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Sun, 07 Jun 2026 20:32:09 -0700 (PDT) From: Cunlong Li To: SeongJae Park Cc: Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/damon/vaddr: drop redundant mmap_read_lock from damon_va_three_regions Date: Mon, 8 Jun 2026 11:32:05 +0800 Message-Id: X-Mailer: git-send-email 2.30.2 In-Reply-To: <20260607173644.93883-1-sj@kernel.org> References: <20260607-rcu-v1-1-3c9f5995a3a0@gmail.com> <20260607173644.93883-1-sj@kernel.org> Mail-Followup-To: Cunlong Li , SeongJae Park , Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Sun, Jun 07, 2026 at 10:36:44AM -0700, SeongJae Park wrote: > Hello Cunlong, > > On Sun, 07 Jun 2026 21:48:52 +0800 Cunlong Li wrote: > > > __damon_va_three_regions() already walks VMAs under rcu_read_lock(), so > > the outer mmap_read_lock() is no longer needed. > > The function aims to read a snapshot of the virtual address space. So I think > mmap_read_lock() is still required. Please let me know if I'm missing > something. > > > Thanks, > SJ > > [...] Yes — I understand this path is meant to obtain a snapshot of the VMA layout. My thinking was that an exact snapshot may not be required here, and the RCU-protected traversal inside __damon_va_three_regions() already makes the walk safe, so the outer mmap_read_lock() might be redundant. But, if we want a consistent VMA layout here, mmap_read_lock() is the right mechanism and rcu_read_lock() alone is not enough. I'll drop the patch :) Thanks, Cunlong