From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 390041DE4EC for ; Thu, 6 Mar 2025 18:42:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741286542; cv=none; b=Wswj8nxjhMXdAcI0sjhml2dORTPQ3U+Y0AX4AdhnRVQ3syq/fSbCsMMOb0LjIs1agY99FysN7cHx2sMfUxBEsYUiWIS9u82NlfiCls9+WBBHqJou5W6C4EZ8KM845CvPUUnNK7fKb4tI1F1QEkN0gF9tgpCXqAxw8/zQtFF5by8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741286542; c=relaxed/simple; bh=JDnHebyoCcnBx+cDCq/zkG7+g+ESLfON7ldIRucKy8A=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=kDDdPyePr0XRpY9LfymPVT5UZtC7xOP0CE2YFTL+J3symV/6SnhUhylnddLDLTSAIugZKSmTcDJFkmPjA2WZC8vepRkzoz24wwX+eybZth7hOdzBpZEZ4CNxHAKOK1ocJoKi0e1PGCkm41T/dT4Y+GvRwsVR0F9mpFHQJSz7Z0w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=eHYvcsys; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="eHYvcsys" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=71birkROPl9yB++m29FkJfW455fBG18HUHqmbtdCA+A=; b=eHYvcsyslBQNgH+z6Zyr8371c8 0RVewtqIv1nDnUN3e6nGgPG/MkyvcPQtWExVcHFSmGj0LLR9+BVnI/SMOSXd0opaTyNxjnNpCg5sn tZnRYCtOHTEU5shDwIqinECpZNuQnhFyCvQ2h6IInUrSWJarjtkMd9kNycQeU1YaGVmgyvir1cXtd 6d1AHUHZSQ3wsxfJUshwOq7DP6R9F4lfNxCu/iqFsf+KGhNavd6D7CGCSur/oD1mGXWjLmRnBYT5+ DgzMIuaKEu1e02W11zpnZ0Jh+mvPaKuvSHcV20VMmGS1gcx0PsWdr2k1C8CgD+ljnvVTsUab1JidW 1yWdZJvQ==; Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tqGAc-0000000B60f-1WkZ; Thu, 06 Mar 2025 18:42:10 +0000 Date: Thu, 6 Mar 2025 18:42:10 +0000 From: Matthew Wilcox To: Gregory Price Cc: Bharata B Rao , linux-kernel@vger.kernel.org, linux-mm@kvack.org, AneeshKumar.KizhakeVeetil@arm.com, Hasan.Maruf@amd.com, Jonathan.Cameron@huawei.com, Michael.Day@amd.com, akpm@linux-foundation.org, dave.hansen@intel.com, david@redhat.com, feng.tang@intel.com, hannes@cmpxchg.org, honggyu.kim@sk.com, hughd@google.com, jhubbard@nvidia.com, k.shutemov@gmail.com, kbusch@meta.com, kmanaouil.dev@gmail.com, leesuyeon0506@gmail.com, leillc@google.com, liam.howlett@oracle.com, mgorman@techsingularity.net, mingo@redhat.com, nadav.amit@gmail.com, nphamcs@gmail.com, peterz@infradead.org, raghavendra.kt@amd.com, riel@surriel.com, rientjes@google.com, rppt@kernel.org, shivankg@amd.com, shy828301@gmail.com, sj@kernel.org, vbabka@suse.cz, weixugc@google.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, dave@stgolabs.net, yuanchu@google.com, hyeonggon.yoo@sk.com Subject: Re: [RFC PATCH 1/4] mm: migrate: Allow misplaced migration without VMA too Message-ID: References: <20250306054532.221138-1-bharata@amd.com> <20250306054532.221138-2-bharata@amd.com> 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=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Mar 06, 2025 at 01:19:41PM -0500, Gregory Price wrote: > On Thu, Mar 06, 2025 at 05:45:34PM +0000, Matthew Wilcox wrote: > > On Thu, Mar 06, 2025 at 12:24:16PM -0500, Gregory Price wrote: > > > we may also need this: > > > https://lore.kernel.org/linux-mm/20250107000346.1338481-4-gourry@gourry.net/ > > > > > > May be worth just pulling these ahead to avoid conflict. > > > > Or not putting them in at all because this whole thing is a magnificent > > waste of time? > > Divorced from the tiering mechanisms, is making misplaced migration able > to migrate unmapped pages not generally useful? The only thing I can think of is if you have a process or set of processes on node A calling read() and the file is cached on node B. But in order to decide if the page is on the wrong node, you'd need to track a lot of information about which nodes the page is being accessed from. Which is probably why we've never bothered to do it. This is not a large patch for you to carry as part of your patchset. There's nothing intrinsically wrong with it; it just has no users in mainline and no real prospect of any being added soon.