On 06/13/2018 05:13 AM, Michal Hocko wrote: > On Tue 12-06-18 10:11:33, Jason Baron wrote: > [...] >> Ok, I share the concern that there is a chance that userspace is relying >> on MADV_DONTNEED not free'ing locked memory. In that case, what if we >> introduce a MADV_DONTNEED_FORCE, which does everything that >> MADV_DONTNEED currently does but in addition will also free mlock areas. > > What about other types of vmas that are not allowed to MADV_DONTNEED? > _FORCE suggests that the user of the API know what he is doing so why > shouldn't we allow unmapping hugetlb pages or special PFNMAPS? Or do we > want to add MADV_DONTNEED_FORCE_FOR_REAL when somebody comes with > another usecase? > > I agree with Vlastimil that adding new madvise mode for niche case > sounds like a bad idea so we should better be sure that a new flag has > a reasonable semantic. Just allow mlocked pages is more of a tweak than > a proper semantic. So making it force for real requires to analyze what > that would mean for other vmas which are excluded now. > If its a new flag, I agree it makes sense to look at hugetlb and pfnmaps. pfnmaps might be more work, since it may require callbacks to do driver specific actions... I was able to do something very close to the original requirement of free'ing mlock'd pages, via using a tmpfs mmap that is mlock'd. And then using fallocate(FALLOC_FL_PUNCH_HOLE) to free the locked pages. I think the tmpfs is sufficient for my needs, I wonder if there is any other interest in this feature? Thanks, -Jason -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
