linux-kernel - Re: [PATCH v4 1/4] mm: add NR_SECONDARY_PAGETABLE to count secondary page table uses.

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Message-ID: <CALvZod4w88YDCpageGPDZfCcFwi2C4YfSsavd-Svixovvx5n_A@mail.gmail.com>
Date:   Thu, 12 May 2022 13:36:44 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>, Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Zefan Li <lizefan.x@...edance.com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Oliver Upton <oupton@...gle.com>,
        Cgroups <cgroups@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v4 1/4] mm: add NR_SECONDARY_PAGETABLE to count secondary
 page table uses.

On Mon, May 9, 2022 at 9:38 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
[...]
> > >
> > > What do you plan to do for IOMMU page tables? After all, they serve
> > > the exact same purpose, and I'd expect these to be handled the same
> > > way (i.e. why is this KVM specific?).
> >
> > The reason this was named NR_SECONDARY_PAGTABLE instead of
> > NR_KVM_PAGETABLE is exactly that. To leave room to incrementally
> > account other types of secondary page tables to this stat. It is just
> > that we are currently interested in the KVM MMU usage.
> >
>
>
> Any thoughts on this? Do you think MEMCG_SECONDARY_PAGETABLE would be
> more appropriate here?

I think NR_SECONDARY_PAGTABLE is good. Later it can include pagetables
from other subsystems. The only nit (which you can ignore) I have is
the very long memcg stat and vmstat names. Other than that the patch
looks good to me.