Re: [PATCH] mm: numa: Do not trap faults on shared data section pages.

[Christopher Lameter]

On Tue, 16 Jan 2018, Mel Gorman wrote:

> My main source of discomfort is the fact that this is permanent as two
> processes perfectly isolated but with a suitably shared COW mapping
> will never migrate the data. A potential improvement to get the reported
> bandwidth up in the test program would be to skip the rest of the VMA if
> page_mapcount != 1 in a COW mapping as it would be reasonable to assume
> the remaining pages in the VMA are also affected and the scan is wasteful.
> There are counter-examples to this but I suspect that the full VMA being
> shared is the common case. Whether you do that or not;

Same concern here. Typically CAP_SYS_NICE will bypass the check that the
page is only mapped to a single process and the check looks exactly like
the ones for manual migration. Using CAP_SYS_NICE would be surprising
here since autonuma is not triggered by the currently running process.

Can we configure this somehow via sysfs?