linux-kernel - Re: [RFC PATCH v2 7/8] Introduce dcache_is

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Message-ID: <Zbm1CLy+YZWx2IuO@dread.disaster.area>
Date: Wed, 31 Jan 2024 13:48:40 +1100
From: Dave Chinner <david@...morbit.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Dan Williams <dan.j.williams@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
	Arnd Bergmann <arnd@...db.de>, Russell King <linux@...linux.org.uk>,
	linux-cxl@...r.kernel.org, nvdimm@...ts.linux.dev,
	linux-xfs@...r.kernel.org
Subject: Re: [RFC PATCH v2 7/8] Introduce dcache_is_aliasing() across all
 architectures

On Tue, Jan 30, 2024 at 11:52:54AM -0500, Mathieu Desnoyers wrote:
> Introduce a generic way to query whether the dcache is virtually aliased
> on all architectures. Its purpose is to ensure that subsystems which
> are incompatible with virtually aliased data caches (e.g. FS_DAX) can
> reliably query this.
> 
> For dcache aliasing, there are three scenarios dependending on the
> architecture. Here is a breakdown based on my understanding:
> 
> A) The dcache is always aliasing:
> 
> * arc
> * csky
> * m68k (note: shared memory mappings are incoherent ? SHMLBA is missing there.)
> * sh
> * parisc

/me wonders why the dentry cache aliasing has problems on these
systems.

Oh, dcache != fs/dcache.c (the VFS dentry cache).

Can you please rename this function appropriately so us dumb
filesystem people don't confuse cpu data cache configurations with
the VFS dentry cache aliasing when we read this code? Something like
cpu_dcache_is_aliased(), perhaps?

-Dave.
-- 
Dave Chinner
david@...morbit.com