On Fri, Aug 21, 2020 at 12:18:41PM -0700, Linus Torvalds wrote: > It also strikes me that I think the only architecture that uses the > whole arch_sync_kernel_mappings() thing is now just x86-32. > > [ Well, x86-64 still has it, but that's because we undid the 64-bit > removal, but it's on the verge of going away and x86-64 shouldn't > actually _need_ it any more ] > > So all of this seems to be purely for 32-bit x86. Which kind of makes > this all fail the smell test. Yeah, it is certainly not the nicest thing to have in generic mm code, but at least it is an improvement of the vmalloc_sync_all() interface we had before, where the function had to be called at random undefined places. And x86-32 needs it, as long as we have the !SHARED_KERNEL_PMD cases (which includes legacy paging). Or we also pre-allocate the PMDs on x86-32 and forbid large ioremap mappings. But since the vmalloc area gets larger with less RAM on x86-32, this would penalize low memory machines by using more pages for the pre-allocations. Not sure if making the vmalloc area on x86-32 a fixed 128MB range of address space independent of RAM size is doable or if it will break some machines. But with that pre-allocating PMDs would make more sense and we could get rid of the p?d_alloc_track() stuff. Regards, Joerg
