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b=u4T5MVu64uZuawXIlBM7drVa70yy5BYJ2yh6jb//uLAo+4ZfEmFSzfT4UXOu0bmUw es5sSjwkUQXaXwOvvFFNNDQkkU89KRv/JEsdfiyyh/5Wyxb8NCRP0IkdEQyXedTZgf A4WLQ22J62HhIKJIa3X+2u738nfNxA9PATyYjSfw= Date: Sat, 12 Sep 2026 00:24:36 -0700 From: Andrew Morton To: Suren Baghdasaryan Cc: liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, david@kernel.org, willy@infradead.org, jannh@google.com, paulmck@kernel.org, pfalcato@suse.de, xueyuan.chen21@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v4 0/7] read proc/pid/smaps_rollup under per-vma lock Message-Id: <20260912002436.0605a85b912eb8ae406cecf0@linux-foundation.org> In-Reply-To: <20260911194145.1781926-1-surenb@google.com> References: <20260911194145.1781926-1-surenb@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: AF436C0006 X-Stat-Signature: wg1jx8tcnkfthib5eg1cq64kgngb1npr X-HE-Tag: 1789197878-271687 X-HE-Meta: U2FsdGVkX1+c74BSCBb3zasddqzVlHTcsKCGHADfVH+jT8/pvuR/xC/5TstFndTWSfroCO1iRjfpD6hdkKQzQlgiGbv2ECb0azyGNvySscVDQ+EotH+J9Fot9UQ8X2n2C0kgN6uRVCX9uTI63sxuNLv0n7eVIxQADCKLjcYPqT0BqdHxr703jZ6wV2Hh7u0PCrdXeF1iKaplJwYq2SBn7/B/R9eYwRuGjpCo+5CNW9qjsc+CBgpDPlX9KVDAulwVVHw0g5vdJMuL20UCAhG/CCQF87NlbqTBgDi7a+jjM+zYRsg15z9+Bqdz/Z8jIDxYn789+7hK+eNfb/8D/ZCOpRTzL0aKqqXKSJqlkZG1IInZmT6L0DZ+8rlG+WtOfNUrj5eJDrIUQvIy/6UAUMigodA2agJSaqWNWBVWx5E0f7Gn753RnhflBo5SPUfh5EheFVInqxc8Z3FYM6tN8i/7PVnexF830edg5IVmTFqyDYjPSUm0i1qrmd5rNGx2I5Pn1g2Flla/bwIWDdXlrV875qJEBKAqoMqao+MBuEPbDcQx26412zfCj5C/4OR0gRzgw9OXKgmrH+TkSOT3Zz1JEMbYaUw1a59I0aVACgcqAZdq/i3zC00t6wd5fVq17bKAXqgLPDKi5pWs0Nv3OxQFVT2K7JXaF8Uc0+bHYMpHLKQWOc2AOsAkOh+GfppkF7bhLFVZqYnxyz2Y0ah18RX0kh6QyojIiTAL+FF08/8TqQC7roybYfgKbwO0L4Eo6GWrOpTw40a6bxph1b+k0b7u6svxrZ/vLdEj2MW5Iz4YNZfB0lsO+KlgV8VXhp78eAtIxFOTLIMuMzxAerBMQyPrcMJbyFQQOQcWwMht7MT7mTfEa0ao68lAlg0J4l6kuUPjDXK7l4OAAWaOQEya13hW7R8/dBHDUoQ/o+ur3X2m7Oaze8gUiFJ+NxA9dC8sOXe+v/xEbz0iyKfF5MZyDax sLwPZu8r YPnqXLemySE8xg3brrNgH6ziUT5WkAazMWuW49Cr7j2Iczh23fGcKmhQ06FfHQrBWOspKtjQ38cbacBOZhNf+vLaOT3ikgK46hMR0KWkLb9MEYf1hgQdGLPR0d2ZiTqEAWaayEzOXC/V8LCyRSroiiey0XI6wjbNKRCus/Ycs0v1ANA1YHi3om1nYpvINDuSi3D+uc8sHYdSC49la7OPZyF5lahKf865mTNcJhqGdJk7Oi84zBeu+ZbrgAinmcaiqhYKgZnZHALwuoAffrEfK0QF6gUWZXvaYV+GMZQWDqJ9RJgtu35Ntv48IRfsYzjOC7biesrGGDZgh2qE+iPLznK+aukMAIxhgXj6KpFgzZUsfIEievNlo0mkSDkahlD+q4zZcodcg445Y8ZK8TdlneENr/mgl/6DrZZAL+3SykVSWMWX+32hqOj6J23Ts4yspkRhmvGSoDbbmX0U= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 11 Sep 2026 12:41:38 -0700 Suren Baghdasaryan wrote: > proc/pid/smaps_rollup can be read using the combination of RCU and > VMA read locks, similar to proc/pid/{maps|smaps|numa_maps}. RCU is > required to safely traverse the VMA tree and VMA lock stabilizes the > VMA being processed and the pagetable walk. > Note that we have to keep the logic to drop mmap_lock on contention > because even when using per-VMA locks we might have to fall back to > holding the mmap_lock. Nice. Queued, thanks. The speedups described in [6/7] are significant, although I don't know how representative Paul's tests are. Probably not very. So I don't know how much improvement our users will be seeing from these changes? And I don't know how much usage smaps_rollup gets in the real world? As I've no doubt you know, Sashiko is saying things. About these patches and about the current code. Its pre-existing clear_soft_dirty_pmd() driveby find looks significant. https://sashiko.dev/#/patchset/20260911194145.1781926-1-surenb@google.com