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 8BF454562AA for ; Tue, 4 Aug 2026 20:02:09 +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=1785873730; cv=none; b=VN9LiZ6NP8uduk0iA06vg8g2onJSw3bb5Z8/33OyONbNEWPhEy6GKHmEg4SmkKDHgjYxP50cVRiKdAqKGaXe4ICjvtrS6rz0ORlfGvGSStz3kn1EcL1T3MgIl0OQP8dLonX/AjnZmfAmEX46oMp1sRRf3hexhPb6Mnwe8hnmTsg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785873730; c=relaxed/simple; bh=do2K381L2q14XL1PJv8YolEvgFB07Lfll+Xxn9KmzeE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=m5Z+RWmYPiIEa6Qmyn87QTlyfLfWpeI1Cvpjy30a2Ea6XElZlzZ/gPhmo+0PPnGxtnI3Lcjxpm/r5dANiTjw8r2QtHW94jJcnej0+KAt3g5tduxNz0WAmqccmcyjGpSB5Wjomg10DO7vMzXugo/1cS2fRp+ZQxV5fA/TTrFtcf0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=NcnkUECw; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass 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="NcnkUECw" 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=8oOGwlGeQFq4BNoyfaLCzUuzCLAp0LMWDRDBPkRpL9c=; b=NcnkUECwsgk/GFvFXGGMq5VR5/ u36qBE1f9hwuYUmF+dy+EnGZL6UZT9ivec52KuFbeIhcTEz89W7KVonJlBSxFGfoEQD0xj6E3+A6C 2TcQfPYMPgk/0rhlcGTkRDoOryb3tXFrL0k3IdoM+J8h3aBbTytI1Wa2f4Kf2sM8ygFk7ab19XvTs uP3vSb0Mrbti+Sv3Y8vRZwf1R1/WLMA75gLfIrqmrQjPhb7/FghZDK1ul2bkM4qeQZNW++7iobcEx Wis8zmA1iDV5VnEWw9CT8c4oI5+8CY+Otgt1p+55pXgOxbOgcFxnDhM4RJhaY8nGkKJLvioojgZR/ 2ZUx+4gg==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wrLKR-00000004eig-22vl; Tue, 04 Aug 2026 20:01:35 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id EC97830045A; Tue, 04 Aug 2026 22:01:34 +0200 (CEST) Date: Tue, 4 Aug 2026 22:01:34 +0200 From: Peter Zijlstra To: Dave Hansen Cc: Dave Hansen , linux-kernel@vger.kernel.org, Andy Lutomirski , Borislav Petkov , David Hildenbrand , Ingo Molnar , Jason Gunthorpe , Juergen Gross , Kevin Tian , Kiryl Shutsemau , "Liam R. Howlett" , Lorenzo Stoakes , Lu Baolu , Mike Rapoport , "H. Peter Anvin" , Shakeel Butt , Suren Baghdasaryan , Thomas Gleixner , Toshi Kani , Vlastimil Babka , Will Deacon , linux-mm@kvack.org, x86@kernel.org Subject: Re: [PATCH 0/3] x86/mm: DEBUG_PAGEALLOC musings Message-ID: <20260804200134.GK776954@noisy.programming.kicks-ass.net> References: <20260729110807.797920433@infradead.org> <2ea2881c-7202-40e7-8fa2-f1c649c0d445@intel.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: <2ea2881c-7202-40e7-8fa2-f1c649c0d445@intel.com> On Tue, Aug 04, 2026 at 11:34:36AM -0700, Dave Hansen wrote: > On 7/29/26 04:08, Peter Zijlstra wrote: > > my take on how we should be 'fixing' this DEBUG_PAGEALLOC thing. It appears to > > boot in qemu with debug_pagealloc=on and such things. > > The approach looks fine to me. The only thing we might want to do is add > a warning of some kind in the split/join paths for CPA_DEBUG_PAGEALLOC. So if you have lockdep enabled hitting them will scream bloody murder on cpa_lock and pgd_lock. But if you want I can sprinkle more explicit warns :-)