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Message-ID: <fd5b56ef-4f27-65b7-d3a2-71ef4425b452@huawei.com> Date: Fri, 13 Apr 2018 09:27:53 +0800 From: Chao Yu <yuchao0@...wei.com> To: Jaegeuk Kim <jaegeuk@...nel.org> CC: <linux-f2fs-devel@...ts.sourceforge.net>, <linux-kernel@...r.kernel.org>, <chao@...nel.org> Subject: Re: [PATCH] f2fs: enlarge block plug coverage 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 <yuchao0@...wei.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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