linux-kernel - Re: [PATCH v2 0/5] KVM: mm: count KVM page table pages in pagetable stats

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Message-ID: <YkyOJqTeGRUjtuX1@google.com>
Date:   Tue, 5 Apr 2022 18:44:54 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, mizhang@...gle.com,
        David Matlack <dmatlack@...gle.com>, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 0/5] KVM: mm: count KVM page table pages in pagetable
 stats

On Mon, Apr 04, 2022, 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 for its page tables is not accounted in
> the pagetable stats. This patch series accounts the memory pages used by
> KVM for page tables in those stats.

It's still not obvious to me that piggybacking NR_PAGETABLE is desirable, probably
because I am quite clueless as to how these stats are used on the backend.  E.g.
why not have a NR_SECONDARY_PAGETABLE entry to track pages used for secondary MMU
page tables?