On Wed, Apr 19, 2023 at 08:22:51PM -0300, Jason Gunthorpe wrote: > On Wed, Apr 19, 2023 at 07:45:06PM +0100, Lorenzo Stoakes wrote: > > > For example, imagine if a user (yes it'd be weird) mlock'd some pages in a > > buffer and not others, then we'd break their use case. Also (perhaps?) more > > feasibly, a user might mix hugetlb and anon pages. So I think that'd be too > > restrictive here. > > Yeah, I agree we should not add a broad single-vma restriction to > GUP. It turns any split of a VMA into a potentially uABI breaking > change and we just don't need that headache in the mm.. > > > I do like the idea of a FOLL_SINGLE_VMA for other use cases though, the > > majority of which want one and one page only. Perhaps worth taking the > > helper added in this series (get_user_page_vma_remote() from [1]) and > > replacing it with an a full GUP function which has an interface explicitly > > for this common single page/vma case. > > Like I showed in another thread a function signature that can only do > one page and also returns the VMA would force it to be used properly > and we don't need a FOLL flag. > Indeed the latest spin of the series uses this. The point is by doing so we can use per-VMA locks for a common case, I was thinking perhaps as a separate function call (or perhaps just reusing the wrapper). This would be entirely separate to all the other work. > Jason
