From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793966880; b=w/+IlBd8CxzVZxb4G6JmylCiX1PT8qBTmIu1ik+oTcdL5l0Uj1THC/p/39/SLCfX+8Dk hhCKRTF8E1KodSKDcJZdjLSyosi1htZxHdkbtjvt6wVsHyUbvkZFtLHdZln/OKz7XNAdC c51r4udO07WjK8ZTUJ2NDmIKWm0jUGgNVKiAg6vIYWfRcWYXatsVAMq8A30pvdagFTiYY fD5bvXDuZTN/wazJZzMH1jiaKYhOw9wvOYDX1fgKVlxI3ROLaYbz66ZERcGZBzR/RHYp6 /Cu84BN7c/+xE0BKKIZKqEKII86Fl5Msjs5/BcgZ4wpZ74oXKa8vOqfvyDRNAylpJgw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793966880; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=/46L68pR/Enc7fYZWiScuGH0LLWYaias1sdt7wy84ms=; b=s120iOnqVmoKGNM3yqgE/3M9azCXSVLu5lBq8azmk1OpLefVyii4K9DNsIVdHlHwuJ/b HsiMJBjnBYUydUOfGcFekE1MbXhGp7GXH8bdwLHqVi9AGP0c3Xy0UNQjXyTANFE0KQzY8 K8PvGtIsqMzb5NhNdii38C2W3HEDri6k1jIRHTHw8g4TbUjeaB2HUPvXVQjShaE37IdKc vQ3N8isNRjSMqIrHVLrehs/HKu/pd0cXO3OIDMjhYpyi16RUvrh1BgGz8nH6Gd1gXx0x0 9gzpDRL1pYFeSXKuecbU9Sg09hnLACDv0Qi3Tf1J7qldCct0haNlBuhik8u2Fqwcmkg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=mlejMS7C; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BF357606A32F for ; Fri, 6 Nov 2026 12:07:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=mlejMS7C Received: by smtp.kernel.org (Postfix) with ESMTPSA id 745691F0089F; Fri, 6 Nov 2026 12:07:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793966879; bh=/46L68pR/Enc7fYZWiScuGH0LLWYaias1sdt7wy84ms=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=mlejMS7CjxEq6jLLSwGu7+ysqSsfyEJ4AJdWyZJ9nSJU4SnRD6iThs3XrN2kJ7IPb oDp25jS3hyilaFDlrWAVkjiV0qaFN0V+Umpx2iKYALD+k4OUd4b0GW9SgaiN1zuulK lEq8ySrhvWAIHlzWeo7Ls9+4B8AZly6D2Zp7WsDxcNutGMRCypKoPPNdQTjtiaY8jE Q4m6eXuOXyFETQwcsSAonYMybHSWF74xujXfx0fa07vNxuHTMIWYjeov1/igY2aOr1 azCsgQ8deblzykTCs5kLWGlo/r8FTSvvZ2xiYOx3cTjBZg+HkeRpdMJm+4BJHI3Ts+ HbXCANfb5C7Ag== Date: Fri, 6 Nov 2026 12:07:53 +0000 From: "Lorenzo Stoakes (ARM)" To: David Hildenbrand , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/3] mm/khugepaged: release contended mmap read lock after scanning enough VMAs Message-ID: References: <20261105-khugepaged-latency-fix-v2-0-4384bbfe4606@kernel.org> <20261105-khugepaged-latency-fix-v2-3-4384bbfe4606@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261105-khugepaged-latency-fix-v2-3-4384bbfe4606@kernel.org> On reflection, I think this would be better implemented as something like: static void collapse_scan_mm_slot(unsigned int progress_max, ...) { unsigned int long lock_start = jiffies; ... for_each_vma(vmi, vma) { ... if (time_after(jiffies, lock_start) && mmap_lock_is_contended(mm)) { mmap_read_unlock(mm); cond_resched(); mmap_read_lock(mm); lock_start = jiffies; vma_iter_set(&vmi, mm_slot->address); continue; } } } Which avoids magic numbers, and means if we hold the lock for 1-10ms (depending on HZ), which is a long time in the kernel to hold a lock, AND the lock is contended, we drop/reacquire. -- Cheers, Lorenzo