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

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