[PATCH 1/4] treewide: remove unused address argument from pte_alloc functions (v2)

Peter Zijlstra peterz at infradead.org
Fri Oct 26 01:52:02 PDT 2018


On Wed, Oct 24, 2018 at 07:21:19PM -0700, Joel Fernandes wrote:
> On Wed, Oct 24, 2018 at 10:37:16AM +0200, Peter Zijlstra wrote:
> > On Fri, Oct 12, 2018 at 06:31:57PM -0700, Joel Fernandes (Google) wrote:
> > > This series speeds up mremap(2) syscall by copying page tables at the
> > > PMD level even for non-THP systems. There is concern that the extra
> > > 'address' argument that mremap passes to pte_alloc may do something
> > > subtle architecture related in the future that may make the scheme not
> > > work.  Also we find that there is no point in passing the 'address' to
> > > pte_alloc since its unused. So this patch therefore removes this
> > > argument tree-wide resulting in a nice negative diff as well. Also
> > > ensuring along the way that the enabled architectures do not do anything
> > > funky with 'address' argument that goes unnoticed by the optimization.
> > 
> > Did you happen to look at the history of where that address argument
> > came from? -- just being curious here. ISTR something vague about
> > architectures having different paging structure for different memory
> > ranges.
> 
> I didn't happen to do that analysis but from code analysis, no architecutre
> is using it. Since its unused in the kernel, may be such architectures don't
> exist or were removed, so we don't need to bother? Could you share more about
> your concern with the removal of this argument?

No concerns at all with removing it; I was purely curious as to the
origin of the unused argument. Kirill provided that answer.




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