Messages in this thread | | | Date | Fri, 13 Mar 2020 09:09:12 +0530 | From | Sahitya Tummala <> | Subject | Re: [PATCH] f2fs: fix long latency due to discard during umount |
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On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote: > On 2020/3/12 19:14, 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)) { > > If we want to update dc->state, we need to cover it with dc->lock.
Sure, will update it.
> > > + dc->state = D_PREP; > > BTW, one dc can be referenced by multiple bios, so dc->state could be updated to > D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to > pending list... which is inconsistent status.
In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state will not be updated to D_DONE in f2fs_submit_discard_endio()?
Thanks,
> > Thanks, > > > + 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); > > + __relocate_discard_cmd(dcc, dc); > > + } > > > > if (issued >= dpolicy->max_requests) > > break; > >
-- -- 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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