On Tue 16-10-18 14:24:19, David Rientjes wrote: > On Tue, 16 Oct 2018, Michal Hocko wrote: > > > > I don't understand the point of extending smaps with yet another line. > > > > Because abusing a vma flag part is just wrong. What are you going to do > > when a next bug report states that the flag is set even though no > > userspace has set it and that leads to some malfunctioning? Can you rule > > that out? Even your abuse of the flag is surprising so why others > > wouldn't be? > > > > The flag has taken on the meaning of "thp disabled for this vma", how it > is set is not the scope of the flag. If a thp is explicitly disabled from > being eligible for thp, whether by madvise, prctl, or any future > mechanism, it should use VM_NOHUGEPAGE or show_smap_vma_flags() needs to > be modified. No, this is not the meaning which is documented nh - no-huge page advise flag and as far as I know it is only you who has complained so far. > > As I've said there are two things. Exporting PR_SET_THP_DISABLE to > > userspace so that a 3rd party process can query it. I've already > > explained why that might be useful. If you really insist on having > > a per-vma field then let's do it properly now. Are you going to agree on > > that? If yes, I am willing to spend my time on that but I am not going > > to bother if this will lead to "I want my vma field abuse anyway". > > I think what you and I want is largely irrelevant :) What's important is > that there are userspace implementations that query this today so > continuing to support it as the way to determine if a vma has been thp > disabled doesn't seem problematic and guarantees that userspace doesn't > break. Do you know of any other userspace except your usecase? Is there anything fundamental that would prevent a proper API adoption for you? -- Michal Hocko SUSE Labs
