From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-20.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 03AB7C433E0 for ; Mon, 15 Mar 2021 10:31:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC4B064E64 for ; Mon, 15 Mar 2021 10:31:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229847AbhCOKbX (ORCPT ); Mon, 15 Mar 2021 06:31:23 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:13170 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229792AbhCOKbF (ORCPT ); Mon, 15 Mar 2021 06:31:05 -0400 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4DzXh95GkJzmXYg; Mon, 15 Mar 2021 18:28:41 +0800 (CST) Received: from [10.136.110.154] (10.136.110.154) by smtp.huawei.com (10.3.19.202) with Microsoft SMTP Server (TLS) id 14.3.498.0; Mon, 15 Mar 2021 18:31:00 +0800 Subject: Re: [PATCH] f2fs: fix the discard thread sleep timeout under high utilization To: Sahitya Tummala CC: Jaegeuk Kim , , References: <1615784186-2693-1-git-send-email-stummala@codeaurora.org> <49be0c70-4fe4-6acd-b508-08621f0623c0@huawei.com> <20210315074645.GA8562@codeaurora.org> <0c7220d7-416e-32b7-96cb-effd3f84d6e2@huawei.com> <20210315094502.GB8562@codeaurora.org> From: Chao Yu Message-ID: Date: Mon, 15 Mar 2021 18:31:00 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20210315094502.GB8562@codeaurora.org> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.136.110.154] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Sahitya, On 2021/3/15 17:45, Sahitya Tummala wrote: > Hi Chao, > > On Mon, Mar 15, 2021 at 04:10:22PM +0800, Chao Yu wrote: >> Hi Sahitya, >> >> On 2021/3/15 15:46, Sahitya Tummala wrote: >>> Hi Chao, >>> >>> On Mon, Mar 15, 2021 at 02:12:44PM +0800, Chao Yu wrote: >>>> Sahitya, >>>> >>>> On 2021/3/15 12:56, Sahitya Tummala wrote: >>>>> When f2fs is heavily utilized over 80%, the current discard policy >>>>> sets the max sleep timeout of discard thread as 50ms >>>>> (DEF_MIN_DISCARD_ISSUE_TIME). But this is set even when there are >>>>> no pending discard commands to be issued. This results into >>>>> unnecessary frequent and periodic wake ups of the discard thread. >>>>> This patch adds check for pending discard commands in addition >>>>> to heavy utilization condition to prevent those wake ups. >>>> >>>> Could this commit fix your issue? >>>> >>>> https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/commit/?h=dev&id=43f8c47ea7d59c7b2270835f1d7c4618a1ea27b6 >>>> >>> I don't think it will help because we are changing the max timeout of the >>> dpolicy itself in __init_discard_policy() when util > 80% as below - >>> >>> dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME; >>> >>> And issue_discard_thread() uses this value as wait_ms, when there >>> are no more pending discard commands to be issued. >>> >>> } else { >>> wait_ms = dpolicy.max_interval; >>> } >>> >>> >>> The new patch posted above is not changing anything related to the max_interval. >>> Hence, I think it won't help the uncessary wakeup problem I am trying to solve >>> for this condition - util > 80% and when there are no pending discards. >>> >>> Please let me know if i am missing something. >> >> Copied, thanks for the explanation. >> >> But there is another case which can cause this issue in the case of >> disk util < 80%. >> >> wait_ms = DEF_MIN_DISCARD_ISSUE_TIME; >> >> do { >> wait_event_interruptible_timeout(, wait_ms); >> >> ... >> >> if (!atomic_read(&dcc->discard_cmd_cnt)) >> [1] new statement >> continue; >> >> } while(); >> >> Then the loop will wakeup whenever 50ms timeout. >> > Yes, only for a short period of time i.e., until the first discard command > is issued. Once a discard is issued, it will use > wait_ms = dpolicy.max_interval; > >> So, to avoid this case, shouldn't we reset wait_ms to dpolicy.max_interval >> at [1]? >> > Yes, we can add that to cover the above case. > >> Meanwhile, how about relocating discard_cmd_cnt check after >> __init_discard_policy(DPOLICY_FORCE)? and olny set .max_interval to >> DEF_MAX_DISCARD_ISSUE_TIME if there is no discard command, and keep >> .granularity to 1? >> > > There is not need to change .granularity, right? It will be controlled I think so. > as per utilization as it is done today. Only max_interval and wait_ms > needs to be updated. Does this look good? > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c > index d7076796..958ad1e 100644 > --- a/fs/f2fs/segment.c > +++ b/fs/f2fs/segment.c > @@ -1772,13 +1772,16 @@ static int issue_discard_thread(void *data) > wait_ms = dpolicy.max_interval; > continue; > } > - if (!atomic_read(&dcc->discard_cmd_cnt)) > - continue; > - > if (sbi->gc_mode == GC_URGENT_HIGH || > !f2fs_available_free_memory(sbi, DISCARD_CACHE)) > __init_discard_policy(sbi, &dpolicy, DPOLICY_FORCE, 1); > > + if (!atomic_read(&dcc->discard_cmd_cnt)) { > + dpolicy.max_interval = DEF_MAX_DISCARD_ISSUE_TIME; > + wait_ms = dpolicy.max_interval; > + continue; > + } Hmm.. how about cleaning up to configure discard policy in __init_discard_policy()? Something like: --- fs/f2fs/segment.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c index 592927ccffa7..684463a70eb9 100644 --- a/fs/f2fs/segment.c +++ b/fs/f2fs/segment.c @@ -1118,7 +1118,9 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi, dpolicy->ordered = true; if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) { dpolicy->granularity = 1; - dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME; + if (atomic_read(&SM_I(sbi)->dcc_info->discard_cmd_cnt)) + dpolicy->max_interval = + DEF_MIN_DISCARD_ISSUE_TIME; } } else if (discard_type == DPOLICY_FORCE) { dpolicy->min_interval = DEF_MIN_DISCARD_ISSUE_TIME; @@ -1734,8 +1736,15 @@ static int issue_discard_thread(void *data) set_freezable(); do { - __init_discard_policy(sbi, &dpolicy, DPOLICY_BG, - dcc->discard_granularity); + if (sbi->gc_mode == GC_URGENT_HIGH || + !f2fs_available_free_memory(sbi, DISCARD_CACHE)) + __init_discard_policy(sbi, &dpolicy, DPOLICY_FORCE, 1); + else + __init_discard_policy(sbi, &dpolicy, DPOLICY_BG, + dcc->discard_granularity); + + if (!atomic_read(&dcc->discard_cmd_cnt)) + wait_ms = dpolicy.max_interval; wait_event_interruptible_timeout(*q, kthread_should_stop() || freezing(current) || @@ -1762,10 +1771,6 @@ static int issue_discard_thread(void *data) if (!atomic_read(&dcc->discard_cmd_cnt)) continue; - if (sbi->gc_mode == GC_URGENT_HIGH || - !f2fs_available_free_memory(sbi, DISCARD_CACHE)) - __init_discard_policy(sbi, &dpolicy, DPOLICY_FORCE, 1); - sb_start_intwrite(sbi->sb); issued = __issue_discard_cmd(sbi, &dpolicy); -- 2.29.2 Thoughts? Thanks, > + > sb_start_intwrite(sbi->sb); > > issued = __issue_discard_cmd(sbi, &dpolicy); > > thanks, > Sahitya. > >> Thanks, >> >>> >>> Thanks, >>> Sahitya. >>> >>>> Thanks, >>>> >>>>> >>>>> Signed-off-by: Sahitya Tummala >>>>> --- >>>>> fs/f2fs/segment.c | 5 ++++- >>>>> 1 file changed, 4 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >>>>> index dced46c..df30220 100644 >>>>> --- a/fs/f2fs/segment.c >>>>> +++ b/fs/f2fs/segment.c >>>>> @@ -1112,6 +1112,8 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi, >>>>> struct discard_policy *dpolicy, >>>>> int discard_type, unsigned int granularity) >>>>> { >>>>> + struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info; >>>>> + >>>>> /* common policy */ >>>>> dpolicy->type = discard_type; >>>>> dpolicy->sync = true; >>>>> @@ -1129,7 +1131,8 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi, >>>>> dpolicy->io_aware = true; >>>>> dpolicy->sync = false; >>>>> dpolicy->ordered = true; >>>>> - if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) { >>>>> + if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL && >>>>> + atomic_read(&dcc->discard_cmd_cnt)) { >>>>> dpolicy->granularity = 1; >>>>> dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME; >>>>> } >>>>> >>> >