From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AA2D944A724 for ; Wed, 15 Jul 2026 12:40:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784119245; cv=none; b=pIUSp5IKnq0JM7Ms1WpCGcn/0CF1z8orxJ6D78licxa4iB0lCOcPUlXYZVwituxOMSCgv0JYpBK7OuLBOpTFwh7vcHbpUQydNTci8LVQlUHUz7SeNZ7ron/S3yGx+pTgZ5p2vVpo7VXOhWoIbVDZLJZ6jnnClNkhYbezvkZtBDk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784119245; c=relaxed/simple; bh=F7n5G2T6DO3SJutvzCM2C+HWnvX7xf3B7tx9zmMEADs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YGTQHwgLitZYtImqZRq6YSOy7O11y2luh2lfiZ3n2t/AwjAihXcjzpfA6TubwlsdHswsxaztmc/9EbebWiAGVhUrbTXjwdoTmUzja6Sa1cLKSdbvm96coE43A9vpnQh3h4LQAJdW7lXjNzwbHc98i3TjRvNxma9O9C6v0oN/pzQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=R/+DW4Qs; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="R/+DW4Qs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1470A1F000E9; Wed, 15 Jul 2026 12:40:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784119244; bh=i70MI3s/daHgb9WcIfx/WVMuhZ4GwOjC+i/kHkbzay8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=R/+DW4QsHagJtrTm/PTF1fKFkQUwn2RCbCtKWbYz32A5aQmLRXgW0gznkbmzP//tx 8wh8fGPqa+d90N7VKYCtVtrpkSTggPM4uj8Hg8EPVH9x+mjALJBzvrazvWN2J5MX1l epqL0VPTJr6z6ia/yLeoW/JNUQ8zmIjRDW6gxICJvzVJeqtgOUkQw1SJ/gkEJIM/Rr wbwFkdjJZaQ8qS1eF8FKkxSvz1nYKrbKum038JZNG412M/6b88ltOpD2mHwv2c5MB2 k+ZOISYGwdB0CUMoaOYAoHnCIe6nwYqOmRjegD1qW3p3xpnswgQPW/raFCWgAfFIfF /aXPl5Id2ry3A== Message-ID: <8f7f0a6f-d819-4a56-bb5c-d690664dd80e@kernel.org> Date: Wed, 15 Jul 2026 14:40:40 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate_device: avoid overflowing migrate_vma collection arrays To: Zi Yan , Alistair Popple , Balbir Singh Cc: Matthew Brost , Andrew Morton , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Kefeng Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko References: <89d20411-4915-43e8-9808-3a7fbd98d2ab@kernel.org> <57cc487b-6ec3-4ca6-8735-f37644e2b0ab@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/15/26 02:59, Zi Yan wrote: > On Tue Jul 14, 2026 at 1:30 AM EDT, Alistair Popple wrote: >> On 2026-07-14 at 10:10 +1000, Balbir Singh wrote... >>> >>> I had a patch to add tracepoints to the code and some of that instrumentation >>> included this data. A combination of the trace points + hmm_tests will help us >>> get some data to start with. >> >> But hmm-test already has a nice bandwidth benchmark :) We just need to force >> the slow path. That used to be easier before I simplified the trylock handling >> but with the below patch applied I get quite a lot better perf from the >> optimisation. Note the patch isn't entirely correct as it assumes any locked >> page was locked by migrate_vma_collect_pmd but it's good enough for the purposes >> here. > > Thanks for the numbers. If I read them correctly, the optimization > has about 3x throughput of unoptimzied version. The optimization has to > stay. > > I will try to come up with a fix that resets collected PFNs, reverts > established migration entry along with putting folio ref, and restarts > from the beginning. IIUC, with the page table gone there are no entries to revert. We only have to take care of folio lock+ref. Which raises a question: how can the page table be gone when it contained migration entries? Probably MADV_DONTNEED could clear them, followed by reclaiming the page table, maybe. -- Cheers, David