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=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 73FC7C433E0 for ; Tue, 4 Aug 2020 03:00:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7FD4220738 for ; Tue, 4 Aug 2020 03:00:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727806AbgHDDAJ (ORCPT ); Mon, 3 Aug 2020 23:00:09 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:9324 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725840AbgHDDAI (ORCPT ); Mon, 3 Aug 2020 23:00:08 -0400 Received: from DGGEMS404-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 2119C2BC0355340BEDBF; Tue, 4 Aug 2020 11:00:06 +0800 (CST) Received: from [10.164.122.247] (10.164.122.247) by smtp.huawei.com (10.3.19.204) with Microsoft SMTP Server (TLS) id 14.3.487.0; Tue, 4 Aug 2020 11:00:01 +0800 Subject: Re: [f2fs-dev] [PATCH] f2fs: remove a waiter for checkpoint completion To: Jaegeuk Kim CC: , , , Eric Biggers References: <20200803172825.4077289-1-jaegeuk@kernel.org> <9638d2c5-cfd0-359f-187a-8e23bc6d822d@huawei.com> <20200804010412.GA866340@google.com> <98ac9355-bb6c-5109-da73-4ab7cdbbf8d5@huawei.com> <20200804024317.GA884736@google.com> From: Chao Yu Message-ID: <6d84bfea-13a3-af84-16ad-5d0c7eedeb67@huawei.com> Date: Tue, 4 Aug 2020 11:00:01 +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: <20200804024317.GA884736@google.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.164.122.247] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/8/4 10:43, Jaegeuk Kim wrote: > On 08/04, Chao Yu wrote: >> On 2020/8/4 9:04, Jaegeuk Kim wrote: >>> On 08/04, Chao Yu wrote: >>>> On 2020/8/4 1:28, Jaegeuk Kim wrote: >>>>> It doesn't need to wait for checkpoint being completed triggered by end_io. >>>>> >>>>> [ 20.157753] ------------[ cut here ]------------ >>>>> [ 20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430 >>>>> [ 20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0 >>>>> ... >>>>> [ 20.176110] __submit_merged_write_cond+0x191/0x310 >>>>> [ 20.176739] f2fs_submit_merged_write+0x18/0x20 >>>>> [ 20.177323] f2fs_wait_on_all_pages+0x269/0x2d0 >>>>> [ 20.177899] ? block_operations+0x980/0x980 >>>>> [ 20.178441] ? __kasan_check_read+0x11/0x20 >>>>> [ 20.178975] ? finish_wait+0x260/0x260 >>>>> [ 20.179488] ? percpu_counter_set+0x147/0x230 >>>>> [ 20.180049] do_checkpoint+0x1757/0x2a50 >>>>> [ 20.180558] f2fs_write_checkpoint+0x840/0xaf0 >>>>> [ 20.181126] f2fs_sync_fs+0x287/0x4a0 >>>>> >>>>> Reported-by: Eric Biggers >>>>> Signed-off-by: Jaegeuk Kim >>>>> --- >>>>> fs/f2fs/checkpoint.c | 6 +----- >>>>> fs/f2fs/data.c | 4 ---- >>>>> fs/f2fs/f2fs.h | 1 - >>>>> fs/f2fs/super.c | 1 - >>>>> 4 files changed, 1 insertion(+), 11 deletions(-) >>>>> >>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c >>>>> index 99c8061da55b9..2bdddc725e677 100644 >>>>> --- a/fs/f2fs/checkpoint.c >>>>> +++ b/fs/f2fs/checkpoint.c >>>>> @@ -1255,11 +1255,7 @@ static void unblock_operations(struct f2fs_sb_info *sbi) >>>>> void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type) >>>>> { >>>>> - DEFINE_WAIT(wait); >>>>> - >>>>> for (;;) { >>>>> - prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE); >>>> >>>> Wouldn't that case high cpu usage before io end? >>> >>> This is a critical path to wait for IO completion in checkpoint, which would be >>> better to wait for it to avoid long latency to continue filesystem operations. >> >> Yup, in previous implementation, last end_io wakes up checkpoint() waiter, we >> didn't waste any time there. >> >>> Moreover, I expect io_schedule_timeout() can mitigate such the CPU overhead and >>> actually we don't need to make there-in context switches as well. >> >> Then io_schedule_timeout() in this loop may give CPU time slice to other thread >> until scheduler reselect checkpoint(), that would cause longer latency? > > Hmm, how about this then? > >>>From 4956afa1cedc019cabf6e8bff7bc48d3bcf7a3f5 Mon Sep 17 00:00:00 2001 > From: Jaegeuk Kim > Date: Mon, 3 Aug 2020 19:37:12 -0700 > Subject: [PATCH] f2fs: prepare a waiter before entering io_schedule > > This is to avoid sleep() in the waiter thread. > > [ 20.157753] ------------[ cut here ]------------ > [ 20.158393] do not call blocking ops when !TASK_RUNNING; state=2 set at [<0000000096354225>] prepare_to_wait+0xcd/0x430 > [ 20.159858] WARNING: CPU: 1 PID: 1152 at kernel/sched/core.c:7142 __might_sleep+0x149/0x1a0 > ... > [ 20.176110] __submit_merged_write_cond+0x191/0x310 > [ 20.176739] f2fs_submit_merged_write+0x18/0x20 > [ 20.177323] f2fs_wait_on_all_pages+0x269/0x2d0 > [ 20.177899] ? block_operations+0x980/0x980 > [ 20.178441] ? __kasan_check_read+0x11/0x20 > [ 20.178975] ? finish_wait+0x260/0x260 > [ 20.179488] ? percpu_counter_set+0x147/0x230 > [ 20.180049] do_checkpoint+0x1757/0x2a50 > [ 20.180558] f2fs_write_checkpoint+0x840/0xaf0 > [ 20.181126] f2fs_sync_fs+0x287/0x4a0 > > Reported-by: Eric Biggers > Signed-off-by: Jaegeuk Kim Better, Reviewed-by: Chao Yu Thanks, > --- > fs/f2fs/checkpoint.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c > index 99c8061da55b9..ff807e14c8911 100644 > --- a/fs/f2fs/checkpoint.c > +++ b/fs/f2fs/checkpoint.c > @@ -1258,8 +1258,6 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type) > DEFINE_WAIT(wait); > > for (;;) { > - prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE); > - > if (!get_pages(sbi, type)) > break; > > @@ -1271,6 +1269,8 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type) > FS_CP_META_IO); > else if (type == F2FS_WB_CP_DATA) > f2fs_submit_merged_write(sbi, DATA); > + > + prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE); > io_schedule_timeout(DEFAULT_IO_TIMEOUT); > } > finish_wait(&sbi->cp_wait, &wait); >