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SubjectRe: [f2fs-dev] [PATCH] f2fs: remove a waiter for checkpoint completion
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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);
>>>
> .
>

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