On 06/02/2017 10:40 PM, Andrew Morton wrote: > On Fri, 2 Jun 2017 22:31:47 +0200 Vlastimil Babka <vba...@suse.cz> wrote: >>> Perhaps we should be adding new prctl modes to select this new >>> behaviour and leave the existing PR_SET_THP_DISABLE behaviour as-is? >> >> I think we can reasonably assume that most users of the prctl do just >> the fork() & exec() thing, so they will be unaffected. > > That sounds optimistic. Perhaps people are using the current behaviour > to set on particular mapping to MMF_DISABLE_THP, with > > prctl(PR_SET_THP_DISABLE) > mmap() > prctl(PR_CLR_THP_DISABLE) > > ? > > Seems a reasonable thing to do.
Using madvise(MADV_NOHUGEPAGE) seems reasonabler to me, with the same effect. And it's older (2.6.38). > But who knows - people do all sorts of > inventive things. Yeah :( but we can hope they don't even know that the prctl currently behaves they way it does - man page doesn't suggest it would, and most of us in this thread found it surprising. >> And as usual, if >> somebody does complain in the end, we revert and try the other way? > > But by then it's too late - the new behaviour will be out in the field. Revert in stable then? But I don't think this patch should go to stable. I understand right that CRIU will switch to the UFFDIO_COPY approach and doesn't need the prctl change/new madvise anymore?
