Messages in this thread Patch in this message | | | Date | Thu, 26 Mar 2020 19:07:00 +0530 | From | Sahitya Tummala <> | Subject | Re: [PATCH] f2fs: fix long latency due to discard during umount |
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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().
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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