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Date: Tue, 31 Mar 2020 11:46:55 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Sahitya Tummala <stummala@...eaurora.org>
Cc: Chao Yu <yuchao0@...wei.com>,
linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] f2fs: fix long latency due to discard during umount
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()?
>
> 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.
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