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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 EAC5FC10DCE for ; Fri, 13 Mar 2020 06:31:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B9A942072F for ; Fri, 13 Mar 2020 06:31:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726328AbgCMGbv (ORCPT ); Fri, 13 Mar 2020 02:31:51 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:11670 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726001AbgCMGbv (ORCPT ); Fri, 13 Mar 2020 02:31:51 -0400 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 0ED352C1F36F6B23641E; Fri, 13 Mar 2020 14:31:01 +0800 (CST) Received: from [10.134.22.195] (10.134.22.195) by smtp.huawei.com (10.3.19.202) with Microsoft SMTP Server (TLS) id 14.3.487.0; Fri, 13 Mar 2020 14:30:56 +0800 Subject: Re: [PATCH] f2fs: fix long latency due to discard during umount To: Sahitya Tummala CC: Jaegeuk Kim , , References: <1584011671-20939-1-git-send-email-stummala@codeaurora.org> <20200313033912.GJ20234@codeaurora.org> From: Chao Yu Message-ID: Date: Fri, 13 Mar 2020 14:30:55 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20200313033912.GJ20234@codeaurora.org> 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/3/13 11:39, Sahitya Tummala wrote: > On Fri, Mar 13, 2020 at 10:20:04AM +0800, Chao Yu wrote: >> On 2020/3/12 19:14, Sahitya Tummala wrote: >>> F2FS already has a default timeout of 5 secs for discards that >>> can be issued during umount, but it can take more than the 5 sec >>> timeout if the underlying UFS device queue is already full and there >>> are no more available free tags to be used. In that case, submit_bio() >>> will wait for the already queued discard requests to complete to get >>> a free tag, which can potentially take way more than 5 sec. >>> >>> Fix this by submitting the discard requests with REQ_NOWAIT >>> flags during umount. This will return -EAGAIN for UFS queue/tag full >>> scenario without waiting in the context of submit_bio(). The FS can >>> then handle these requests by retrying again within the stipulated >>> discard timeout period to avoid long latencies. >>> >>> Signed-off-by: Sahitya Tummala >>> --- >>> fs/f2fs/segment.c | 14 +++++++++++++- >>> 1 file changed, 13 insertions(+), 1 deletion(-) >>> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >>> index fb3e531..a06bbac 100644 >>> --- a/fs/f2fs/segment.c >>> +++ b/fs/f2fs/segment.c >>> @@ -1124,10 +1124,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi, >>> struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info; >>> struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ? >>> &(dcc->fstrim_list) : &(dcc->wait_list); >>> - int flag = dpolicy->sync ? REQ_SYNC : 0; >>> + int flag; >>> block_t lstart, start, len, total_len; >>> int err = 0; >>> >>> + flag = dpolicy->sync ? REQ_SYNC : 0; >>> + flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0; >>> + >>> if (dc->state != D_PREP) >>> return 0; >>> >>> @@ -1203,6 +1206,11 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi, >>> bio->bi_end_io = f2fs_submit_discard_endio; >>> bio->bi_opf |= flag; >>> submit_bio(bio); >>> + if ((flag & REQ_NOWAIT) && (dc->error == -EAGAIN)) { >> >> If we want to update dc->state, we need to cover it with dc->lock. > > Sure, will update it. > >> >>> + dc->state = D_PREP; >> >> BTW, one dc can be referenced by multiple bios, so dc->state could be updated to >> D_DONE later by f2fs_submit_discard_endio(), however we just relocate it to >> pending list... which is inconsistent status. > > In that case dc->bio_ref will reflect it and until it becomes 0, the dc->state > will not be updated to D_DONE in f2fs_submit_discard_endio()? __submit_discard_cmd() lock() dc->state = D_SUBMIT; dc->bio_ref++; unlock() ... submit_bio() f2fs_submit_discard_endio() dc->error = -EAGAIN; lock() dc->bio_ref--; dc->state = D_PREP; dc->state = D_DONE; unlock() So finally, dc's state is D_DONE, and it's in wait list, then will be relocated to pending list. > > Thanks, > >> >> Thanks, >> >>> + err = dc->error; >>> + break; >>> + } >>> >>> atomic_inc(&dcc->issued_discard); >>> >>> @@ -1510,6 +1518,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi, >>> } >>> >>> __submit_discard_cmd(sbi, dpolicy, dc, &issued); >>> + if (dc->error == -EAGAIN) { >>> + congestion_wait(BLK_RW_ASYNC, HZ/50); >>> + __relocate_discard_cmd(dcc, dc); >>> + } >>> >>> if (issued >= dpolicy->max_requests) >>> break; >>> >