On 04/01, 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;

Can we use max queue depth of the block device?

>                 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.
> 
> -- 
> --
> 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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