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 3D1E2C021A0 for ; Thu, 13 Feb 2025 16:04:50 +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=4N80hDSqq8aH8PAPx57HquTznMqgSlfxParpspmHijM=; b=0SuLaMXHqXF06G/096xSWR5JCg AwfGp3BRqsfG0MgMo3goqv0mnjAbPV9IVVAwg923rL+D+NAvo9ih2gdonlP4cbGx55YD3NLlwOg7u QENEMy61rz9guqHle8KSjwXrYKwPYaD7WqMbO62Yt0/q+3HRQxfRQM9DzSjtOmzxorc10g4dBG96o pes57/l8CzP2tof4Ypid9kWh5jEPf7G3jsAFt4Uuv0GfTgodsLC23Jj47SOPDf0P9NbhtsBzO75zM pNhX9rWnJ/xRWJs2nP8bObfVOAIDz5lBaT/NBbd3DHNrHTchRbVxg/dVk7WDEy+pXSkpl2J8xbOT3 UyVhw2cQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tibhb-0000000Bfui-32Ms; Thu, 13 Feb 2025 16:04:35 +0000 Received: from nyc.source.kernel.org ([147.75.193.91]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tibSj-0000000BcMB-3Orf for linux-arm-kernel@lists.infradead.org; Thu, 13 Feb 2025 15:49:14 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id AC64DA42704; Thu, 13 Feb 2025 15:47:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D9BFCC4CED1; Thu, 13 Feb 2025 15:49:09 +0000 (UTC) Date: Thu, 13 Feb 2025 15:49:07 +0000 From: Catalin Marinas To: David Hildenbrand Cc: Zhenhua Huang , anshuman.khandual@arm.com, will@kernel.org, ardb@kernel.org, ryan.roberts@arm.com, mark.rutland@arm.com, joey.gouly@arm.com, dave.hansen@linux.intel.com, akpm@linux-foundation.org, chenfeiyang@loongson.cn, chenhuacai@kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, quic_tingweiz@quicinc.com, stable@vger.kernel.org Subject: Re: [PATCH v6] arm64: mm: Populate vmemmap/linear at the page level for hotplugged sections Message-ID: References: <20250213075703.1270713-1-quic_zhenhuah@quicinc.com> <9bc91fe3-c590-48e2-b29f-736d0b056c34@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9bc91fe3-c590-48e2-b29f-736d0b056c34@redhat.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250213_074913_912411_9B41E3CB X-CRM114-Status: GOOD ( 20.33 ) 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 On Thu, Feb 13, 2025 at 01:59:25PM +0100, David Hildenbrand wrote: > On 13.02.25 08:57, Zhenhua Huang wrote: > > On the arm64 platform with 4K base page config, SECTION_SIZE_BITS is set > > to 27, making one section 128M. The related page struct which vmemmap > > points to is 2M then. > > Commit c1cc1552616d ("arm64: MMU initialisation") optimizes the > > vmemmap to populate at the PMD section level which was suitable > > initially since hot plug granule is always one section(128M). However, > > commit ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > > introduced a 2M(SUBSECTION_SIZE) hot plug granule, which disrupted the > > existing arm64 assumptions. > > > > Considering the vmemmap_free -> unmap_hotplug_pmd_range path, when > > pmd_sect() is true, the entire PMD section is cleared, even if there is > > other effective subsection. For example page_struct_map1 and > > page_strcut_map2 are part of a single PMD entry and they are hot-added > > sequentially. Then page_struct_map1 is removed, vmemmap_free() will clear > > the entire PMD entry freeing the struct page map for the whole section, > > even though page_struct_map2 is still active. Similar problem exists > > with linear mapping as well, for 16K base page(PMD size = 32M) or 64K > > base page(PMD = 512M), their block mappings exceed SUBSECTION_SIZE. > > Tearing down the entire PMD mapping too will leave other subsections > > unmapped in the linear mapping. > > > > To address the issue, we need to prevent PMD/PUD/CONT mappings for both > > linear and vmemmap for non-boot sections if corresponding size on the > > given base page exceeds SUBSECTION_SIZE(2MB now). > > > > Cc: # v5.4+ > > Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > > Reviewed-by: Catalin Marinas > > Signed-off-by: Zhenhua Huang > > Just so I understand correctly: for ordinary memory-sections-size hotplug > (NVDIMM, virtio-mem), we still get a large mapping where possible? Up to 2MB blocks only since that's the SUBSECTION_SIZE value. The vmemmap mapping is also limited to PAGE_SIZE mappings (we could use contiguous mappings for vmemmap but it's not wired up; I don't think it's worth the hassle). -- Catalin