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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BE8B6C32771 for ; Wed, 17 Aug 2022 17:24:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240301AbiHQRYP (ORCPT ); Wed, 17 Aug 2022 13:24:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43816 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237745AbiHQRYO (ORCPT ); Wed, 17 Aug 2022 13:24:14 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DC3F4A0250; Wed, 17 Aug 2022 10:24:12 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 920A6B81E81; Wed, 17 Aug 2022 17:24:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 684EFC433B5; Wed, 17 Aug 2022 17:24:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1660757050; bh=h7rloNmTPwUDXGSYX5u3jVl/NrdFIyTwfIZuYDpyc+s=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=SCu1HHR6yDn0wowMIHnbsEbhjw3fO1TLcBcRSyKUXhWF/dl/GDPzQvg9LYQvU2YWP jBgUTXdC1VHSy6asKtLxxa4w4uLsVNSoZ57fahkuaNnkeeBRwR6GmBa/lfF6BHegwJ BaN4hOiavyPxE2PiZVXnb/b8vqfCGE1FVzDXR9rk= Date: Wed, 17 Aug 2022 10:24:08 -0700 From: Andrew Morton To: Yosry Ahmed Cc: Tejun Heo , Johannes Weiner , Zefan Li , Marc Zyngier , James Morse , Alexandru Elisei , Suzuki K Poulose , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Michal Hocko , Roman Gushchin , Shakeel Butt , Oliver Upton , Huang@google.com, Shaoqin , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v6 1/4] mm: add NR_SECONDARY_PAGETABLE to count secondary page table uses. Message-Id: <20220817102408.7b048f198a736f053ced2862@linux-foundation.org> In-Reply-To: <20220628220938.3657876-2-yosryahmed@google.com> References: <20220628220938.3657876-1-yosryahmed@google.com> <20220628220938.3657876-2-yosryahmed@google.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, 28 Jun 2022 22:09:35 +0000 Yosry Ahmed wrote: > We keep track of several kernel memory stats (total kernel memory, page > tables, stack, vmalloc, etc) on multiple levels (global, per-node, > per-memcg, etc). These stats give insights to users to how much memory > is used by the kernel and for what purposes. > > Currently, memory used by kvm mmu is not accounted in any of those > kernel memory stats. This patch series accounts the memory pages > used by KVM for page tables in those stats in a new > NR_SECONDARY_PAGETABLE stat. This stat can be later extended to account > for other types of secondary pages tables (e.g. iommu page tables). > > KVM has a decent number of large allocations that aren't for page > tables, but for most of them, the number/size of those allocations > scales linearly with either the number of vCPUs or the amount of memory > assigned to the VM. KVM's secondary page table allocations do not scale > linearly, especially when nested virtualization is in use. > > >From a KVM perspective, NR_SECONDARY_PAGETABLE will scale with KVM's > per-VM pages_{4k,2m,1g} stats unless the guest is doing something > bizarre (e.g. accessing only 4kb chunks of 2mb pages so that KVM is > forced to allocate a large number of page tables even though the guest > isn't accessing that much memory). However, someone would need to either > understand how KVM works to make that connection, or know (or be told) to > go look at KVM's stats if they're running VMs to better decipher the stats. > > Furthermore, having NR_PAGETABLE side-by-side with NR_SECONDARY_PAGETABLE > is informative. For example, when backing a VM with THP vs. HugeTLB, > NR_SECONDARY_PAGETABLE is roughly the same, but NR_PAGETABLE is an order > of magnitude higher with THP. So having this stat will at the very least > prove to be useful for understanding tradeoffs between VM backing types, > and likely even steer folks towards potential optimizations. > > The original discussion with more details about the rationale: > https://lore.kernel.org/all/87ilqoi77b.wl-maz@kernel.org > > This stat will be used by subsequent patches to count KVM mmu > memory usage. Nits and triviata: > --- a/Documentation/filesystems/proc.rst > +++ b/Documentation/filesystems/proc.rst > @@ -977,6 +977,7 @@ Example output. You may not have all of these fields. > SUnreclaim: 142336 kB > KernelStack: 11168 kB > PageTables: 20540 kB > + SecPageTables: 0 kB > NFS_Unstable: 0 kB > Bounce: 0 kB > WritebackTmp: 0 kB > @@ -1085,6 +1086,9 @@ KernelStack > Memory consumed by the kernel stacks of all tasks > PageTables > Memory consumed by userspace page tables > +SecPageTables > + Memory consumed by secondary page tables, this currently > + currently includes KVM mmu allocations on x86 and arm64. Something happened to the whitespace there. > + "Node %d SecPageTables: %8lu kB\n" > ... > + nid, K(node_page_state(pgdat, NR_SECONDARY_PAGETABLE)), The use of "sec" in the user-facing changes and "secondary" in the programmer-facing changes is irksome. Can we be consistent? I'd prefer "secondary" throughout.