On Wed, Jul 06, 2022 at 07:40:44PM +0100, Matthew Wilcox wrote: > On Wed, Jul 06, 2022 at 11:36:19AM -0700, Alexei Starovoitov wrote: > > 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. > > I did read it. It says > > : The only limit known to the user space is BPF_MAXINSNS (4096). It’s the > : maximum number of instructions that the unprivileged bpf program can have. > > It really seems pretty clear to me. You're saying my understanding > is wrong. So it must be badly written. Even now, I don't understand > how I've misunderstood it. huh? Still missing 'unprivileged' in the above ? and completely ignoring the rest of the paragraph in the link above? > > > > 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. > > Really, this is not a productive way to respond. I want to help > and you're just snarling at me. To help you need to understand what bpf is while you're failing to read the doc.
