linux-kernel - Re: [RFC PATCH v2 14/14] dcache: Implement object migration

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Message-ID: <01000169e458534a-3c6a5d6f-3054-4c64-b5f9-7f46c811eeac-000000@email.amazonses.com>
Date:   Wed, 3 Apr 2019 17:56:27 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Al Viro <viro@...iv.linux.org.uk>
cc:     "Tobin C. Harding" <tobin@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Alexander Viro <viro@....linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Pekka Enberg <penberg@...helsinki.fi>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Andreas Dilger <adilger@...ger.ca>,
        Waiman Long <longman@...hat.com>,
        Tycho Andersen <tycho@...ho.ws>, Theodore Ts'o <tytso@....edu>,
        Andi Kleen <ak@...ux.intel.com>,
        David Chinner <david@...morbit.com>,
        Nick Piggin <npiggin@...il.com>,
        Rik van Riel <riel@...hat.com>,
        Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH v2 14/14] dcache: Implement object migration

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@...iv.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.