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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 CE080ECDE5F for ; Tue, 24 Jul 2018 02:41:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 72CD620852 for ; Tue, 24 Jul 2018 02:41:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 72CD620852 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388413AbeGXDpY (ORCPT ); Mon, 23 Jul 2018 23:45:24 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:56696 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2388284AbeGXDpY (ORCPT ); Mon, 23 Jul 2018 23:45:24 -0400 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 1BAD84173CB18; Tue, 24 Jul 2018 10:41:11 +0800 (CST) Received: from [127.0.0.1] (10.134.22.195) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.382.0; Tue, 24 Jul 2018 10:40:26 +0800 Subject: Re: [PATCH v3] f2fs: issue discard align to section in LFS mode To: Yunlong Song , , , CC: , , , , , References: <1531836275-94933-1-git-send-email-yunlong.song@huawei.com> <1532005095-111878-1-git-send-email-yunlong.song@huawei.com> From: Chao Yu Message-ID: Date: Tue, 24 Jul 2018 10:40:27 +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: <1532005095-111878-1-git-send-email-yunlong.song@huawei.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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/7/19 20:58, Yunlong Song wrote: > For the case when sbi->segs_per_sec > 1 with lfs mode, take > section:segment = 5 for example, if the section prefree_map is > ...previous section | current section (1 1 0 1 1) | next section..., > then the start = x, end = x + 1, after start = start_segno + > sbi->segs_per_sec, start = x + 5, then it will skip x + 3 and x + 4, but > their bitmap is still set, which will cause duplicated > f2fs_issue_discard of this same section in the next write_checkpoint: > > round 1: section bitmap : 1 1 1 1 1, all valid, prefree_map: 0 0 0 0 0 > then rm data block NO.2, block NO.2 becomes invalid, prefree_map: 0 0 1 0 0 > write_checkpoint: section bitmap: 1 1 0 1 1, prefree_map: 0 0 0 0 0, > prefree of NO.2 is cleared, and no discard issued > > round 2: rm data block NO.0, NO.1, NO.3, NO.4 > all invalid, but prefree bit of NO.2 is set and cleared in round 1, then > prefree_map: 1 1 0 1 1 > write_checkpoint: section bitmap: 0 0 0 0 0, prefree_map: 0 0 0 1 1, no > valid blocks of this section, so discard issued, but this time prefree > bit of NO.3 and NO.4 is skipped due to start = start_segno + sbi->segs_per_sec; > > round 3: > write_checkpoint: section bitmap: 0 0 0 0 0, prefree_map: 0 0 0 1 1 -> > 0 0 0 0 0, no valid blocks of this section, so discard issued, > this time prefree bit of NO.3 and NO.4 is cleared, but the discard of > this section is sent again... > > To fix this problem, we can align the start and end value to section > boundary for fstrim and real-time discard operation, and decide to issue > discard only when the whole section is invalid, which can issue discard > aligned to section size as much as possible and avoid redundant discard. > > Signed-off-by: Yunlong Song > Signed-off-by: Chao Yu Reviewed-by: Chao Yu Thanks,