From: Jaegeuk Kim <jaegeuk@kernel.org>
To: Sahitya Tummala <stummala@codeaurora.org>
Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount
Date: Thu, 12 Mar 2020 18:45:35 -0700 [thread overview]
Message-ID: <20200313014535.GA72547@google.com> (raw)
In-Reply-To: <20200313012604.GI20234@codeaurora.org>
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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next prev parent reply other threads:[~2020-03-13 1:45 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1584011671-20939-1-git-send-email-stummala@codeaurora.org>
2020-03-12 17:02 ` [f2fs-dev] [PATCH] f2fs: fix long latency due to discard during umount Jaegeuk Kim
[not found] ` <20200313012604.GI20234@codeaurora.org>
2020-03-13 1:45 ` Jaegeuk Kim [this message]
2020-03-13 5:12 ` Sahitya Tummala
2020-03-13 15:38 ` Jaegeuk Kim
2020-03-13 2:20 ` Chao Yu
[not found] ` <20200313033912.GJ20234@codeaurora.org>
2020-03-13 6:30 ` Chao Yu
[not found] ` <20200313110846.GL20234@codeaurora.org>
2020-03-16 0:52 ` Chao Yu
2020-03-16 3:52 ` Sahitya Tummala
[not found] <1584506689-5041-1-git-send-email-stummala@codeaurora.org>
2020-03-24 9:08 ` Chao Yu
2020-03-24 9:47 ` Chao Yu
2020-03-26 9:00 ` Chao Yu
2020-03-26 13:37 ` Sahitya Tummala
2020-03-27 1:51 ` Chao Yu
[not found] ` <20200327030542.GS20234@codeaurora.org>
2020-03-30 6:53 ` Sahitya Tummala
2020-03-30 8:38 ` Chao Yu
2020-03-30 10:16 ` Chao Yu
2020-03-30 10:51 ` Sahitya Tummala
2020-03-31 1:46 ` Chao Yu
2020-03-31 3:10 ` Sahitya Tummala
2020-03-31 3:50 ` Jaegeuk Kim
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