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References: <20220404234154.1251388-1-yosryahmed@google.com> <YkyOJqTeGRUjtuX1@google.com>
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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Tue, 5 Apr 2022 11:50:09 -0700
Message-ID: <CAJD7tkYqSMk5UO5A46sR1cOviDeww0=JsR6QRMO9ZRF_7NLXBA@mail.gmail.com>
Subject: Re: [PATCH v2 0/5] KVM: mm: count KVM page table pages in pagetable stats
To:     Sean Christopherson <seanjc@google.com>
Cc:     Huacai Chen <chenhuacai@kernel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
        Anup Patel <anup@brainfault.org>,
        Atish Patra <atishp@atishpatra.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, mizhang@google.com,
        David Matlack <dmatlack@google.com>, kvm@vger.kernel.org,
        kvm-riscv@lists.infradead.org, linux-mips@vger.kernel.org,
        Linux-MM <linux-mm@kvack.org>,
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        Shakeel Butt <shakeelb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>
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+Johannes Weiner  +Michal Hocko  +Roman Gushchin

On Tue, Apr 5, 2022 at 11:45 AM Sean Christopherson <seanjc@google.com> wrote:
>
> 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?

We can add NR_SECONDARY_PAGETABLE or even NR_KVM_PAGETABLE, but I am
not sure whether this separation is desired on the MM side. Let's see
what MM folks think about this.