linux-kernel - Re: [PATCH V6 6/8] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to

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Date:   Thu, 9 Apr 2020 14:41:27 +0200
From:   Christoph Hellwig <hch@....de>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH V6 6/8] fs/xfs: Combine xfs_diflags_to_linux() and
 xfs_diflags_to_iflags()

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.