On Thu, Mar 17, 2022 at 09:13:50AM +0100, David Hildenbrand wrote: > On 17.03.22 03:54, Alistair Popple wrote: > > Felix Kuehling <felix.kuehling@xxxxxxx> writes: > > > >> On 2022-03-11 04:16, David Hildenbrand wrote: > >>> On 10.03.22 18:26, Alex Sierra wrote: > >>>> DEVICE_COHERENT pages introduce a subtle distinction in the way > >>>> "normal" pages can be used by various callers throughout the kernel. > >>>> They behave like normal pages for purposes of mapping in CPU page > >>>> tables, and for COW. But they do not support LRU lists, NUMA > >>>> migration or THP. Therefore we split vm_normal_page into two > >>>> functions vm_normal_any_page and vm_normal_lru_page. The latter will > >>>> only return pages that can be put on an LRU list and that support > >>>> NUMA migration, KSM and THP. > >>>> > >>>> We also introduced a FOLL_LRU flag that adds the same behaviour to > >>>> follow_page and related APIs, to allow callers to specify that they > >>>> expect to put pages on an LRU list. > >>>> > >>> I still don't see the need for s/vm_normal_page/vm_normal_any_page/. And > >>> as this patch is dominated by that change, I'd suggest (again) to just > >>> drop it as I don't see any value of that renaming. No specifier implies any. > >> > >> OK. If nobody objects, we can adopts that naming convention. > > > > I'd prefer we avoid the churn too, but I don't think we should make > > vm_normal_page() the equivalent of vm_normal_any_page(). It would mean > > vm_normal_page() would return non-LRU device coherent pages, but to me at least > > device coherent pages seem special and not what I'd expect from a function with > > "normal" in the name. > > > > So I think it would be better to s/vm_normal_lru_page/vm_normal_page/ and keep > > vm_normal_any_page() (or perhaps call it vm_any_page?). This is basically what > > the previous incarnation of this feature did: > > > > struct page *_vm_normal_page(struct vm_area_struct *vma, unsigned long addr, > > pte_t pte, bool with_public_device); > > #define vm_normal_page(vma, addr, pte) _vm_normal_page(vma, addr, pte, false) > > > > Except we should add: > > > > #define vm_normal_any_page(vma, addr, pte) _vm_normal_page(vma, addr, pte, true) > > > > "normal" simply tells us that this is not a special mapping -- IOW, we > want the VM to take a look at the memmap and not treat it like a PFN > map. What we're changing is that we're now also returning non-lru pages. > Fair enough, that's why we introduce vm_normal_lru_page() as a > replacement where we really can only deal with lru pages. > > vm_normal_page vs vm_normal_lru_page is good enough. "lru" further > limits what we get via vm_normal_page, that's even how it's implemented. This naming makes sense to me. Jason
