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Date:   Thu, 9 Apr 2020 14:41:27 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ira Weiny <ira.weiny@intel.com>
Cc:     Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>,
        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
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Subject: Re: [PATCH V6 6/8] fs/xfs: Combine xfs_diflags_to_linux() and
 xfs_diflags_to_iflags()
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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.