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.
The general idea of this change LGTM. I wonder how this interacts with the actual DEVICE_COHERENT coherent series. Is this a preparation? Should it be part of the DEVICE_COHERENT series?
Yes, it should be part of that series. Alex developed it on top of the series for now. But I think eventually it would need to be spliced into it.
Patch1 would need to go somewhere before the other DEVICE_COHERENT patches (with minor modifications). Patch 2 could be squashed into "tools: add hmm gup test for long term pinned device pages" or go next to it. Patch 3 doesn't have a direct dependency on device-coherent pages. It only mentions them in comments.
IOW, should this patch start with "With DEVICE_COHERENT, we'll soon have vm_normal_pages() return device-managed anonymous pages that are not LRU pages. Although they behave like normal pages for purposes of mapping in CPU page, and for COW, they do not support LRU lists, NUMA migration or THP. [...]"
Yes, that makes sense. Regards, Felix
But then, I'm confused by patch 2 and 3, because it feels more like we'd
already have DEVICE_COHERENT then ("hmm_is_coherent_type").
