From: Ira Weiny <ira.weiny@intel.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-kernel@vger.kernel.org,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Dan Williams <dan.j.williams@intel.com>,
Christoph Hellwig <hch@lst.de>,
"Theodore Y. Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
Jeff Moyer <jmoyer@redhat.com>,
linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH V6 6/8] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to_iflags()
Date: Wed, 8 Apr 2020 15:07:35 -0700 [thread overview]
Message-ID: <20200408220734.GA664132@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200408210236.GK24067@dread.disaster.area>
On Thu, Apr 09, 2020 at 07:02:36AM +1000, Dave Chinner wrote:
> On Wed, Apr 08, 2020 at 10:09:23AM -0700, Ira Weiny wrote:
[snip]
> >
> > 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.
<sigh> yes... you are correct.
But I don't like depending on the caller to clear the S_DAX flag if
xfs_inode_enable_dax() is false. IMO this function should clear the flag in
that case for consistency...
This is part of the reason I used the if/else logic from xfs_diflags_to_linux()
originally. It is very explicit.
>
> 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.
But this will not clear the S_DAX flag even if init is true. To me that is a
potential for confusion down the road.
>
> 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.
We already discussed evicting the inode and it was determined to be too
confusing.[*]
Furthermore, if we did want an interface like that why not allow the on-disk
flag to be set as well as cleared?
IMO, this function should set all of the flags consistently including S_DAX.
Ira
[*] https://lore.kernel.org/lkml/20200403072731.GA24176@lst.de/
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
next prev parent reply other threads:[~2020-04-08 22:07 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-07 18:29 [PATCH V6 0/8] Enable per-file/per-directory DAX operations V6 ira.weiny
2020-04-07 18:29 ` [PATCH V6 1/8] fs/xfs: Remove unnecessary initialization of i_rwsem ira.weiny
2020-04-07 23:46 ` Dave Chinner
2020-04-07 18:29 ` [PATCH V6 2/8] fs: Remove unneeded IS_DAX() check ira.weiny
2020-04-09 7:31 ` Christoph Hellwig
2020-04-09 14:57 ` Ira Weiny
2020-04-07 18:29 ` [PATCH V6 3/8] fs/stat: Define DAX statx attribute ira.weiny
2020-04-07 23:47 ` Dave Chinner
2020-04-07 18:29 ` [PATCH V6 4/8] fs/xfs: Make DAX mount option a tri-state ira.weiny
2020-04-07 23:59 ` Dave Chinner
2020-04-08 0:09 ` Ira Weiny
2020-04-08 0:48 ` Dave Chinner
2020-04-09 15:03 ` Ira Weiny
2020-04-07 18:29 ` [PATCH V6 5/8] fs/xfs: Create function xfs_inode_enable_dax() ira.weiny
2020-04-08 0:05 ` Dave Chinner
2020-04-08 0:13 ` Ira Weiny
2020-04-07 18:29 ` [PATCH V6 6/8] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to_iflags() ira.weiny
2020-04-08 2:08 ` Dave Chinner
2020-04-08 17:09 ` Ira Weiny
2020-04-08 21:02 ` Dave Chinner
2020-04-08 21:28 ` Dan Williams
2020-04-08 22:10 ` Ira Weiny
2020-04-08 23:58 ` Dave Chinner
2020-04-09 0:22 ` Ira Weiny
2020-04-09 12:41 ` Christoph Hellwig
2020-04-09 20:49 ` Ira Weiny
2020-04-08 22:07 ` Ira Weiny [this message]
2020-04-08 23:21 ` Dave Chinner
2020-04-09 0:12 ` Ira Weiny
2020-04-09 0:30 ` Darrick J. Wong
2020-04-09 15:29 ` Ira Weiny
2020-04-09 16:59 ` Darrick J. Wong
2020-04-09 17:17 ` Jan Kara
2020-04-09 20:54 ` Ira Weiny
2020-04-09 0:49 ` Dave Chinner
2020-04-09 12:40 ` Christoph Hellwig
2020-04-10 0:27 ` Dave Chinner
2020-04-07 18:29 ` [PATCH V6 7/8] fs/xfs: Change xfs_ioctl_setattr_dax_invalidate() to xfs_ioctl_dax_check() ira.weiny
2020-04-08 2:23 ` Dave Chinner
2020-04-08 9:58 ` Jan Kara
2020-04-08 21:09 ` Dave Chinner
2020-04-08 22:26 ` Ira Weiny
2020-04-08 23:48 ` Dave Chinner
2020-04-09 12:28 ` Christoph Hellwig
2020-04-08 15:37 ` Darrick J. Wong
2020-04-08 18:13 ` Ira Weiny
2020-04-16 5:39 ` [fs/xfs] 857c9841f8: xfstests.xfs.046.fail kernel test robot
2020-04-07 18:29 ` [PATCH V6 8/8] Documentation/dax: Update Usage section ira.weiny
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200408220734.GA664132@iweiny-DESK2.sc.intel.com \
--to=ira.weiny@intel.com \
--cc=dan.j.williams@intel.com \
--cc=darrick.wong@oracle.com \
--cc=david@fromorbit.com \
--cc=hch@lst.de \
--cc=jack@suse.cz \
--cc=jmoyer@redhat.com \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-xfs@vger.kernel.org \
--cc=tytso@mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).