On June 2, 2017 11:55:12 PM GMT+03:00, Vlastimil Babka <vbabka@xxxxxxx> wrote: >On 06/02/2017 10:40 PM, Andrew Morton wrote: >> On Fri, 2 Jun 2017 22:31:47 +0200 Vlastimil Babka <vbabka@xxxxxxx> >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? Yes, we are going to use UFFDIO_COPY. We still might want to have control over THP in the future without changing per-VMA flags, though. -- Sincerely yours, Mike. -- 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
