Re: [PATCH v3] f2fs: fix long latency due to discard during umount

From: Jaegeuk Kim
Date: Fri Apr 03 2020 - 13:19:46 EST

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 <stummala@xxxxxxxxxxxxxx>
> > > ---
> > > 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.