From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752137AbeDJHXG (ORCPT ); Tue, 10 Apr 2018 03:23:06 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:7165 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751794AbeDJHXE (ORCPT ); Tue, 10 Apr 2018 03:23:04 -0400 Subject: Re: [PATCH] f2fs: enlarge block plug coverage To: Jaegeuk Kim CC: , , 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> From: Chao Yu Message-ID: Date: Tue, 10 Apr 2018 15:22:47 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20180410041033.GE47598@jaegeuk-macbookpro.roam.corp.google.com> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.134.22.195] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >>>>>> --- >>>>>> 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 >>>>> >>>>> . >>>>> >>> >>> . >>> > > . >