Messages in this thread | | | Date | Fri, 27 Mar 2020 08:35:42 +0530 | From | Sahitya Tummala <> | Subject | Re: [PATCH] f2fs: fix long latency due to discard during umount |
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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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