On Wed, Jul 06, 2022 at 07:31:34PM +0100, Matthew Wilcox wrote: > On Wed, Jul 06, 2022 at 11:26:35AM -0700, Alexei Starovoitov wrote: > > On Wed, Jul 06, 2022 at 07:21:29PM +0100, Matthew Wilcox wrote: > > > On Wed, Jul 06, 2022 at 11:05:25AM -0700, Alexei Starovoitov wrote: > > > > On Wed, Jul 06, 2022 at 06:55:36PM +0100, Matthew Wilcox wrote: > > > > > For example, I assume that a BPF program > > > > > has a fairly tight limit on how much memory it can cause to be allocated. > > > > > Right? > > > > > > > > No. It's constrained by memcg limits only. It can allocate gigabytes. > > > > > > I'm confused. A BPF program is limited to executing 4096 insns and > > > using a maximum of 512 bytes of stack space, but it can allocate an > > > unlimited amount of heap? That seems wrong. > > > > 4k insn limit was lifted years ago. > > You might want to update the documentation. > https://www.kernel.org/doc/html/latest/bpf/bpf_design_QA.html > still says 4096. No. Please read what you're quoting first. > > bpf progs are pretty close to be at parity with kernel modules. > > Except that they are safe, portable, and users have full visibility into them. > > It's not a blob of bytes unlike .ko. > > It doesn't seem unreasonable to expect them to behave like kernel > modules, then. If they want to allocate memory in NMI context, then > they should get to preallocate it before they go into NMI context. You're still missing 'any context' part from the previous email.
