From patchwork Wed Nov 29 07:11:14 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Anand Jain X-Patchwork-Id: 10081505 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 1579560353 for ; Wed, 29 Nov 2017 07:11:00 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 0831B296B8 for ; Wed, 29 Nov 2017 07:11:00 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id F14BE296B7; Wed, 29 Nov 2017 07:10:59 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 766BF296B8 for ; Wed, 29 Nov 2017 07:10:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751478AbdK2HKz (ORCPT ); Wed, 29 Nov 2017 02:10:55 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:34675 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751165AbdK2HKy (ORCPT ); Wed, 29 Nov 2017 02:10:54 -0500 Received: from userv0022.oracle.com (userv0022.oracle.com [156.151.31.74]) by aserp1040.oracle.com (Sentrion-MTA-4.3.2/Sentrion-MTA-4.3.2) with ESMTP id vAT7ArA2018572 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Wed, 29 Nov 2017 07:10:53 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userv0022.oracle.com (8.14.4/8.14.4) with ESMTP id vAT7ArC1021970 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Wed, 29 Nov 2017 07:10:53 GMT Received: from abhmp0003.oracle.com (abhmp0003.oracle.com [141.146.116.9]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id vAT7Aq7a018884 for ; Wed, 29 Nov 2017 07:10:53 GMT Received: from tp.sg.oracle.com (/10.186.101.91) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 28 Nov 2017 23:10:52 -0800 From: Anand Jain To: linux-btrfs@vger.kernel.org Subject: [PATCH 1/2] btrfs: submit a normal bio for the mirror read Date: Wed, 29 Nov 2017 15:11:14 +0800 Message-Id: <20171129071115.7399-1-anand.jain@oracle.com> X-Mailer: git-send-email 2.15.0 X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP When the fist mirror failed to read we submit bio again to read from the 2nd mirror, however during this, we also set the flag REQ_FAILFAST_DEV which indicates to the underlying block device driver not to perform the default IO retry (sd, 5 counts), and thus command will be failed and returned at the first failed attempt. On the contrary, in fact, it should have been other way around that is, as 2nd mirror being the last copy of the data, it should rather try equally hard to make this read cmd successful and at the same time with or without REQ_FAILFAST_DEV there is no performance benefits if the command is successful in the first attempt itself. The only benefit which would be achieved with REQ_FAILFAST_DEV is that when both the copies encounter failed read, then for the applications, the EIO will be reported roughly 40% faster (since it saves 4 retries). But when first mirror has failed whats more important will be to make a successful read from the 2nd mirror. And for the DUP case where both the copies are on the same disk, this makes to retry 5 times on 2 different LBA/sector but on the same disk, which probably is not a good idea if your test case involves pulling out the disk. But as of now we don't have a way to tell the block layer how critical a read is, so that block layer can accommodate the retry dynamically. Signed-off-by: Anand Jain --- fs/btrfs/extent_io.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index d8eb457f2a70..29c03fb4d5af 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -2388,9 +2388,6 @@ static int bio_readpage_error(struct bio *failed_bio, u64 phy_offset, return -EIO; } - if (failed_bio->bi_vcnt > 1) - read_mode |= REQ_FAILFAST_DEV; - phy_offset >>= inode->i_sb->s_blocksize_bits; bio = btrfs_create_repair_bio(inode, failed_bio, failrec, page, start - page_offset(page),