Messages in this thread | | | Subject | Re: [PATCH] f2fs: enlarge block plug coverage | From | Chao Yu <> | Date | Tue, 10 Apr 2018 15:22:47 +0800 |
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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?
Thanks,
> >> >> Thanks, >> >>> >>>> >>>> Thanks, >>>> >>>>> >>>>> Thanks, >>>>> >>>>>> >>>>>> Signed-off-by: Chao Yu <yuchao0@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 >>>>> >>>>> . >>>>> >>> >>> . >>> > > . >
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