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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 55409C7EE24 for ; Tue, 6 Jun 2023 17:49:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238820AbjFFRs7 (ORCPT ); Tue, 6 Jun 2023 13:48:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48746 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238810AbjFFRsz (ORCPT ); Tue, 6 Jun 2023 13:48:55 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 013CF10F8 for ; Tue, 6 Jun 2023 10:48:54 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 9100C21990; Tue, 6 Jun 2023 17:48:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1686073733; h=from:from:reply-to:reply-to: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=34CF/je3QQ7ffTeHnBCUQ1OsQ9tAcOQKgWSSxxuTWVc=; b=0g63e9bkRYhXUEScOdCiqBtTUWG5xfsPCbLGOU+tQeYaGSaOy6F+kJ80rJ/SvtVtS8iM5/ eJci+UwAz74r23QZCZQCcjYGLo8TeH/6DsA2c08VIqF8BONMaSqcve1hK1IazDA7HZWNil g2cnhhGxtvKDQeQkxDrJDVY/TNcvry4= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1686073733; h=from:from:reply-to:reply-to: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=34CF/je3QQ7ffTeHnBCUQ1OsQ9tAcOQKgWSSxxuTWVc=; b=ZxgtRjcBplQjViD6/WeDt8Xd2pGPpMI1Y4cuSPGqzLaAn+D6WLfe91zvowf7HohQQBMzFL 2RZD8iw29xcrMNDw== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 6A2AD13776; Tue, 6 Jun 2023 17:48:53 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id uC0oGYVxf2TnZAAAMHmgww (envelope-from ); Tue, 06 Jun 2023 17:48:53 +0000 Date: Tue, 6 Jun 2023 19:42:38 +0200 From: David Sterba To: Chris Mason Cc: linux-btrfs@vger.kernel.org, dsterba@suse.com, josef@toxicpanda.com, boris@bur.io Subject: Re: [PATCH] btrfs: properly enable async discard when switching from RO->RW Message-ID: <20230606174238.GN25292@twin.jikos.cz> Reply-To: dsterba@suse.cz References: <20230605190315.2121377-1-clm@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230605190315.2121377-1-clm@fb.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Mon, Jun 05, 2023 at 12:03:15PM -0700, Chris Mason wrote: > async discard uses the BTRFS_FS_DISCARD_RUNNING bit in the fs_info to force > discards off when the filesystem has aborted or we're generally not able > to run discards. This gets flipped on when we're mounted rw, and also > when we go from ro->rw. > > Commit 63a7cb13071842 enabled async discard by default, and this meant > mount -o ro /dev/xxx /yyy had async discards turned on. > > Unfortunately, this meant our check in btrfs_remount_cleanup() would see > that discards are already on: > > /* If we toggled discard async */ > if (!btrfs_raw_test_opt(old_opts, DISCARD_ASYNC) && > btrfs_test_opt(fs_info, DISCARD_ASYNC)) > btrfs_discard_resume(fs_info); > > So, we'd never call btrfs_discard_resume() when remounting the root > filesystem from ro->rw. > > drgn shows this really nicely: > > import os > import sys > > from drgn.helpers.linux.fs import path_lookup > from drgn import NULL, Object, Type, cast > > def btrfs_sb(sb): > return cast("struct btrfs_fs_info *", sb.s_fs_info) > > if len(sys.argv) == 1: > path = "/" > else: > path = sys.argv[1] > > fs_info = cast("struct btrfs_fs_info *", path_lookup(prog, path).mnt.mnt_sb.s_fs_info) > > BTRFS_FS_DISCARD_RUNNING = 1 << prog['BTRFS_FS_DISCARD_RUNNING'] > if fs_info.flags & BTRFS_FS_DISCARD_RUNNING: > print("discard running flag is on") > else: > print("discard running flag is off") > > [root]# mount | grep nvme > /dev/nvme0n1p3 on / type btrfs > (rw,relatime,compress-force=zstd:3,ssd,discard=async,space_cache=v2,subvolid=5,subvol=/) > > [root]# ./discard_running.drgn > discard running flag is off > > [root]# mount -o remount,discard=sync / > [root]# mount -o remount,discard=async / > [root]# ./discard_running.drgn > discard running flag is on > > The fix used here is calling btrfs_discard_resume() when we're going > from ro->rw. It already checks to make sure the async discard flag is > on, so it'll do the right thing. > > Fixes: 63a7cb13071842 ("btrfs: auto enable discard=async when possible") > > Reviewed-by: Boris Burkov > Signed-off-by: Chris Mason Added to misc-next, thanks.