On 2018/4/13 9:06, Jaegeuk Kim wrote:
> On 04/10, Chao Yu wrote:
>> On 2018/4/10 12:10, Jaegeuk Kim wrote:
>>> On 04/10, Chao Yu wrote:
>>>> On 2018/4/10 2:02, Jaegeuk Kim wrote:
>>>>> On 04/08, Chao Yu wrote:
>>>>>> On 2018/4/5 11:51, Jaegeuk Kim wrote:
>>>>>>> On 04/04, Chao Yu wrote:
>>>>>>>> This patch enlarges block plug coverage in __issue_discard_cmd, in
>>>>>>>> order to collect more pending bios before issuing them, to avoid
>>>>>>>> being disturbed by previous discard I/O in IO aware discard mode.
>>>>>>>
>>>>>>> Hmm, then we need to wait for huge discard IO for over 10 secs, which
>>>>>>
>>>>>> We found that total discard latency is rely on total discard number we
>>>>>> issued
>>>>>> last time instead of range or length discard covered. IMO, if we don't
>>>>>> change
>>>>>> .max_requests value, we will not suffer longer latency.
>>>>>>
>>>>>>> will affect following read/write IOs accordingly. In order to avoid
>>>>>>> that,
>>>>>>> we actually need to limit the discard size.
>>>>
>>>> Do you mean limit discard count or discard length?
>>>
>>> Both of them.
>>>
>>>>
>>>>>>
>>>>>> If you are worry about I/O interference in between discard and rw, I
>>>>>> suggest to
>>>>>> decrease .max_requests value.
>>>>>
>>>>> What do you mean? This will produce more pending requests in the queue?
>>>>
>>>> I mean after applying this patch, we can queue more discard IOs in plug
>>>> inside
>>>> task, otherwise, previous issued discard in block layer can make is_idle()
>>>> be false,
>>>> then it can stop IO awared user to issue pending discard command.
>>>
>>> Then, unplug will issue lots of discard commands, which affects the
>>> following rw
>>> latencies. My preference would be issuing discard commands one by one as
>>> much as
>>> possible.
>>
>> Hmm.. for you concern, we can turn down IO priority of discard from
>> background?
>
> That makes much more sense to me. :P
Then, this patch which enlarge plug coverage will not still a problem, right? ;)
Thanks,
>
>>
>> Thanks,
>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>>>
>>>>>>>> Signed-off-by: Chao Yu <yuch...@huawei.com>
>>>>>>>> ---
>>>>>>>> fs/f2fs/segment.c | 7 +++++--
>>>>>>>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>>>>>> index 8f0b5ba46315..4287e208c040 100644
>>>>>>>> --- a/fs/f2fs/segment.c
>>>>>>>> +++ b/fs/f2fs/segment.c
>>>>>>>> @@ -1208,10 +1208,12 @@ static int __issue_discard_cmd(struct
>>>>>>>> f2fs_sb_info *sbi,
>>>>>>>> pend_list = &dcc->pend_list[i];
>>>>>>>>
>>>>>>>> mutex_lock(&dcc->cmd_lock);
>>>>>>>> +
>>>>>>>> + blk_start_plug(&plug);
>>>>>>>> +
>>>>>>>> if (list_empty(pend_list))
>>>>>>>> goto next;
>>>>>>>> f2fs_bug_on(sbi, !__check_rb_tree_consistence(sbi,
>>>>>>>> &dcc->root));
>>>>>>>> - blk_start_plug(&plug);
>>>>>>>> list_for_each_entry_safe(dc, tmp, pend_list, list) {
>>>>>>>> f2fs_bug_on(sbi, dc->state != D_PREP);
>>>>>>>>
>>>>>>>> @@ -1227,8 +1229,9 @@ static int __issue_discard_cmd(struct
>>>>>>>> f2fs_sb_info *sbi,
>>>>>>>> if (++iter >= dpolicy->max_requests)
>>>>>>>> break;
>>>>>>>> }
>>>>>>>> - blk_finish_plug(&plug);
>>>>>>>> next:
>>>>>>>> + blk_finish_plug(&plug);
>>>>>>>> +
>>>>>>>> mutex_unlock(&dcc->cmd_lock);
>>>>>>>>
>>>>>>>> if (iter >= dpolicy->max_requests)
>>>>>>>> --
>>>>>>>> 2.15.0.55.gc2ece9dc4de6
>>>>>>>
>>>>>>> .
>>>>>>>
>>>>>
>>>>> .
>>>>>
>>>
>>> .
>>>
>
> .
>
