On 10/22/18 3:30 PM, Michal Hocko wrote: > On Mon 22-10-18 15:15:38, Vlastimil Babka wrote: >>> Forgot to add. One notable exception would be that the previous code >>> would allow to hit >>> WARN_ON_ONCE(policy->mode == MPOL_BIND && (gfp & __GFP_THISNODE)); >>> in policy_node if the requested node (e.g. cpu local one) was outside of >>> the mbind nodemask. This is not possible now. We haven't heard about any >>> such warning yet so it is unlikely that it happens though. >> >> I don't think the previous code could hit the warning, as the hugepage >> path that would add __GFP_THISNODE didn't call policy_node() (containing >> the warning) at all. IIRC early of your patch did hit the warning >> though, which is why you added the MPOL_BIND policy check. > > Are you sure? What prevents node_isset(node, policy_nodemask()) == F and > fallback to the !huge allocation path? That can indeed happen, but then the code also skipped the "gfp |= __GFP_THISNODE" part, right? So the warning wouldn't trigger. > alloc_pages_vma is usually called > with the local node and processes shouldn't run off their bounded num > mask but is that guaranteed? Moreover do_huge_pmd_wp_page_fallback uses > the former numa binding and that might be outside of the policy mask. > > In any case, as I've said this is highly unlikely to hit which is > underlined by the lack of reports. >
