On Wed, Sep 08, 2021 at 06:43:49PM +0000, Liam Howlett wrote: > * Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> [210908 14:03]: > > On Wed, Sep 08, 2021 at 10:52:59AM -0700, Andrew Morton wrote: > > > On Wed, 8 Sep 2021 10:21:18 -0700 Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > > > > > > > Again I am ignorant on the details so if you can clarify the following > > > > > it may help me and others to better understand the problem: > > > > > > > > > > 1. Peter's patch appears to just take the same "fallback" path > > > > > that would be taken if the trylock failed. > > > > > Is this really a breakage or just loss of performance ? > > > > > I would expect the latter, since it is called "fallback". > > > > > > > > As Yonghong explained it's a user space breakage. > > > > User space tooling expects build_id to be available 99.999% of the time > > > > and that's what users observed in practice. > > > > They've built a bunch of tools on top of this feature. > > > > The data from these tools goes into various datacenter tables > > > > and humans analyze it later. > > > > So Peter's proposal is not acceptable. We don't want to get yelled at. > > > > > > > > > > I'm not understanding. Peter said "this patch merely removes a > > > performance tweak" and you and Yonghong said "it breaks userspace". > > > These assertions are contradictory! > > > > Peter said: > > "The only sane approach is making the vma tree lockless, but so far the > > bpf people have resisted doing the right thing because they've been > > allowed to get away with these atrocities. > > " > > which is partially true. > > bpf folks didn't resist it. There is work ongoing to make it lockless. > > It just takes an long time. I don't see how bpf folks can speed it up > > any further. > > What work are you doing on a lockless vma tree? I've been working on > the maple tree and would like to hear what you've come up with. Mainly cheering Michel and Paul from sidelines. imo any approach would be better than the current state.
