Hi Nicholas and Claudio, > On Apr 5, 2022, at 4:54 PM, Song Liu <songliubraving@xxxxxx> wrote: > >> On Apr 5, 2022, at 12:07 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >> >> On Fri, Apr 01, 2022 at 10:22:00PM +0000, Song Liu wrote: >>>>> Please fix the underlying issues instead of papering over them and >>>>> creating a huge maintainance burden for others. >>> >>> After reading the code a little more, I wonder what would be best strategy. >>> IIUC, most of the kernel is not ready for huge page backed vmalloc memory. >>> For example, all the module_alloc cannot work with huge pages at the moment. >>> And the error Paul Menzel reported in drm_fb_helper.c will probably hit >>> powerpc with 5.17 kernel as-is? (trace attached below) >>> >>> Right now, we have VM_NO_HUGE_VMAP to let a user to opt out of huge pages. >>> However, given there are so many users of vmalloc, vzalloc, etc., we >>> probably do need a flag for the user to opt-in? >>> >>> Does this make sense? Any recommendations are really appreciated. >> >> I think there is multiple aspects here: >> >> - if we think that the kernel is not ready for hugepage backed vmalloc >> in general we need to disable it in powerpc for now. > > Nicholas and Claudio, > > What do you think about the status of hugepage backed vmalloc on powerpc? > I found module_alloc and kvm_s390_pv_alloc_vm() opt-out of huge pages. > But I am not aware of users that benefit from huge pages (except vfs hash, > which was mentioned in 8abddd968a30). Does an opt-in flag (instead of > current opt-out flag, VM_NO_HUGE_VMAP) make sense to you? Could you please share your comments on this? Specifically, does it make sense to replace VM_NO_HUGE_VMAP with an opt-in flag? If we think current opt-out flag is better approach, what would be the best practice to find all the cases to opt-out? Thanks, Song > Thanks, > Song > >> - if we think even in the longer run only some users can cope with >> hugepage backed vmalloc we need to turn it into an opt-in in >> general and not just for x86 >> - there still to appear various unresolved underlying x86 specific >> issues that need to be fixed either way >
