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

Joel Fernandes joel at joelfernandes.org
Wed Oct 24 19:21:19 PDT 2018


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?

thanks,

 - Joel




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