On Sat, 23 Dec 2017, [email protected] wrote:
> Hi folks,
>
> as I understand, a reason to have page coloring is extra broken MIPS
> hardware which has cache aliasing issues unless a large page size
> is used. picking the same color avoids aliasing.
Could be to work around cache aliasing, or it could be used to reduce
cache line contention. I'd say it's mostly used for the latter. This is
an optimization, not functional enforcement.
> now, looking at uvm_pagealloc_pgfl:
>
> do {
> /* trying to find pages in color.. */
> /* goto success */
>
> color = (color + 1) & uvmexp.colormask;
> } while (color != trycolor);
>
> which means that if we fail to find a page in the requested color, we'll
> try another color. I think this might end up inducing cache aliasing
> issues, and we should instead fail for this case.
>
> thoughts?
If there are functional issues with page mappings they should be handled
in the pmap layer, either failing the map request, or disabling any
potentially aliased caches.
Eduardo
