netdev - Re: [PATCH 1/1] rosebush: Add new data structure

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Message-ID: <ZdrgV8GUE92HMojn@duke.home>
Date: Sun, 25 Feb 2024 01:38:15 -0500
From: Al Viro <viro@...nel.org>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: linux-kernel@...r.kernel.org, Thomas Graf <tgraf@...g.ch>,
	Herbert Xu <herbert@...dor.apana.org.au>, netdev@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, maple-tree@...ts.infradead.org,
	rcu@...r.kernel.org
Subject: Re: [PATCH 1/1] rosebush: Add new data structure

On Thu, Feb 22, 2024 at 08:37:24PM +0000, Matthew Wilcox (Oracle) wrote:
> Rosebush is a resizing hash table.  See
> Docuemntation/core-api/rosebush.rst for details.

Interesting...  A few obvious questions wrt dcache:
	* how do the locks that stuff nest wrt ->d_lock?  Inside?
	* same for rename_lock (on rename dentries change names/parents/hash
values).
	* we would be really forced to maintain DCACHE_UNHASHED in ->d_flags;
it's not impossible to do, but will take care (protection of ->d_flags has
several dark corners).
	* the cost of d_drop() goes up.  Might or might not get painful.
	* if the bucket locks nest inside ->d_lock, we'd better look out
for the latter getting held for longer.  Might get unpleasant.