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 43745C43334 for ; Wed, 29 Jun 2022 10:29:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233342AbiF2K36 (ORCPT ); Wed, 29 Jun 2022 06:29:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39986 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230315AbiF2K34 (ORCPT ); Wed, 29 Jun 2022 06:29:56 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C14492621; Wed, 29 Jun 2022 03:29:55 -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 74AADB8227D; Wed, 29 Jun 2022 10:29:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E71AC34114; Wed, 29 Jun 2022 10:29:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1656498593; bh=6t4Qww5gQL2dPbX3lWrf1eT1qNVh0NYZw5CcQii/4dM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=nvDqmPQ6eBKyTUKtozYUlsMzXrump4i5EVvFFIkTkP4/jSoJzd2ro8PLYBFW362Mj 09dLnzVJ1RBJIqoRvakCpzH7jvr2a3OYquFglJCocMOwPRxfXkZIO4Jj7d4RAWO1vY LDKGc4+cPyW1yZ159pyhUr3Gxa+30RByCwS+FI8+9+n+xUuM1z5uAQ2eAJqgPaXuFM uyQ175SDqmHxSNcDppdDbIFGv20UX1/gQbmiLW0m4f92bY0OOCprHBsNzQgLjQg3+x LoqmwaPmDGkJLxdhgkeXsgvBwGSJJeJLo+yQupwk03grJMn5nSqh302TLrLAqd/ihr UfpW+K4y5g1pw== Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1o6UxC-0042RV-W7; Wed, 29 Jun 2022 11:29:51 +0100 Date: Wed, 29 Jun 2022 11:29:50 +0100 Message-ID: <8735fn3gpt.wl-maz@kernel.org> From: Marc Zyngier To: Yosry Ahmed Cc: Tejun Heo , Johannes Weiner , Zefan Li , James Morse , Alexandru Elisei , Suzuki K Poulose , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Andrew Morton , 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. In-Reply-To: <20220628220938.3657876-2-yosryahmed@google.com> References: <20220628220938.3657876-1-yosryahmed@google.com> <20220628220938.3657876-2-yosryahmed@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: yosryahmed@google.com, tj@kernel.org, hannes@cmpxchg.org, lizefan.x@bytedance.com, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, akpm@linux-foundation.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeelb@google.com, oupton@google.com, Huang@google.com, shaoqin.huang@intel.com, 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 X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 28 Jun 2022 23:09:35 +0100, 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. > > Signed-off-by: Yosry Ahmed > Acked-by: Shakeel Butt Acked-by: Marc Zyngier M. -- Without deviation from the norm, progress is not possible.