Messages in this thread | | | Date | Thu, 12 Mar 2020 18:45:35 -0700 | From | Jaegeuk Kim <> | Subject | Re: [PATCH] f2fs: fix long latency due to discard during umount |
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On 03/13, Sahitya Tummala wrote: > On Thu, Mar 12, 2020 at 10:02:42AM -0700, Jaegeuk Kim wrote: > > On 03/12, 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> > > > --- > > > fs/f2fs/segment.c | 14 +++++++++++++- > > > 1 file changed, 13 insertions(+), 1 deletion(-) > > > > > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c > > > index fb3e531..a06bbac 100644 > > > --- a/fs/f2fs/segment.c > > > +++ b/fs/f2fs/segment.c > > > @@ -1124,10 +1124,13 @@ 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; > > > > > > @@ -1203,6 +1206,11 @@ 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) && (dc->error == -EAGAIN)) { > > > + dc->state = D_PREP; > > > + err = dc->error; > > > + break; > > > + } > > > > > > atomic_inc(&dcc->issued_discard); > > > > > > @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi, > > > } > > > > > > __submit_discard_cmd(sbi, dpolicy, dc, &issued); > > > + if (dc->error == -EAGAIN) { > > > + congestion_wait(BLK_RW_ASYNC, HZ/50); > > > > --> need to be DEFAULT_IO_TIMEOUT > > Yes, i will update it. > > > > > > + __relocate_discard_cmd(dcc, dc); > > > > It seems we need to submit bio first, and then move dc to wait_list, if there's > > no error, in __submit_discard_cmd(). > > Yes, that is not changed and it still happens for the failed request > that is re-queued here too when it gets submitted again later. > > I am requeuing the discard request failed with -EAGAIN error back to > dcc->pend_list[] from wait_list. It will call submit_bio() for this request > and also move to wait_list when it calls __submit_discard_cmd() again next > time. Please let me know if I am missing anything?
This patch has no problem, but I'm thinking that __submit_discard_cmd() needs to return with any values by assumption where the waiting list should have submitted commands.
> > Thanks, > > > > > > + } > > > > > > if (issued >= dpolicy->max_requests) > > > break; > > > -- > > > 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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