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

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Date:   Tue, 5 Apr 2022 11:50:09 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Sean Christopherson <seanjc@...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 <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: [PATCH v2 0/5] KVM: mm: count KVM page table pages in pagetable stats

+Johannes Weiner  +Michal Hocko  +Roman Gushchin

On Tue, Apr 5, 2022 at 11:45 AM Sean Christopherson <seanjc@...gle.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.