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b=UQMYV3ZKcZd4PTfDuCGUUCmHgppui9/Vm/kGrVy0q6tnmbMql5N9huBmxl8OhHmPq NZXe7O+u4nVXHvTE/mXhF7eqPUUxLaqX+2FACM1qI2tTOBZxU7lhh3Fy2moNpxgsT3 DKt/0Y/mqQ+5TDNs4DWalqXQ2Efn0bhAzIRdX/ox5/QrhL3riv8HF6k+l8OVLy0zvv CBUN1Xjy3S/ddU+RTWxf4YFyACT+c+NQhxHW+dgeTe3NPW5pf9hCSHwWDo0DTkFDPg JOEP8qewIj059PxVLOsFuAwy8nEh6oDYCqOHRb/+2poEJhV7mK06Gg8Cg4w6vRLym8 6hg3qeubdPNWw== Date: Thu, 28 May 2026 16:37:01 +0100 From: Lorenzo Stoakes To: Andrew Morton Cc: Suren Baghdasaryan , "David Hildenbrand (Arm)" , liam@infradead.org, vbabka@kernel.org, willy@infradead.org, jannh@google.com, paulmck@kernel.org, pfalcato@suse.de, shuah@kernel.org, hsukrut3@gmail.com, richard.weiyang@gmail.com, reddybalavignesh9979@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v2 0/3] use vma locks for proc/pid/{smaps|numa_maps} reads Message-ID: References: <20260426062718.1238437-1-surenb@google.com> <0ce6071b-0c99-4119-9ab4-a2d9c00b99a8@kernel.org> <20260526184944.18c28d6980fd29ff12fbbe22@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260526184944.18c28d6980fd29ff12fbbe22@linux-foundation.org> X-Stat-Signature: 1eg6qx5bkpe5ehmt818cnttiygyh9tih X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BA2334000B X-Rspam-User: X-HE-Tag: 1779982629-504378 X-HE-Meta: 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 Lppefrq7 ThUXRFT1bjsv+akidYtB0PwcfZMG69rp9Y5x6jJg0P7NWrkElQVaM9sKz8mk9WGtnYjUbHrnmd4u5y2aB1eLzsETx+FXHkzqDwt8aS+RvJNxn0rcyeUfOehClP3vf9uah0K7jNvsblpyNuBXQcVFdJ05Wtk4pEJapJa3pyL4cofDK/R2X2BHYIc21WbszpcA6DFBpGJNkD/fUdlZN3Zd95Y32odyMMlP0YsEgpKbhAbsbzRRkxqSswz70dBm59fFYbi2iTTL3UrYhkaXdlN4XmSeEJBNLrd9iK1wogg62NqcqfBW2eLlBDMNLRgFAJbDCcZDPPG3gn+KjfrJI66mLbVCvwIc2lwsH26bFdGiZcku3nVxWSZYQZYetqbQ3Ult2mol0fDp9j8u/eLaZBFIFJA90DW2d3ujSbXIoUAsk9In4KKXqhzxJGw6BsuP8ukwt4ROs Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, May 26, 2026 at 06:49:44PM -0700, Andrew Morton wrote: > On Thu, 21 May 2026 08:16:01 -0700 Suren Baghdasaryan wrote: > > > > > It might be but the point of this patchset (and the previous one that > > > > made a similar change for /proc/pid/maps) is to reduce mmap_lock > > > > contention, not to speed up the read operation, which is not a > > > > performance critical part. > > > > > > Well, this interface has been around .. forever, so if there is a noticeable > > > change in performance it should be called out. > > > > Sorry, I missed your reply. I'll see if I can adopt Paul's test for > > /proc/pid/maps [1] for benchmarking smaps but I would expect similar > > results as was reported in [2]. > > How's it coming along ;) > > > [1] https://github.com/paulmckrcu/proc-mmap_sem-test > > [2] https://lore.kernel.org/all/20250719182854.3166724-1-surenb@google.com/ > > I've moved this series to the tail of mm-unstable to permit more time. Well I'm not sure it's _vital_ to get stats for this, it's pretty much an extension of existing VMA lock work in /proc/$pid/maps -> smaps, and the logic is sound. There's no reason to believe there will be anything other than a reduction in lock contention here at least under whichever workloads happen to hammer smaps, but doesn't feel like there's a downside! Cheers, Lorenzo