From: Chao Yu <yuchao0@huawei.com>
To: Sahitya Tummala <stummala@codeaurora.org>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>,
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: Fri, 13 Mar 2020 14:30:55 +0800 [thread overview]
Message-ID: <a8f01157-0b1b-d83a-488d-bb48cf8954ab@huawei.com> (raw)
In-Reply-To: <20200313033912.GJ20234@codeaurora.org>
On 2020/3/13 11:39, Sahitya Tummala wrote:
> 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()?
__submit_discard_cmd()
lock()
dc->state = D_SUBMIT;
dc->bio_ref++;
unlock()
...
submit_bio()
f2fs_submit_discard_endio()
dc->error = -EAGAIN;
lock()
dc->bio_ref--;
dc->state = D_PREP;
dc->state = D_DONE;
unlock()
So finally, dc's state is D_DONE, and it's in wait list, then will be relocated
to pending list.
>
> 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;
>>>
>
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next prev parent reply other threads:[~2020-03-13 6:31 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
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 [this message]
[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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