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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1t3gcz-00000008Wsk-0r4w; Wed, 23 Oct 2024 19:02:41 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 8E96430073F; Wed, 23 Oct 2024 21:02:40 +0200 (CEST) Date: Wed, 23 Oct 2024 21:02:40 +0200 From: Peter Zijlstra To: Suren Baghdasaryan Cc: Shakeel Butt , Andrii Nakryiko , 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, akpm@linux-foundation.org, mjguzik@gmail.com, brauner@kernel.org, jannh@google.com, mhocko@kernel.org, vbabka@suse.cz, 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 Message-ID: <20241023190240.GA11151@noisy.programming.kicks-ass.net> References: <20241010205644.3831427-1-andrii@kernel.org> <20241010205644.3831427-3-andrii@kernel.org> <55hskn2iz5ixsl6wvupnhx7hkzcvx2u4muswvzi4wuqplmu2uo@rj72ypyeksjy> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: 5AE2EC0028 X-Stat-Signature: bhdy18dzs66fqxakrj97sa1pb9afunhg X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1729710151-45308 X-HE-Meta: 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 WLy+Zrlq h2Hz9GO42PaDIAOzigxG78Njr9dW6PHV7+5iGAxL6uWu8s5KIP3UuvTIOdkweZt9W97RqKi46leXy/fC7JFmNG+wYVb2rgAwRnQcsRfR9NhYinsBEs/ctfjd50x8r4wWXW12Ro2mPv/NGYB3YimdqSSkh0wd7D8a/pzOtlj4CUqAMR6s7bZIBUQWwWRF87x0I8qJbj3+wuyZpkyPF9jxlzXlX+Ifmkw/dY2F/yyNeSkN5eLI3DHTFXa4o73XRv296PL9nZSwVT8X0C6Q= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 16, 2024 at 07:01:59PM -0700, Suren Baghdasaryan wrote: > On Sun, Oct 13, 2024 at 12:56 AM Shakeel Butt wrote: > > > > On Thu, Oct 10, 2024 at 01:56:42PM GMT, 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. > > vm_lock_seq does not need to be long but for consistency I guess that > makes sense. While at it, can you please change these seq counters to > be unsigned? Yeah, that. Kees is waging war on signed types that 'overflow'. These sequence counter thingies are designed to wrap and should very much be unsigned.