs/super.c      | 1 -
>>>>>     4 files changed, 1 insertion(+), 11 deletions(-)
>>>>>
>>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>>>> index 99c8061da55b9..2bdddc725e677 100644
>>>>> --- a/fs/f2fs/checkpoint.c
>>>>> +++ b/fs/f2fs/checkpoint.c
>>>>> @@ -1255,11 +1255,7 @@ static void unblock_operations(struct f2fs_sb_info *sbi)
>>>>>     void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>>>>>     {
>>>>> -	DEFINE_WAIT(wait);
>>>>> -
>>>>>     	for (;;) {
>>>>> -		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
>>>>
>>>> Wouldn't that case high cpu usage before io end?
>>>
>>> This is a critical path to wait for IO completion in checkpoint, which would be
>>> better to wait for it to avoid long latency to continue filesystem operations.
>>
>> Yup, in previous implementation, last end_io wakes up checkpoint() waiter, we
>> didn't waste any time there.
>>
>>> Moreover, I expect io_schedule_timeout() can mitigate such the CPU overhead and
>>> actually we don't need to make there-in context switches as well.
>>
>> Then io_schedule_timeout() in this loop may give CPU time slice to other thread
>> until scheduler reselect checkpoint(), that would cause longer latency?
> 
> Hmm, how about this then?
> 
>>From 4956afa1cedc019cabf6e8bff7bc48d3bcf7a3f5 Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk@kernel.org>
> Date: Mon, 3 Aug 2020 19:37:12 -0700
> Subject: [PATCH] f2fs: prepare a waiter before entering io_schedule
> 
> This is to avoid sleep() in the waiter thread.
> 
> [   20.157753] ------------[ cut here ]------------
> [   20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430
> [   20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0
> ...
> [   20.176110]  __submit_merged_write_cond+0x191/0x310
> [   20.176739]  f2fs_submit_merged_write+0x18/0x20
> [   20.177323]  f2fs_wait_on_all_pages+0x269/0x2d0
> [   20.177899]  ? block_operations+0x980/0x980
> [   20.178441]  ? __kasan_check_read+0x11/0x20
> [   20.178975]  ? finish_wait+0x260/0x260
> [   20.179488]  ? percpu_counter_set+0x147/0x230
> [   20.180049]  do_checkpoint+0x1757/0x2a50
> [   20.180558]  f2fs_write_checkpoint+0x840/0xaf0
> [   20.181126]  f2fs_sync_fs+0x287/0x4a0
> 
> Reported-by: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Better,

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

Thanks,

> ---
>   fs/f2fs/checkpoint.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 99c8061da55b9..ff807e14c8911 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -1258,8 +1258,6 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>   	DEFINE_WAIT(wait);
>   
>   	for (;;) {
> -		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
> -
>   		if (!get_pages(sbi, type))
>   			break;
>   
> @@ -1271,6 +1269,8 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
>   							FS_CP_META_IO);
>   		else if (type == F2FS_WB_CP_DATA)
>   			f2fs_submit_merged_write(sbi, DATA);
> +
> +		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
>   		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
>   	}
>   	finish_wait(&sbi->cp_wait, &wait);
>

Patch
diff mbox series

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 99c8061da55b9..2bdddc725e677 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1255,11 +1255,7 @@  static void unblock_operations(struct f2fs_sb_info *sbi)
 
 void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
 {
-	DEFINE_WAIT(wait);
-
 	for (;;) {
-		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
-
 		if (!get_pages(sbi, type))
 			break;
 
@@ -1271,9 +1267,9 @@  void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
 							FS_CP_META_IO);
 		else if (type == F2FS_WB_CP_DATA)
 			f2fs_submit_merged_write(sbi, DATA);
+
 		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
 	}
-	finish_wait(&sbi->cp_wait, &wait);
 }
 
 static void update_ckpt_flags(struct f2fs_sb_info *sbi, struct cp_control *cpc)
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index c1b676be67b9a..588d2871bbe69 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -383,10 +383,6 @@  static void f2fs_write_end_io(struct bio *bio)
 		clear_cold_data(page);
 		end_page_writeback(page);
 	}
-	if (!get_pages(sbi, F2FS_WB_CP_DATA) &&
-				wq_has_sleeper(&sbi->cp_wait))
-		wake_up(&sbi->cp_wait);
-
 	bio_put(bio);
 }
 
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 02811ce15059b..a036539363030 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1437,7 +1437,6 @@  struct f2fs_sb_info {
 	struct rw_semaphore cp_rwsem;		/* blocking FS operations */
 	struct rw_semaphore node_write;		/* locking node writes */
 	struct rw_semaphore node_change;	/* locking node change */
-	wait_queue_head_t cp_wait;
 	unsigned long last_time[MAX_TIME];	/* to store time in jiffies */
 	long interval_time[MAX_TIME];		/* to store thresholds */
 
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 83bf9a02f83f2..5f4d9abc079d6 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -3540,7 +3540,6 @@  static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 
 	init_rwsem(&sbi->cp_rwsem);
 	init_rwsem(&sbi->quota_sem);
-	init_waitqueue_head(&sbi->cp_wait);
 	init_sb_info(sbi);
 
 	err = init_percpu_info(sbi);