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From: Ira Weiny <ira.weiny@intel.com>
To: Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>,
	Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"Darrick J. Wong" <darrick.wong@oracle.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 <linux-ext4@vger.kernel.org>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	linux-fsdevel <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 17:22:03 -0700	[thread overview]
Message-ID: <20200409002203.GE664132@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200408235836.GQ24067@dread.disaster.area>

On Thu, Apr 09, 2020 at 09:58:36AM +1000, Dave Chinner wrote:
> On Wed, Apr 08, 2020 at 02:28:30PM -0700, Dan Williams wrote:
> > On Wed, Apr 8, 2020 at 2:02 PM Dave Chinner <david@fromorbit.com> wrote:
> > > 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.
> 
> You mean something like XFS_IDONTCACHE?
> 
> i.e. the functionality already exists in XFS to selectively evict an
> inode from cache when the last reference to it is dropped rather
> than let it go to the LRUs and hang around in memory.
> 
> That flag can be set when changing the on disk DAX flag, and we can
> tweak how it works so new cache hits don't clear it (as happens
> now). Hence the only thing that can prevent eviction are active
> references.
> 
> That means we'll still need to stop the application and drop_caches,
> because we need to close all the files and purge the dentries that
> hold references to the inode before it can be evicted.

That sounds like a great idea...

Jan?  Christoph?

I will reiterate though that any delayed S_DAX change be done as a follow on
series to the one proposed here.

Ira

  reply	other threads:[~2020-04-09  0:22 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 [this message]
2020-04-09 12:41               ` Christoph Hellwig
2020-04-09 20:49                 ` Ira Weiny
2020-04-08 22:07         ` Ira Weiny
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

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