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=-3.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 A9695C2BA1B for ; Wed, 8 Apr 2020 21:28:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 684FE2075E for ; Wed, 8 Apr 2020 21:28:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="pI/Ke2eb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730123AbgDHV2q (ORCPT ); Wed, 8 Apr 2020 17:28:46 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:37652 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729692AbgDHV2p (ORCPT ); Wed, 8 Apr 2020 17:28:45 -0400 Received: by mail-ed1-f65.google.com with SMTP id de14so10638210edb.4 for ; Wed, 08 Apr 2020 14:28:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=gsc90LPV5vuebvWSwowSniEuuhSDnHS3fNotzCrMHhI=; b=pI/Ke2eb3jkjDRXlYPpj3VkVyEJR335iPpo7DsBKOj3g+DjMNeZJvrbuvyfq267OUD 4I7dyDJsclQ5Slr540XjTRPHixi7zmEpnJbFNdrNPHGDhdR50DfloDptknHgyMIdpzbg +WLguh/vuRJiMIUGJsbXd21ZCz0w3EwbKD2oPW2TCb/WITmelq+YNrw74a1YeDapL9IM 0UVEJDV/xqFxic1LVguPMWHIax948Z3G5lH3pCNHB7nyS8N+6MiW7SNMEuDx41bQqr/o XwWla1TJ1Cpdx1w3dRFYLcVNTKUZee16zXqvVoociuElI8kaSzpd8d2REh/aJHXedYW1 1U7Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=gsc90LPV5vuebvWSwowSniEuuhSDnHS3fNotzCrMHhI=; b=jeQfBgVuSxYnXofg7ND+Tbmqbau+oCcqPCiwKV0jHsliZDL7hLnSFYEhDep9pHkRgl Pqc/ezCUCBKZuIJK9GXzXg+zx2xigVtR1bMOa0yDGwVvrN/l7o09JqFIF9E1vRbzEnJa ydRvVAxpNeHamzA6wDN5OI4Xf6J07pNZdLJS3XZSggd82w4ZwSAeyglGsAvCJqSXPpZ8 spuxPGUnamw746ThejqW8UAPHedU0Ej0uer3nRAz+A22roQ9QhDy/uKzeARlafVnt/I7 QodtMr8k/FSXgHYYum47DhfTZoXztj+o4GwMASpGiO3s2XfYToqIoDgo161rKIwKjSPR bKTQ== X-Gm-Message-State: AGi0Pub1d8VCG6xhcWI4KPWvzINGzeH89nZefhrtZV2cdAfr7PzYycS0 GHqhQ4ec5Is0UbLkCNZrhNaV0RH7hTS/tI8yHwCMwg== X-Google-Smtp-Source: APiQypJk5ijyBzx01h6/nF0/FztOREeQcwbT2SBq1CK12n6G3N8IiyFCzIyOVWUiYtoBKEH4Kr8GDj8vGyt7ncuxacA= X-Received: by 2002:a17:907:1185:: with SMTP id uz5mr4432200ejb.335.1586381321924; Wed, 08 Apr 2020 14:28:41 -0700 (PDT) MIME-Version: 1.0 References: <20200407182958.568475-1-ira.weiny@intel.com> <20200407182958.568475-7-ira.weiny@intel.com> <20200408020827.GI24067@dread.disaster.area> <20200408170923.GC569068@iweiny-DESK2.sc.intel.com> <20200408210236.GK24067@dread.disaster.area> In-Reply-To: <20200408210236.GK24067@dread.disaster.area> From: Dan Williams Date: Wed, 8 Apr 2020 14:28:30 -0700 Message-ID: Subject: Re: [PATCH V6 6/8] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to_iflags() To: Dave Chinner Cc: Ira Weiny , Linux Kernel Mailing List , "Darrick J. Wong" , Christoph Hellwig , "Theodore Y. Ts'o" , Jan Kara , Jeff Moyer , linux-ext4 , linux-xfs , linux-fsdevel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 8, 2020 at 2:02 PM Dave Chinner wrote: > > On Wed, Apr 08, 2020 at 10:09:23AM -0700, Ira Weiny wrote: > > On Wed, Apr 08, 2020 at 12:08:27PM +1000, Dave Chinner wrote: > > > On Tue, Apr 07, 2020 at 11:29:56AM -0700, ira.weiny@intel.com wrote: > > > > From: Ira Weiny > > > > [snip] > > > > > > > > > > -STATIC void > > > > -xfs_diflags_to_linux( > > > > - struct xfs_inode *ip) > > > > -{ > > > > - struct inode *inode = VFS_I(ip); > > > > - unsigned int xflags = xfs_ip2xflags(ip); > > > > - > > > > - if (xflags & FS_XFLAG_IMMUTABLE) > > > > - inode->i_flags |= S_IMMUTABLE; > > > > - else > > > > - inode->i_flags &= ~S_IMMUTABLE; > > > > - if (xflags & FS_XFLAG_APPEND) > > > > - inode->i_flags |= S_APPEND; > > > > - else > > > > - inode->i_flags &= ~S_APPEND; > > > > - if (xflags & FS_XFLAG_SYNC) > > > > - inode->i_flags |= S_SYNC; > > > > - else > > > > - inode->i_flags &= ~S_SYNC; > > > > - if (xflags & FS_XFLAG_NOATIME) > > > > - inode->i_flags |= S_NOATIME; > > > > - else > > > > - inode->i_flags &= ~S_NOATIME; > > > > -#if 0 /* disabled until the flag switching races are sorted out */ > > > > - if (xflags & FS_XFLAG_DAX) > > > > - inode->i_flags |= S_DAX; > > > > - else > > > > - inode->i_flags &= ~S_DAX; > > > > -#endif > > > > > > So this variant will set the flag in the inode if the disk inode > > > flag is set, otherwise it will clear it. It does it with if/else > > > branches. > > > > > > > > > > diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c > > > > index e07f7b641226..a4ac8568c8c7 100644 > > > > --- a/fs/xfs/xfs_iops.c > > > > +++ b/fs/xfs/xfs_iops.c > > > > @@ -1259,7 +1259,7 @@ xfs_inode_supports_dax( > > > > return xfs_inode_buftarg(ip)->bt_daxdev != NULL; > > > > } > > > > > > > > -STATIC bool > > > > +static bool > > > > xfs_inode_enable_dax( > > > > struct xfs_inode *ip) > > > > { > > > > > > This belongs in the previous patch. > > > > Ah yea... Sorry. > > > > Fixed in V7 > > > > > > > > > @@ -1272,26 +1272,38 @@ xfs_inode_enable_dax( > > > > return false; > > > > } > > > > > > > > -STATIC void > > > > +void > > > > xfs_diflags_to_iflags( > > > > - struct inode *inode, > > > > - struct xfs_inode *ip) > > > > + struct xfs_inode *ip, > > > > + bool init) > > > > { > > > > - uint16_t flags = ip->i_d.di_flags; > > > > - > > > > - inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC | > > > > - S_NOATIME | S_DAX); > > > > > > And this code cleared all the flags in the inode first, then > > > set them if the disk inode flag is set. This does not require > > > branches, resulting in more readable code and better code > > > generation. > > > > > > > + struct inode *inode = VFS_I(ip); > > > > + uint diflags = xfs_ip2xflags(ip); > > > > > > > > - if (flags & XFS_DIFLAG_IMMUTABLE) > > > > + if (diflags & FS_XFLAG_IMMUTABLE) > > > > inode->i_flags |= S_IMMUTABLE; > > > > - if (flags & XFS_DIFLAG_APPEND) > > > > + else > > > > + inode->i_flags &= ~S_IMMUTABLE; > > > > > > > + if (diflags & FS_XFLAG_APPEND) > > > > inode->i_flags |= S_APPEND; > > > > - if (flags & XFS_DIFLAG_SYNC) > > > > + else > > > > + inode->i_flags &= ~S_APPEND; > > > > + if (diflags & FS_XFLAG_SYNC) > > > > inode->i_flags |= S_SYNC; > > > > - if (flags & XFS_DIFLAG_NOATIME) > > > > + else > > > > + inode->i_flags &= ~S_SYNC; > > > > + if (diflags & FS_XFLAG_NOATIME) > > > > inode->i_flags |= S_NOATIME; > > > > - if (xfs_inode_enable_dax(ip)) > > > > - inode->i_flags |= S_DAX; > > > > + else > > > > + inode->i_flags &= ~S_NOATIME; > > > > + > > > > + /* Only toggle the dax flag when initializing */ > > > > + if (init) { > > > > + if (xfs_inode_enable_dax(ip)) > > > > + inode->i_flags |= S_DAX; > > > > + else > > > > + inode->i_flags &= ~S_DAX; > > > > + } > > > > } > > > > > > IOWs, this: > > > > > > struct inode *inode = VFS_I(ip); > > > unsigned int xflags = xfs_ip2xflags(ip); > > > unsigned int flags = 0; > > > > > > if (xflags & FS_XFLAG_IMMUTABLE) > > > flags |= S_IMMUTABLE; > > > if (xflags & FS_XFLAG_APPEND) > > > flags |= S_APPEND; > > > if (xflags & FS_XFLAG_SYNC) > > > flags |= S_SYNC; > > > if (xflags & FS_XFLAG_NOATIME) > > > flags |= S_NOATIME; > > > if ((xflags & FS_XFLAG_DAX) && init) > > > flags |= S_DAX; > > > > > > inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC | S_NOATIME); > > > inode->i_flags |= flags; > > > > > > ends up being much easier to read and results in better code > > > generation. And we don't need to clear the S_DAX flag when "init" is > > > set, because we are starting from an inode that has no flags set > > > (because init!)... > > > > This sounds good but I think we need a slight modification to make the function equivalent in functionality. > > > > void > > xfs_diflags_to_iflags( > > struct xfs_inode *ip, > > bool init) > > { > > struct inode *inode = VFS_I(ip); > > unsigned int xflags = xfs_ip2xflags(ip); > > unsigned int flags = 0; > > > > inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC | S_NOATIME | > > S_DAX); > > We don't want to clear the dax flag here, ever, if it is already > set. That is an externally visible change and opens us up (again) to > races where IS_DAX() changes half way through a fault path. IOWs, avoiding > clearing the DAX flag was something I did explicitly in the above > code fragment. > > And it makes the logic clearer by pre-calculating the new flags, > then clearing and setting the inode flags together, rather than > having the spearated at the top and bottom of the function. > > THis leads to an obvious conclusion: if we never clear the in memory > S_DAX flag, we can actually clear the on-disk flag safely, so that > next time the inode cycles into memory it won't be using DAX. IOWs, > admins can stop the applications, clear the DAX flag and drop > caches. This should result in the inode being recycled and when the > app is restarted it will run without DAX. No ned for deleting files, > copying large data sets, etc just to turn off an inode flag. Makes sense, but is that sufficient? I recall you saying there might be a multitude of other reasons that the inode is not evicted, not the least of which is races [1]. Does this need another flag, lets call it "dax toggle" to track the "I requested the inode to clear the flag, but on cache-flush + restart the inode never got evicted" case. S_DAX almost plays this role, but it loses the ability to audit which files are pending an inode eviction event. So the dax-toggle flag indicates to the kernel to xor the toggle value with the inode flag on inode instantiation and the dax inode flag is never directly manipulated by the ioctl path. [1]: http://lore.kernel.org/r/20191025003603.GE4614@dread.disaster.area