On Tue, Mar 18, 2025 at 03:47:31PM +0100, Hannes Reinecke wrote: > 'Warming up to frozen pages' > With the frozen pages patchset from Willy slab pages don't need > (and, in fact, can have) a page reference anymore. While this easy > to state, and to implement when using iov iterators, problems > arise when these iov iterators get mangled eg when being passed > via the various layers in the kernel. > Case in point: 'recvmsg()', when called from userspace, is being > passed an iov, and the iterator type defines if a page reference > need to be taken. However, when called from other kernel subsystems > (eg from nvme-tcp or iscsi), the iov is filled from a bvec which > in itself is filled from an iov iter from userspace, so the iov > iterator will assume it's a 'normal' bvec, and get a reference for > all entries as it wouldn't know which entry is a 'normal' and which > is a 'slab' page. > As Christoph indicated this is _not_ how things should be, so > a discussion on how to disentangle this would be good. > Maybe we even manage to lay down some rules when a page reference > should be taken and when not. My only concern is that we might not have anybody from networking to talk about their side of all this. We need Dave Howells for this as one of the network filesystem people, he probably understands this fairly well. Anna might have some network stack knowledge too. Maybe we can get some of the BPF people to join in; although their track looks very dense, so we'll have to try hard to find a time when there's a topic that the networking-BPF people aren't so interested in.
