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Date:   Wed, 3 Apr 2019 17:56:27 +0000
From:   Christopher Lameter <cl@linux.com>
To:     Al Viro <viro@zeniv.linux.org.uk>
cc:     "Tobin C. Harding" <tobin@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>,
        Alexander Viro <viro@ftp.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        Pekka Enberg <penberg@cs.helsinki.fi>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Matthew Wilcox <willy@infradead.org>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Andreas Dilger <adilger@dilger.ca>,
        Waiman Long <longman@redhat.com>,
        Tycho Andersen <tycho@tycho.ws>, Theodore Ts'o <tytso@mit.edu>,
        Andi Kleen <ak@linux.intel.com>,
        David Chinner <david@fromorbit.com>,
        Nick Piggin <npiggin@gmail.com>,
        Rik van Riel <riel@redhat.com>,
        Hugh Dickins <hughd@google.com>, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC PATCH v2 14/14] dcache: Implement object migration
In-Reply-To: <20190403170811.GR2217@ZenIV.linux.org.uk>
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References: <20190403042127.18755-1-tobin@kernel.org> <20190403042127.18755-15-tobin@kernel.org> <20190403170811.GR2217@ZenIV.linux.org.uk>
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On Wed, 3 Apr 2019, Al Viro wrote:

> Let's do d_invalidate() on random dentries and hope they go away.
> With convoluted and brittle logics for deciding which ones to
> spare, which is actually wrong.  This will pick mountpoints
> and tear them out, to start with.
>
> NAKed-by: Al Viro <viro@zeniv.linux.org.uk>
>
> And this is a NAK for the entire approach; if it has a positive refcount,
> LEAVE IT ALONE.  Period.  Don't play this kind of games, they are wrong.
> d_invalidate() is not something that can be done to an arbitrary dentry.

Well could you help us figure out how to do it the right way? We (the MM
guys) are having a hard time not being familiar with the filesystem stuff.

This is an RFC and we want to know how to do this right.