On Fri 15-06-18 15:36:07, Jason Baron wrote: > > > On 06/13/2018 03:15 AM, Michal Hocko wrote: > > On Wed 13-06-18 08:32:19, Vlastimil Babka wrote: [...] > >> BTW I didn't get why we should allow this for MADV_DONTNEED but not > >> MADV_FREE. Can you expand on that? > > > > Well, I wanted to bring this up as well. I guess this would require some > > more hacks to handle the reclaim path correctly because we do rely on > > VM_LOCK at many places for the lazy mlock pages culling. > > > > The point of not allowing MADV_FREE on mlock'd pages for me was that > with mlock and even MLOCK_ON_FAULT, one can always can always determine > if a page is present or not (and thus avoid the major fault). Allowing > MADV_FREE on lock'd pages breaks that assumption. But once you have called MADV_FREE you cannot assume anything about the content until you touch the memory again. So you can safely assume a major fault for the worst case. Btw. why knowing whether you major fault is important in the first place? What is an application going to do about that information? -- Michal Hocko SUSE Labs
