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=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 CA08CC433E0 for ; Mon, 25 Jan 2021 18:16:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 93D4322583 for ; Mon, 25 Jan 2021 18:16:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731359AbhAYSPm (ORCPT ); Mon, 25 Jan 2021 13:15:42 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:37038 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731214AbhAYSPk (ORCPT ); Mon, 25 Jan 2021 13:15:40 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611598453; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=9aiOSMoFJWu8qbhYa3wTLZqRJl16rQM2+e9i9UHkfp8=; b=Ma+tGSrQppyBBQGaqXxaEiwPodn1PS4S/axf/1m+zkplr2oujkiL3/DmKPRxf8GnfwAHFO RYKyL8xXDQcXn/lPZykxQ20YssSkFyKpHJ97tNK+r/VY+24GiyeyDGVF7QuDIVsu8I/7sI DvkClw6hEM0lpnJDr/6k63GcyGt+P4s= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-204-W9yAwtJePEG0qiEeJe1i1Q-1; Mon, 25 Jan 2021 13:14:09 -0500 X-MC-Unique: W9yAwtJePEG0qiEeJe1i1Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8941F8144E0; Mon, 25 Jan 2021 18:14:08 +0000 (UTC) Received: from bfoster (ovpn-114-23.rdu2.redhat.com [10.10.114.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E06191981B; Mon, 25 Jan 2021 18:14:07 +0000 (UTC) Date: Mon, 25 Jan 2021 13:14:06 -0500 From: Brian Foster To: "Darrick J. Wong" Cc: Christoph Hellwig , linux-xfs@vger.kernel.org, hch@infradead.org, david@fromorbit.com Subject: Re: [PATCH 02/11] xfs: don't stall cowblocks scan if we can't take locks Message-ID: <20210125181406.GH2047559@bfoster> References: <161142791950.2171939.3320927557987463636.stgit@magnolia> <161142793080.2171939.11486862758521454210.stgit@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <161142793080.2171939.11486862758521454210.stgit@magnolia> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Sat, Jan 23, 2021 at 10:52:10AM -0800, Darrick J. Wong wrote: > From: Darrick J. Wong > > Don't stall the cowblocks scan on a locked inode if we possibly can. > We'd much rather the background scanner keep moving. > > Signed-off-by: Darrick J. Wong > Reviewed-by: Christoph Hellwig > --- > fs/xfs/xfs_icache.c | 21 ++++++++++++++++++--- > 1 file changed, 18 insertions(+), 3 deletions(-) > > > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > index c71eb15e3835..89f9e692fde7 100644 > --- a/fs/xfs/xfs_icache.c > +++ b/fs/xfs/xfs_icache.c > @@ -1605,17 +1605,31 @@ xfs_inode_free_cowblocks( > void *args) > { > struct xfs_eofblocks *eofb = args; > + bool wait; > int ret = 0; > > + wait = eofb && (eofb->eof_flags & XFS_EOF_FLAGS_SYNC); > + > if (!xfs_prep_free_cowblocks(ip)) > return 0; > > if (!xfs_inode_matches_eofb(ip, eofb)) > return 0; > > - /* Free the CoW blocks */ > - xfs_ilock(ip, XFS_IOLOCK_EXCL); > - xfs_ilock(ip, XFS_MMAPLOCK_EXCL); > + /* > + * If the caller is waiting, return -EAGAIN to keep the background > + * scanner moving and revisit the inode in a subsequent pass. > + */ > + if (!xfs_ilock_nowait(ip, XFS_IOLOCK_EXCL)) { > + if (wait) > + return -EAGAIN; > + return 0; > + } > + if (!xfs_ilock_nowait(ip, XFS_MMAPLOCK_EXCL)) { > + if (wait) > + ret = -EAGAIN; > + goto out_iolock; > + } Hmm.. I'd be a little concerned over this allowing a scan to repeat indefinitely with a competing workload because a restart doesn't carry over any state from the previous scan. I suppose the xfs_prep_free_cowblocks() checks make that slightly less likely on a given file, but I more wonder about a scenario with a large set of inodes in a particular AG with a sufficient amount of concurrent activity. All it takes is one trylock failure per scan to have to start the whole thing over again... hm? Brian > > /* > * Check again, nobody else should be able to dirty blocks or change > @@ -1625,6 +1639,7 @@ xfs_inode_free_cowblocks( > ret = xfs_reflink_cancel_cow_range(ip, 0, NULLFILEOFF, false); > > xfs_iunlock(ip, XFS_MMAPLOCK_EXCL); > +out_iolock: > xfs_iunlock(ip, XFS_IOLOCK_EXCL); > > return ret; >