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Date: Wed, 8 Apr 2020 14:30:24 +0530 From: Sahitya Tummala <stummala@...eaurora.org> To: Jaegeuk Kim <jaegeuk@...nel.org> Cc: Chao Yu <yuchao0@...wei.com>, linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org, stummala@...eaurora.org Subject: Re: [PATCH v3] f2fs: fix long latency due to discard during umount Hi Jaegeuk, On Fri, Apr 03, 2020 at 10:19:43AM -0700, Jaegeuk Kim wrote: > 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? I think it should be limited to 8 or 16 as Chao suggested, so that we can have better control on the given timeout value? Thoughts? Thanks, > > > 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@...eaurora.org> > > > > --- > > > > 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. -- -- 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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