Messages in this thread | | | Subject | Re: [PATCH] f2fs: fix long latency due to discard during umount | From | Chao Yu <> | Date | Fri, 27 Mar 2020 09:51:43 +0800 |
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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?
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); >>> >
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