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SubjectRe: [PATCH] f2fs: fix long latency due to discard during umount
On Fri, Mar 27, 2020 at 09:51:43AM +0800, Chao Yu wrote:
> On 2020/3/26 21:37, Sahitya Tummala wrote:
> > Hi Chao,
> >
> > On Thu, Mar 26, 2020 at 05:00:18PM +0800, Chao Yu wrote:
> >> Hi Sahitya,
> >>
> >> On 2020/3/18 12:44, 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.
> >>>
> >>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> >>> ---
> >>> v2:
> >>> - Handle the case where a dc can have multiple bios associated with it
> >>>
> >>> fs/f2fs/f2fs.h | 1 +
> >>> fs/f2fs/segment.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++-------
> >>> 2 files changed, 74 insertions(+), 10 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>> index 12a197e..67b8dcc 100644
> >>> --- a/fs/f2fs/f2fs.h
> >>> +++ b/fs/f2fs/f2fs.h
> >>> @@ -340,6 +340,7 @@ struct discard_cmd_control {
> >>> struct list_head pend_list[MAX_PLIST_NUM];/* store pending entries */
> >>> struct list_head wait_list; /* store on-flushing entries */
> >>> struct list_head fstrim_list; /* in-flight discard from fstrim */
> >>> + struct list_head retry_list; /* list of cmds to retry */
> >>> wait_queue_head_t discard_wait_queue; /* waiting queue for wake-up */
> >>> unsigned int discard_wake; /* to wake up discard thread */
> >>> struct mutex cmd_lock;
> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>> index fb3e531..4162c76 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;
> >>> - block_t lstart, start, len, total_len;
> >>> + int flag;
> >>> + block_t lstart, start, len, total_len, orig_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;
> >>>
> >>> @@ -1139,7 +1145,7 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>> lstart = dc->lstart;
> >>> start = dc->start;
> >>> len = dc->len;
> >>> - total_len = len;
> >>> + orig_len = total_len = len;
> >>>
> >>> dc->len = 0;
> >>>
> >>> @@ -1203,6 +1209,14 @@ 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) {
> >>> + dc->len = orig_len;
> >>> + list_move(&dc->list, &dcc->retry_list);
> >>> + err = dc->error;
> >>
> >> I encounter lots of dmesg, which should be printed by __remove_discard_cmd()
> >>
> >> F2FS-fs (dm-0): Issue discard(23552, 23552, 2) failed, ret: -11
> >>
> >> This should happen only if we didn't handle all discard in 5 seconds during
> >> umount.
> >>
> >> So I doubt we failed to move dc to retry_list, because after submit_bio(),
> >> end_io() is not called synchronously as the bio was just pluged?
> >>
> > This can happen if a discard cmd has multiple bios and at least 1 bio is
> > already submitted and when submitting other bios, we encounter -EAGAIN.
> > In this case, this dc will be moved to retry_list and will be moved back
> > to dcc->pend_list only if the dc->bio_ref becomes 0 within 5 sec timeout.
> > If it doesn't become zero, then it will be left in retry_list itself, which
> > will be later removed from retry_list. Before removing from retry_list we
> > will however ensure that submitted bio is done i.e., dc->bio_ref is 0, but
> > dc->error will be -EAGAIN as this dc could not be requeued/retried.
> >
> > So this is expected, where it only means that this dc could not be
> > submitted/retried again within timeout. I think we can ignore
> > this -EAGAIN error in __remove_discard_cmd().
>
> With this patch, most of xfstest cases cost 5 * n second longer than before.
>
> E.g. generic/003, during umount(), we looped into retrying one bio
> submission.
>
> [61279.829724] F2FS-fs (zram1): Found nat_bits in checkpoint
> [61279.885337] F2FS-fs (zram1): Mounted with checkpoint version = 5cf3cb8e
> [61281.912832] submit discard bio start [23555,1]
> [61281.912835] f2fs_submit_discard_endio [23555,1] err:-11
> [61281.912836] submit discard bio end [23555,1]
> [61281.912836] move dc to retry list [23555,1]
>
> ...
>
> [61286.881212] submit discard bio start [23555,1]
> [61286.881217] f2fs_submit_discard_endio [23555,1] err:-11
> [61286.881223] submit discard bio end [23555,1]
> [61286.881224] move dc to retry list [23555,1]
> [61286.905198] submit discard bio start [23555,1]
> [61286.905203] f2fs_submit_discard_endio [23555,1] err:-11
> [61286.905205] submit discard bio end [23555,1]
> [61286.905206] move dc to retry list [23555,1]
> [61286.929157] F2FS-fs (zram1): Issue discard(23555, 23555, 1) failed, ret: -11
>
> Could you take a look at this issue?

Let me check and get back on this.

Thanks,

>
> Thanks,
>
> >
> > Thanks,
> >
> >> Thanks,
> >>
> >>> + break;
> >>> + }
> >>> + }
> >>>
> >>> atomic_inc(&dcc->issued_discard);
> >>>
> >>> @@ -1463,6 +1477,40 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
> >>> return issued;
> >>> }
> >>>
> >>> +static bool __should_discard_retry(struct f2fs_sb_info *sbi,
> > s> > + struct discard_policy *dpolicy)
> >>> +{
> >>> + struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>> + struct discard_cmd *dc, *tmp;
> >>> + bool retry = false;
> >>> + unsigned long flags;
> >>> +
> >>> + if (dpolicy->type != DPOLICY_UMOUNT)
> >>> + f2fs_bug_on(sbi, 1);
> >>> +
> >>> + mutex_lock(&dcc->cmd_lock);
> >>> + list_for_each_entry_safe(dc, tmp, &(dcc->retry_list), list) {
> >>> + if (dpolicy->timeout != 0 &&
> >>> + f2fs_time_over(sbi, dpolicy->timeout)) {
> >>> + retry = false;
> >>> + break;
> >>> + }
> >>> +
> >>> + spin_lock_irqsave(&dc->lock, flags);
> >>> + if (!dc->bio_ref) {
> >>> + dc->state = D_PREP;
> >>> + dc->error = 0;
> >>> + reinit_completion(&dc->wait);
> >>> + __relocate_discard_cmd(dcc, dc);
> >>> + retry = true;
> >>> + }
> >>> + spin_unlock_irqrestore(&dc->lock, flags);
> >>> + }
> >>> + mutex_unlock(&dcc->cmd_lock);
> >>> +
> >>> + return retry;
> >>> +}
> >>> +
> >>> static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>> struct discard_policy *dpolicy)
> >>> {
> >>> @@ -1470,12 +1518,13 @@ 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;
> >>>
> >>> if (dpolicy->timeout != 0)
> >>> f2fs_update_time(sbi, dpolicy->timeout);
> >>>
> >>> +retry:
> >>> for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
> >>> if (dpolicy->timeout != 0 &&
> >>> f2fs_time_over(sbi, dpolicy->timeout))
> >>> @@ -1509,7 +1558,10 @@ 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);
> >>>
> >>> if (issued >= dpolicy->max_requests)
> >>> break;
> >>> @@ -1522,6 +1574,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>> break;
> >>> }
> >>>
> >>> + if (!list_empty(&dcc->retry_list) &&
> >>> + __should_discard_retry(sbi, dpolicy))
> >>> + goto retry;
> >>> +
> >>> if (!issued && io_interrupted)
> >>> issued = -1;
> >>>
> >>> @@ -1613,6 +1669,12 @@ static unsigned int __wait_discard_cmd_range(struct f2fs_sb_info *sbi,
> >>> goto next;
> >>> }
> >>>
> >>> + if (dpolicy->type == DPOLICY_UMOUNT &&
> >>> + !list_empty(&dcc->retry_list)) {
> >>> + wait_list = &dcc->retry_list;
> >>> + goto next;
> >>> + }
> >>> +
> >>> return trimmed;
> >>> }
> >>>
> >>> @@ -2051,6 +2113,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
> >>> for (i = 0; i < MAX_PLIST_NUM; i++)
> >>> INIT_LIST_HEAD(&dcc->pend_list[i]);
> >>> INIT_LIST_HEAD(&dcc->wait_list);
> >>> + INIT_LIST_HEAD(&dcc->retry_list);
> >>> INIT_LIST_HEAD(&dcc->fstrim_list);
> >>> mutex_init(&dcc->cmd_lock);
> >>> atomic_set(&dcc->issued_discard, 0);
> >>>
> >

--
--
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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