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 1211B3126C0; Thu, 1 Oct 2026 10:55:22 +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=1790852127; cv=none; b=VqXa/1JwExbLG9Le1aKLgn6zvZYxF4/BkDHoKWCskuqzweEhmI274YzUW1+FNFeIiIm66CMLMM5zFPew3qr5wOUBHlApZ6j+aku0fvY1L06d31e9VQu5QY/LuQKkWfDRvX9lydmja+LA+8Cgzz2omoLxHQILaryFUacpoJ4BYQY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790852127; c=relaxed/simple; bh=TLPWu9ylXvUEH9lTGZQeERfKWCMekd+zu9v9tsZD52s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lDlz/dAYi1ODB1BSU5uB3loVmQJyo5Ecs8V2yxcdqLh+2UaRp+3jeh+JrnFrkQWwDW/BYqJbY7UKdQ/s38q4ZD46tFfIeYoBQu2mbtPUHFvtDtJ1ZlnNhNLUFZDBJS2DCHQ1YZiOXUHW/RI8YzOp9MgTjMdz+HsD95IeX0/6BwA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OfncYfp3; 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="OfncYfp3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D63FE1F000FF; Thu, 1 Oct 2026 10:55:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790852119; bh=penxqr9i9OBDqzR9Qzq1r2NHVsP0bv2yCQX2PsmhJ8k=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=OfncYfp3EtQ5vNQxUvpMVGVjy20dPvbDUZVeNjZTTIBBMgw+tVr5rRcNDAJqCM/PX A4MFsfzdj/e6giw52AZedON5aXr2t+tm3elUaBz7JDaimwLGKWwEhopgwzT9elam+Z r2jAMWZWdkpgCQBTpYhE3WvmlOjNA7Xba3VRUl6r66KvqVary9j/kFBhvR0c5Uij0s NhcEavOdPUuFaQ7tSOYFKJ7Qfad13KoFQiB8BvoQX1yg4DWTwTwkpa9badb9d8MiLk w5W6t9g3nngB9eO+QwuatNiWEahkhk9hTZmgFxteQI2y7KwWgzD2cmE+BSKnD+w5gw RxQn38HVyRYZA== Message-ID: Date: Thu, 1 Oct 2026 12:55:12 +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/numa_balancing: allow migrate on protnone reference with MPOL_WEIGHTED_INTERLEAVE policy To: Gregory Price Cc: Li Zhe , akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, mhocko@suse.com, corbet@lwn.net, skhan@linuxfoundation.org, ziy@nvidia.com, joshua.hahnjy@gmail.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260930072617.64665-1-lizhe.67@bytedance.com> 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 9/30/26 15:40, Gregory Price wrote: > On Wed, Sep 30, 2026 at 02:32:16PM +0200, David Hildenbrand (Arm) wrote: >>> >>> Right, but you're requesting this configuration. If you didn't set >>> F_NUMA_BALANCING then you get the existing semantics. >>> >>> In the existing semantics, if we're INTERLEAVE and WEIGHTED_INTERLEAVE >>> we just always say "no tiering for you". >>> >>> But as an opt-in option? I don't quite see the argument for saying >>> interleaved regions (or tasks) to be opted-out if the user asks for it - >>> that just seems like an arbitrary limitation. >> >> Just to be clear, what I am saying is: the proposed semantics are inconsistent >> (weighted when mechanism A honors them and mechanism B doesn't honor them), but >> once we set these semantics in stone like that, we cannot easily change them >> later because some user might depend on that behavior. >> >> So you'll need yet another flag to say "NUMA balancing really also honors the >> weights". And that's where it all gets ugly. >> > > I would agree with you if demotion didn't entirely ignoring mempolicy. > > On a tiered system, mempolicy *only* applies to initial (or fault-in) > placement, and otherwise is more or less entirely ignored. This is > a case where it's not ignored - which is actually inconsistent with > the rest of the tiering tools (demotion, damon). > > This is why I said this distinction may only make sense in TIERING > mode, while in NORMAL mode you likely just want to fault it back to > its original interleave location. > > Also file interleave (indexed by offset) vs task (counter-incremented) > policies are affected by these changes very differently, which I asked > for some thought on. > > As tiering develops, the less I think task-mempolicy as a whole makes > much sense (because it's at-best advisory). Fully agreed to that. I even struggle to understand how an initial placement using the weighted policy really fits into that picture. -- Cheers, David