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. vm_normal_page vs vm_normal_any_page is confusing IMHO. -- Thanks, David / dhildenb
