On Thu, Mar 21, 2019 at 07:59:35PM +0000, Thomas Hellstrom wrote: > On Thu, 2019-03-21 at 09:52 -0400, Jerome Glisse wrote: > > On Thu, Mar 21, 2019 at 01:22:35PM +0000, Thomas Hellstrom wrote: > > > This is basically apply_to_page_range with added functionality: > > > Allocating missing parts of the page table becomes optional, which > > > means that the function can be guaranteed not to error if > > > allocation > > > is disabled. Also passing of the closure struct and callback > > > function > > > becomes different and more in line with how things are done > > > elsewhere. > > > > > > Finally we keep apply_to_page_range as a wrapper around > > > apply_to_pfn_range > > > > The apply_to_page_range() is dangerous API it does not follow other > > mm patterns like mmu notifier. It is suppose to be use in arch code > > or vmalloc or similar thing but not in regular driver code. I see > > it has crept out of this and is being use by few device driver. I am > > not sure we should encourage that. > > I can certainly remove the EXPORT of the new apply_to_pfn_range() which > will make sure its use stays within the mm code. I don't expect any > additional usage except for the two address-space utilities. > > I'm looking for examples to see how it could be more in line with the > rest of the mm code. The main difference from the pattern in, for > example, page_mkclean() seems to be that it's lacking the > mmu_notifier_invalidate_start() and mmu_notifier_invalidate_end()? > Perhaps the intention is to have the pte leaf functions notify on pte > updates? How does this relate to arch_enter_lazy_mmu() which is called > outside of the page table locks? The documentation appears a bit > scarce... Best is to use something like walk_page_range() and have proper mmu notifier in the callback. The apply_to_page_range() is broken for huge page (THP) and other things like that. Thought you should not have THP within mmap of a device file (at least i do not thing any driver does that). Cheers, Jérôme
