On 26.01.22 15:12, Matthew Wilcox wrote: > On Wed, Jan 26, 2022 at 02:55:10PM +0100, David Hildenbrand wrote: >> On 26.01.22 14:38, Matthew Wilcox wrote: >>> On Wed, Jan 26, 2022 at 11:16:42AM +0100, David Hildenbrand wrote: >>>> A while ago I talked with Peter about an extended uffd (here: WP) >>>> mechanism that would work on fds instead of the process address space. >>> >>> As far as I can tell, uffd is a grotesque hack that exists to work around >>> the poor choice to use anonymous memory instead of file-backed memory >>> in kvm. Every time I see somebody mention it, I feel pain. >>> >> >> I might be missing something important, because KVM can deal with >> file-back memory just fine and uffd is used heavily outside of hypervisors. >> >> I'd love to learn how to handle what ordinary uffd (handle >> missing/unpopulated pages) and uffd-wp (handle write access to pages) >> can do with files instead. Because if something like that already >> exists, it would be precisely what I am talking about. > > Every notification that uffd wants already exists as a notification to > the underlying filesystem. Something like a uffdfs [1] would be able > to do everything that uffd does without adding extra crap all over the MM. I don't speak "filesystem" fluently, but I assume that could be an overlay over other fs? Peter is currently upstreaming uffd-wp for shmem. How could that look like when doing it the fs-way? -- Thanks, David / dhildenb
