On Thu, Aug 17, 2017 at 3:02 PM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: > On Thu, Aug 17, 2017 at 02:59:20PM -0700, Dan Williams wrote: >> On Thu, Aug 17, 2017 at 2:55 PM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: >> > On Thu, Aug 17, 2017 at 02:39:16PM -0700, Andrew Morton wrote: >> >> On Wed, 16 Aug 2017 20:05:29 -0400 J__r__me Glisse <jglisse@xxxxxxxxxx> wrote: >> >> >> >> > Heterogeneous Memory Management (HMM) (description and justification) >> >> >> >> The patchset adds 55 kbytes to x86_64's mm/*.o and there doesn't appear >> >> to be any way of avoiding this overhead, or of avoiding whatever >> >> runtime overheads are added. >> > >> > HMM have already been integrated in couple of Red Hat kernel and AFAIK there >> > is no runtime performance issue reported. Thought the RHEL version does not >> > use static key as Dan asked. >> > >> >> >> >> It also adds 18k to arm's mm/*.o and arm doesn't support HMM at all. >> >> >> >> So that's all quite a lot of bloat for systems which get no benefit from >> >> the patchset. What can we do to improve this situation (a lot)? >> > >> > I will look into why object file grow so much on arm. My guess is that the >> > new migrate code is the bulk of that. I can hide the new page migration code >> > behind a kernel configuration flag. >> >> Shouldn't we completely disable all of it unless there is a driver in >> the kernel that selects it? > > At one point people asked to be able to use the new migrate helper without > HMM and hence why it is not behind any HMM kconfig. > > IIRC even ARM folks were interested pretty much all SOC have several DMA > engine that site idle and i think people where toying with the idea of using > this new helper to make use of them. But i can add a different kconfig to > hide this code and if people want to use it they will have to select it. If they were interested then I would expect their use case would be included in this patchset so the infrastructure and at least one consumer can land together. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
