On 2020/4/1 17:22, Sahitya Tummala wrote:
> Hi Jaegeuk,
> 
> On Tue, Mar 31, 2020 at 11:46:55AM -0700, Jaegeuk Kim wrote:
>> On 03/30, 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.
>>
>> Sorry, Sahitya, but, do we really need to do like this? How about just
>> controlling # of outstanding discarding bios in __issue_discard_cmd()?
> 
> Do you mean something like this?
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 1a62b27..860dd43 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1099,7 +1099,7 @@ static void __init_discard_policy(struct f2fs_sb_info 
> *sbi,
>         } else if (discard_type == DPOLICY_FSTRIM) {
>                 dpolicy->io_aware = false;
>         } else if (discard_type == DPOLICY_UMOUNT) {
> -               dpolicy->max_requests = UINT_MAX;
> +               dpolicy->max_requests = 30;

8 or 16?

It looks more simple than previous implementation.

Thanks,


>                 dpolicy->io_aware = false;
>                 /* we need to issue all to keep CP_TRIMMED_FLAG */
>                 dpolicy->granularity = 1;
> @@ -1470,12 +1470,14 @@ 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, issued;
>         bool io_interrupted = false;
> 
>         if (dpolicy->timeout != 0)
>                 f2fs_update_time(sbi, dpolicy->timeout);
> 
> +retry:
> +       issued = 0;
>         for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
>                 if (dpolicy->timeout != 0 &&
>                                 f2fs_time_over(sbi, dpolicy->timeout))
> @@ -1522,6 +1524,11 @@ static int __issue_discard_cmd(struct f2fs_sb_info 
> *sbi,
>                         break;
>         }
> 
> +       if (dpolicy->type == DPOLICY_UMOUNT && issued) {
> +               __wait_all_discard_cmd(sbi, dpolicy);
> +               goto retry;
> +       }
> +
>         if (!issued && io_interrupted)
>                 issued = -1;
> 
> Thanks,
> 
>>
>>>
>>> Signed-off-by: Sahitya Tummala <stumm...@codeaurora.org>
>>> ---
>>> v3:
>>> -Handle the regression reported by Chao with v2.
>>> -simplify the logic to split the dc with multiple bios incase any bio 
>>> returns
>>>  EAGAIN and retry those new dc within 5 sec timeout.
>>>
>>>  fs/f2fs/segment.c | 65 
>>> +++++++++++++++++++++++++++++++++++++++++++------------
>>>  1 file changed, 51 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index fb3e531..55d18c7 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;
>>> +   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;
>>>  
>>> @@ -1192,10 +1198,6 @@ static int __submit_discard_cmd(struct f2fs_sb_info 
>>> *sbi,
>>>             dc->bio_ref++;
>>>             spin_unlock_irqrestore(&dc->lock, flags);
>>>  
>>> -           atomic_inc(&dcc->queued_discard);
>>> -           dc->queued++;
>>> -           list_move_tail(&dc->list, wait_list);
>>> -
>>>             /* sanity check on discard range */
>>>             __check_sit_bitmap(sbi, lstart, lstart + len);
>>>  
>>> @@ -1203,6 +1205,29 @@ 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) {
>>> +                           spin_lock_irqsave(&dc->lock, flags);
>>> +                           dc->len -= len;
>>> +                           if (!dc->len) {
>>> +                                   dc->len = total_len;
>>> +                                   dc->state = D_PREP;
>>> +                                   reinit_completion(&dc->wait);
>>> +                           } else {
>>> +                                   dcc->undiscard_blks -= total_len;
>>> +                                   if (dc->state == D_PARTIAL)
>>> +                                           dc->state = D_SUBMIT;
>>> +                           }
>>> +                           err = dc->error;
>>> +                           dc->error = 0;
>>> +                           spin_unlock_irqrestore(&dc->lock, flags);
>>> +                           break;
>>> +                   }
>>> +           }
>>> +
>>> +           atomic_inc(&dcc->queued_discard);
>>> +           dc->queued++;
>>> +           list_move_tail(&dc->list, wait_list);
>>>  
>>>             atomic_inc(&dcc->issued_discard);
>>>  
>>> @@ -1214,8 +1239,9 @@ static int __submit_discard_cmd(struct f2fs_sb_info 
>>> *sbi,
>>>             len = total_len;
>>>     }
>>>  
>>> -   if (!err && len)
>>> -           __update_discard_tree_range(sbi, bdev, lstart, start, len);
>>> +   if ((!err || err == -EAGAIN) && total_len && dc->start != start)
>>> +           __update_discard_tree_range(sbi, bdev, lstart, start,
>>> +                                   total_len);
>>>     return err;
>>>  }
>>>  
>>> @@ -1470,12 +1496,15 @@ 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;
>>> +   bool retry;
>>>  
>>>     if (dpolicy->timeout != 0)
>>>             f2fs_update_time(sbi, dpolicy->timeout);
>>>  
>>> +retry:
>>> +   retry = false;
>>>     for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
>>>             if (dpolicy->timeout != 0 &&
>>>                             f2fs_time_over(sbi, dpolicy->timeout))
>>> @@ -1509,7 +1538,12 @@ 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);
>>> +                           retry = true;
>>> +                   }
>>>  
>>>                     if (issued >= dpolicy->max_requests)
>>>                             break;
>>> @@ -1522,6 +1556,9 @@ static int __issue_discard_cmd(struct f2fs_sb_info 
>>> *sbi,
>>>                     break;
>>>     }
>>>  
>>> +   if (retry)
>>> +           goto retry;
>>> +
>>>     if (!issued && io_interrupted)
>>>             issued = -1;
>>>  
>>> -- 
>>> 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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