Re: [PATCH v5] arch/ia64: Restore arch-specific pgd_offset_k implementation

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On Thu, Aug 13, 2020 at 10:36:31PM +0100, Matthew Wilcox wrote:
> On Thu, Aug 13, 2020 at 11:55:21PM +0300, Mike Rapoport wrote:
> > +/*
> > + * In the kernel's mapped region we know everything is in region number 5, so
> > + * as an optimisation its PGD already points to the area for that region.
> 
> Is it actually an optimisation?  Are there any benchmarks where this
> makes any difference whatsoever?  Or should the comment be closer to
> 
> /* ia64 is gratuitously different.  Cope with it. */

It better suits arch/ia64/Kconfig ;-)

diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 5b4ec80bf586..205cdb91a6d5 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -62,6 +62,7 @@ config IA64
          the 32-bit X86 line.  The IA-64 Linux project has a home
          page at <http://www.linuxia64.org/> and a mailing list at
          <linux-ia64@xxxxxxxxxxxxxxx>.
+         IA-64 is gratuitously different. Cope with it.

> I might suggest that pgd be changed to be the same as every other pgd
> in the system, and every other architecture.
 
I did some grepping and got lost in IA-64 assembly, so I agree with
Jessica that it would open a can of worms.

-- 
Sincerely yours,
Mike.



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