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From: Andrew Morton <akpm@linux-foundation.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Luigi Rizzo <lrizzo@google.com>, Yonghong Song <yhs@fb.com>,
	Liam Howlett <liam.howlett@oracle.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Michel Lespinasse <walken@google.com>, bpf <bpf@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	"kernel-team@fb.com" <kernel-team@fb.com>
Subject: Re: [PATCH mm/bpf v2] mm: bpf: add find_vma_no_check() without lockdep_assert on mm->mmap_lock
Date: Wed, 8 Sep 2021 10:52:59 -0700	[thread overview]
Message-ID: <20210908105259.c47dcc4e4371ebb5e147ee6e@linux-foundation.org> (raw)
In-Reply-To: <20210908172118.n2f4w7epm6hh62zf@ast-mbp.dhcp.thefacebook.com>

On Wed, 8 Sep 2021 10:21:18 -0700 Alexei Starovoitov <alexei.starovoitov@gmail.com> 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!

Please describe the expected userspace-visible change from Peter's
patch in full detail?

And yes, it is far preferable that we resolve this by changing BPF to
be a better interface citizen, please.  Let's put those thinking caps on?

  reply	other threads:[~2021-09-08 17:53 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-08  4:44 [PATCH mm/bpf v2] mm: bpf: add find_vma_no_check() without lockdep_assert on mm->mmap_lock Yonghong Song
2021-09-08 12:20 ` Daniel Borkmann
2021-09-08 13:53   ` Jason Gunthorpe
2021-09-08 14:15     ` Peter Zijlstra
2021-09-08 14:43       ` Luigi Rizzo
2021-09-08 14:43         ` Luigi Rizzo
2021-09-08 15:12         ` Liam Howlett
2021-09-08 16:09           ` Yonghong Song
2021-09-08 17:09             ` Luigi Rizzo
2021-09-08 17:09               ` Luigi Rizzo
2021-09-08 17:21               ` Alexei Starovoitov
2021-09-08 17:52                 ` Andrew Morton [this message]
2021-09-08 18:02                   ` Alexei Starovoitov
2021-09-08 18:15                     ` Andrew Morton
2021-09-08 18:20                       ` Alexei Starovoitov
2021-09-08 18:20                         ` Alexei Starovoitov
2021-09-08 18:30                         ` Liam Howlett
2021-09-08 18:45                           ` Yonghong Song
2021-09-08 18:49                           ` Jason Gunthorpe
2021-09-08 19:11                             ` Yonghong Song
2021-09-08 23:33                               ` Jason Gunthorpe
2021-09-09  5:50                                 ` Yonghong Song
2021-09-09  8:05                           ` Peter Zijlstra
2021-09-08 18:43                     ` Liam Howlett
2021-09-08 19:42                       ` Alexei Starovoitov

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