Re: [RFC PATCH v2 7/8] Introduce dcache_is_aliasing() across all architectures

[Mathieu Desnoyers]

On 2024-01-30 21:48, Dave Chinner wrote:
> 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?

Good point, will do. I'm planning go rename as follows for v3 to
eliminate confusion with dentry cache (and with "page cache" in
general):

ARCH_HAS_CACHE_ALIASING -> ARCH_HAS_CPU_CACHE_ALIASING
dcache_is_aliasing() -> cpu_dcache_is_aliasing()

I noticed that you suggested "aliased" rather than "aliasing",
but I followed what arm64 did for icache_is_aliasing(). Do you
have a strong preference one way or another ?

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com