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Date: Wed, 1 Apr 2020 14:52:01 +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 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;
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.
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