From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 702D0CA0FE7 for ; Tue, 26 Aug 2025 13:39:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=o0dIKLq7mMxlWwZyWFQYffTfikp/TwVGT+xrqhNBlKs=; b=2UO5TYqjiP5nKRbI2MH8CDk1nD EGUsBwK7tmvNp9QVq2jnG1l5dTulZNmA/h0hENuiaWpHNxdR94VtuACqQj1LD0udhX5wDSKSMrzyE me/JuouLCMu5ev+rC1HQwQeHdPVPf4qkImbEzhwLuPz0rmtDx4eo7Kx4l1iGerb19QUJ4GiGDYoV4 SkIvECJjmwPE6GZGgwZvLoPAuzpI8Lh/9hFse/OGUenXK7gHfRrL0hRt2hBnnJtqnxicngj/N5Pvq KZlK+GfOLsOPtwgxWXl3AKzQn+WEMMYVTwBsEk5N9wny5k8NS5ZhdVMgAgBOTZSwfZuQFUnOivL4Y pp194e0g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uqttb-0000000C863-3Sp6; Tue, 26 Aug 2025 13:39:31 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uqtSj-0000000C3MC-1shr; Tue, 26 Aug 2025 13:11:46 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7C1B82BF2; Tue, 26 Aug 2025 06:11:36 -0700 (PDT) Received: from raptor (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0B7A13F63F; Tue, 26 Aug 2025 06:11:36 -0700 (PDT) Date: Tue, 26 Aug 2025 14:11:34 +0100 From: Alexandru Elisei To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Alexander Potapenko , Andrew Morton , Brendan Jackman , Christoph Lameter , Dennis Zhou , Dmitry Vyukov , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, iommu@lists.linux.dev, io-uring@vger.kernel.org, Jason Gunthorpe , Jens Axboe , Johannes Weiner , John Hubbard , kasan-dev@googlegroups.com, kvm@vger.kernel.org, "Liam R. Howlett" , Linus Torvalds , linux-arm-kernel@axis.com, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-ide@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, Lorenzo Stoakes , Marco Elver , Marek Szyprowski , Michal Hocko , Mike Rapoport , Muchun Song , netdev@vger.kernel.org, Oscar Salvador , Peter Xu , Robin Murphy , Suren Baghdasaryan , Tejun Heo , virtualization@lists.linux.dev, Vlastimil Babka , wireguard@lists.zx2c4.com, x86@kernel.org, Zi Yan Subject: Re: [PATCH RFC 21/35] mm/cma: refuse handing out non-contiguous page ranges Message-ID: References: <20250821200701.1329277-1-david@redhat.com> <20250821200701.1329277-22-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250826_061145_586257_4E10FF5A X-CRM114-Status: GOOD ( 27.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi David, On Tue, Aug 26, 2025 at 03:08:08PM +0200, David Hildenbrand wrote: > On 26.08.25 15:03, Alexandru Elisei wrote: > > Hi David, > > > > On Tue, Aug 26, 2025 at 01:04:33PM +0200, David Hildenbrand wrote: > > .. > > > > Just so I can better understand the problem being fixed, I guess you can have > > > > two consecutive pfns with non-consecutive associated struct page if you have two > > > > adjacent memory sections spanning the same physical memory region, is that > > > > correct? > > > > > > Exactly. Essentially on SPARSEMEM without SPARSEMEM_VMEMMAP it is not > > > guaranteed that > > > > > > pfn_to_page(pfn + 1) == pfn_to_page(pfn) + 1 > > > > > > when we cross memory section boundaries. > > > > > > It can be the case for early boot memory if we allocated consecutive areas > > > from memblock when allocating the memmap (struct pages) per memory section, > > > but it's not guaranteed. > > > > Thank you for the explanation, but I'm a bit confused by the last paragraph. I > > think what you're saying is that we can also have the reverse problem, where > > consecutive struct page * represent non-consecutive pfns, because memmap > > allocations happened to return consecutive virtual addresses, is that right? > > Exactly, that's something we have to deal with elsewhere [1]. For this code, > it's not a problem because we always allocate a contiguous PFN range. > > > > > If that's correct, I don't think that's the case for CMA, which deals out > > contiguous physical memory. Or were you just trying to explain the other side of > > the problem, and I'm just overthinking it? > > The latter :) Ok, sorry for the noise then, and thank you for educating me. Alex