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=1793978666; b=2g8I5IdprTJhecWtUk9HxnRasO9jzt/6uraD6qj8YAprTkY4WltjKviy8C7/FunP4Qzl 7ma+Jf3VvQ0sPlFoe8sm2S4IZK4LhbkXPgweYIHaijlWUCg4RV7tG54R5dt3bpQcbwq0/ gYHHtZ1/TbEVg17cgnhsPF0wT2EuS9B2PvZHSDI6zAXPuS/Z2JvRNrJUzDm2g7I68Hh0k pGR65lZLb573lsanlzf76VO0awOLWPlrbkEZkhV7vHR1gYfopV943O77xWACJXMl4t8g5 9oLIJktQ9OcKOp0OSpdjE90RPcEC/QYsC8EMqj7sm7ytqeLz9VrRbF8ZZfX2rpm12Bg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793978666; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=TLgNyXFrGS0TryALTyECIzzY5cEQxpys9ixb+i595LQ=; b=NrcZK3qauMCBMJQ7ueSpiwcan6f8Zydol5azxPNGbbTZ3uJjj58dqrzOJzCTx3FFKW7i 6/+XFhIDd0+X2XxrHClby9q5yfUeGWNRZUxzjjdKkUoHP6Adu6t4kPCNU7xu2B7MNVCPX pP4wah9ZLHxP6LTeVJvmL5obVKrhYL/gtxOxRR0x5LWE1Ni1/zlmP84NTgEdZf1W/BL3T BSWDt5i+0HSg/QsSa3ytDTDDhZXkFqHBvfns/ZAGzkevvU4ModYdfC/5F70UuNzYUVEfE P3YhAfrW+6ts7VCRwP1J3xzw819ngcaEeGsoW1xjU2izLW1VGjH6nKbBxz9Q8tWH4og== 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=E9dNbIMv; 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 5A5A6606A331 for ; Fri, 6 Nov 2026 15:24:26 +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=E9dNbIMv Received: by smtp.kernel.org (Postfix) with ESMTPSA id D538B1F0089F; Fri, 6 Nov 2026 15:24:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793978666; bh=TLgNyXFrGS0TryALTyECIzzY5cEQxpys9ixb+i595LQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=E9dNbIMvKrV4r7KYAGyHcAcgMkbVi7NVeGv74QZS6YsZpCAawM3rJyKrzu0kGUmoR Bj/DAcnTvVZR1djvBU9Lg3QVTY5LCV5uAawidByHA+Ke5JNXq5LeZ6zopldNKKlpKo QZKc90oVLJgkOm0eDLkALAvGz2ocxyqEugxe5zKZc550TuDT6jOZBCOdFNbPijdy+f HJris1dK2k20jvpzqMEVCuPzLq3CWHKZYiqMDQvvlOhke4+5fCFu8sT++gBEPE6aj8 tCdFDNSeX2ABRCxwuoO3Pm/1oR9uq4MerdTgx8flrWHgSzBy7gvU6RusFUM85qyq0D Z0TJT2KFPERkw== Date: Fri, 6 Nov 2026 15:24:20 +0000 From: "Lorenzo Stoakes (ARM)" To: Vernon Yang Cc: 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 , 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> <798cd192-9ec2-4f37-9cba-44db275a269c@gmail.com> 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: <798cd192-9ec2-4f37-9cba-44db275a269c@gmail.com> On Fri, Nov 06, 2026 at 09:26:01PM +0800, Vernon Yang wrote: > On Fri, Nov 06, 2026 at 12:07:53PM +0000, Lorenzo Stoakes (ARM) wrote: > > 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. > > Looks good to me. Is the test result of this solution the same as the > current one? Thanks! I will update the commit to reflect the changes. > > -- > Cheers, > Vernon -- Cheers, Lorenzo