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 C74A81F5F6 for ; Sat, 1 Feb 2025 14:04:23 +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=1738418665; cv=none; b=Wloj/gY0Zoz8sJb/uE2G9Ga4SBjlqLhLO3TKidbYOBCJqa2H+GZ4649egOzivzQu0vtkzbB/Enbn11EtPs2AsYV/FxPDZ8eg95TCLIUZ7J6yfTPSKC0HeuwqLsTdqXQ8hMUkH0pfOFq8FUkOWRA+tQ9W55swuG7bLwouB8Gu5+I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738418665; c=relaxed/simple; bh=ImF5bNWRDx+GmA1NSeCPZ113ytFRv3UOoDTpwe2uLGg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rBEYZvHDOMTvL9gkAN7IjF1ERZCGlsLp2Qg8ValdQ6hX7KINhriktBwWUvgaH240TdbzynpebMkBvUVgni2SlD/rxWXKAn+4oa05E2JTrXa9B5l4EwCnmlUPFpCr/fSQmzCNwmj1Fw8I6EpVZtrDllBbJkRBftDcs+M5bUwH360= 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=eGIUcCma; 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="eGIUcCma" 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=bJ1G7pUr3By7yXgMdoF7Bkl84Q86WzINHDB+IDr7o2E=; b=eGIUcCmaIpAMR9ArfLy53FnTuB D8tqnMnjZnszG8OOcjlmEIvb7chkPQQppUAdN8Z21YY79MlQ1cZZ/zSuZlRneOuWKuttdXl5I4lj0 qmnmMYJaFMlfP5e7F3AL3fjVutqEhhJvGS80DIXHPVdSVJd00vMycIO9Gh+bMTAyRPxho99pbVwdm SH1OKTO52ivjxd7KY9imPDRFReC0lmZhRCeIK78Jn3vsPBAdIicV1rds29A6W4ASUzIo38bs8rBhY MEb6glAvzQeTQviJaROg917g2O4vd/51c81QLizKc74umqwQLEMD3ypGlDb1eJkCBM00lGGcAgPY7 TyHQ0OtA==; Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1teE6b-0000000G6LV-3WyH; Sat, 01 Feb 2025 14:04:18 +0000 Date: Sat, 1 Feb 2025 14:04:17 +0000 From: Matthew Wilcox To: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org, Byungchul Park , Honggyu Kim Subject: Re: [LSF/MM/BPF TOPIC] Restricting or migrating unmovable kernel allocations from slow tier Message-ID: References: Precedence: bulk X-Mailing-List: linux-cxl@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 Sat, Feb 01, 2025 at 10:29:23PM +0900, Hyeonggon Yoo wrote: > The Linux kernel supports hot-plugging CXL memory via dax/kmem functionality. > The hot-plugged memory allows either unmovable kernel allocations > (ZONE_NORMAL), or restricts them to movable allocations (ZONE_MOVABLE) > depending on the hot-plug policy. This all seems like a grand waste of time. Don't do that. Don't allow kernel allocations from CXL at all. Don't build systems that have vast quantities of CXL memory (or if you do, expose it as really fast swap, not as memory). All of the CXL topics I see this year are "It really hurts performance when ..." and my reaction is "Yes, I told you it would hurt and you did it anyway". Just stop doing it. CXL is this decade's Infiniband / ATM / (name your favourite misguided dead technology here). You can't stop other people from doing foolish things, but you don't have to join in. And we don't have to take stupid patches.