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
>
> 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
> >>>>>
> >>>>> .
> >>>>>
> >>>
> >>> .
> >>>
> >
> > .
> >
