* Jason Wang (jasow...@redhat.com) wrote: > On Wed, Sep 8, 2021 at 2:32 AM Peter Xu <pet...@redhat.com> wrote: > > > > On Thu, Sep 02, 2021 at 04:22:55AM -0300, Leonardo Bras Soares Passos wrote: > > > > I don't think it is valid to unconditionally enable this feature due to > > > > the > > > > resource usage implications > > > > > > > > https://www.kernel.org/doc/html/v5.4/networking/msg_zerocopy.html > > > > > > > > "A zerocopy failure will return -1 with errno ENOBUFS. This happens > > > > if the socket option was not set, the socket exceeds its optmem > > > > limit or the user exceeds its ulimit on locked pages." > > > > > > You are correct, I unfortunately missed this part in the docs :( > > > > > > > The limit on locked pages is something that looks very likely to be > > > > exceeded unless you happen to be running a QEMU config that already > > > > implies locked memory (eg PCI assignment) > > > > > > Do you mean the limit an user has on locking memory? > > > > > > If so, that makes sense. I remember I needed to set the upper limit of > > > locked > > > memory for the user before using it, or adding a capability to qemu > > > before. > > > > So I'm a bit confused on why MSG_ZEROCOPY requires checking RLIMIT_MEMLOCK. > > > > The thing is IIUC that's accounting for pinned pages only with either > > mlock() > > (FOLL_MLOCK) or vfio (FOLL_PIN). > > > > I don't really think MSG_ZEROCOPY is doing that at all... I'm looking at > > __zerocopy_sg_from_iter() -> iov_iter_get_pages(). > > It happens probably here: > > E.g > > __ip_append_data() > msg_zerocopy_realloc() > mm_account_pinned_pages()
When do they get uncounted? i.e. is it just the data that's in flight that's marked as pinned? Dave > Thanks > > > > > Say, I think there're plenty of iov_iter_get_pages() callers and normal > > GUPs, I > > think most of them do no need such accountings. > > > > -- > > Peter Xu > > > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
