From: Peter Zijlstra <peterz@infradead.org>
To: Andrii Nakryiko <andrii@kernel.org>
Cc: linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org,
oleg@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org,
surenb@google.com, akpm@linux-foundation.org, mjguzik@gmail.com,
brauner@kernel.org, jannh@google.com, mhocko@kernel.org,
vbabka@suse.cz, shakeel.butt@linux.dev, hannes@cmpxchg.org,
Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com
Subject: Re: [PATCH v3 tip/perf/core 2/4] mm: switch to 64-bit mm_lock_seq/vm_lock_seq on 64-bit architectures
Date: Wed, 23 Oct 2024 21:31:11 +0200 [thread overview]
Message-ID: <20241023193111.GC11151@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20241010205644.3831427-3-andrii@kernel.org>
On Thu, Oct 10, 2024 at 01:56:42PM -0700, Andrii Nakryiko wrote:
> To increase mm->mm_lock_seq robustness, switch it from int to long, so
> that it's a 64-bit counter on 64-bit systems and we can stop worrying
> about it wrapping around in just ~4 billion iterations. Same goes for
> VMA's matching vm_lock_seq, which is derived from mm_lock_seq.
>
> I didn't use __u64 outright to keep 32-bit architectures unaffected, but
> if it seems important enough, I have nothing against using __u64.
(__uXX are the uapi types)
>
> Suggested-by: Jann Horn <jannh@google.com>
Jann, do you see problems with the normal seqcount being unsigned (int)?
I suppose especially for preemptible seqcounts it might already be
entirely feasible to wrap them?
Doing u64 is tricky but not impossible, it would require something like
we do for GUP_GET_PXX_LOW_HIGH. OTOH, I don't think we really care about
32bit enough to bother.
next prev parent reply other threads:[~2024-10-23 19:31 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-10 20:56 [PATCH v3 tip/perf/core 0/4] uprobes,mm: speculative lockless VMA-to-uprobe lookup Andrii Nakryiko
2024-10-10 20:56 ` [PATCH v3 tip/perf/core 1/4] mm: introduce mmap_lock_speculation_{start|end} Andrii Nakryiko
2024-10-13 7:56 ` Shakeel Butt
2024-10-14 20:27 ` Andrii Nakryiko
2024-10-14 20:48 ` Suren Baghdasaryan
2024-10-23 20:10 ` Peter Zijlstra
2024-10-23 22:17 ` Suren Baghdasaryan
2024-10-24 9:56 ` Peter Zijlstra
2024-10-24 16:28 ` Suren Baghdasaryan
2024-10-24 21:04 ` Suren Baghdasaryan
2024-10-24 23:20 ` Andrii Nakryiko
2024-10-24 23:33 ` Suren Baghdasaryan
2024-10-25 5:12 ` Andrii Nakryiko
2024-10-10 20:56 ` [PATCH v3 tip/perf/core 2/4] mm: switch to 64-bit mm_lock_seq/vm_lock_seq on 64-bit architectures Andrii Nakryiko
2024-10-13 7:56 ` Shakeel Butt
2024-10-17 2:01 ` Suren Baghdasaryan
2024-10-17 18:55 ` Andrii Nakryiko
2024-10-17 19:42 ` Suren Baghdasaryan
2024-10-17 20:12 ` Andrii Nakryiko
2024-10-23 19:02 ` Peter Zijlstra
2024-10-23 19:12 ` Andrii Nakryiko
2024-10-23 19:31 ` Peter Zijlstra [this message]
2024-10-10 20:56 ` [PATCH v3 tip/perf/core 3/4] uprobes: simplify find_active_uprobe_rcu() VMA checks Andrii Nakryiko
2024-10-10 20:56 ` [PATCH v3 tip/perf/core 4/4] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution Andrii Nakryiko
2024-10-11 5:01 ` Oleg Nesterov
2024-10-23 19:22 ` Peter Zijlstra
2024-10-23 20:02 ` Andrii Nakryiko
2024-10-23 20:19 ` Peter Zijlstra
2024-10-23 17:54 ` [PATCH v3 tip/perf/core 0/4] uprobes,mm: speculative lockless VMA-to-uprobe lookup Andrii Nakryiko
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