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Date:   Thu, 9 Apr 2020 13:49:53 -0700
From:   Ira Weiny <ira.weiny@intel.com>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>,
        Dan Williams <dan.j.williams@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        "Theodore Y. Ts'o" <tytso@mit.edu>, 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()
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On Thu, Apr 09, 2020 at 02:41:27PM +0200, Christoph Hellwig wrote:
> On Wed, Apr 08, 2020 at 05:22:03PM -0700, Ira Weiny wrote:
> > > 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?
> 
> Sounds ok.  Note that we could also pretty trivially lift
> XFS_IDONTCACHE to the VFS if we need to apply the same scheme to
> ext4.

Yes I have been slowing working on ext4 in the background.  So lifting
XXX_IDONTCACHE to VFS will be part of that series.

Thanks,
Ira