From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chao Yu Subject: Re: [PATCH] f2fs: enlarge block plug coverage Date: Fri, 13 Apr 2018 15:13:55 +0800 Message-ID: References: <20180404085404.82184-1-yuchao0@huawei.com> <20180405035115.GC50337@jaegeuk-macbookpro.roam.corp.google.com> <03c21c2f-cb0e-dbd4-b48a-95c2678964d1@huawei.com> <20180409180241.GC17558@jaegeuk-macbookpro.roam.corp.google.com> <967b8819-da9a-b609-6a22-db8df5c7ec6c@huawei.com> <20180410041033.GE47598@jaegeuk-macbookpro.roam.corp.google.com> <20180413010615.GA53401@jaegeuk-macbookpro.roam.corp.google.com> <20180413040702.GC59368@jaegeuk-macbookpro.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180413040702.GC59368@jaegeuk-macbookpro.roam.corp.google.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Jaegeuk Kim Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, chao@kernel.org List-Id: linux-f2fs-devel.lists.sourceforge.net On 2018/4/13 12:07, Jaegeuk Kim wrote: > On 04/13, Chao Yu wrote: >> 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? ;) > > This is different one. Yup, if there will be no IO interference as you concerned before, can we accept it now? Thanks, > >> >> Thanks, >> >>> >>>> >>>> Thanks, >>>> >>>>> >>>>>> >>>>>> Thanks, >>>>>> >>>>>>> >>>>>>>> >>>>>>>> Thanks, >>>>>>>> >>>>>>>>> >>>>>>>>> Thanks, >>>>>>>>> >>>>>>>>>> >>>>>>>>>> Signed-off-by: Chao Yu >>>>>>>>>> --- >>>>>>>>>> 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 >>>>>>>>> >>>>>>>>> . >>>>>>>>> >>>>>>> >>>>>>> . >>>>>>> >>>>> >>>>> . >>>>> >>> >>> . >>> > > . >