linux-kernel - Re: [PATCH v5 1/4] mm: add NR_SECONDARY_PAGETABLE to count secondary page table uses.

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Message-ID: <CAJD7tkaMYhG7_AQgn6fLGFVuSB4wDpY_GzcvSS99tSzTUKFkTw@mail.gmail.com>
Date:   Mon, 27 Jun 2022 09:23:55 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        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>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        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 v5 1/4] mm: add NR_SECONDARY_PAGETABLE to count secondary
 page table uses.

On Mon, Jun 27, 2022 at 9:07 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Mon, Jun 06, 2022, Yosry Ahmed wrote:
> > Add NR_SECONDARY_PAGETABLE stat to count secondary page table uses, e.g.
> > KVM mmu. This provides more insights on the kernel memory used
> > by a workload.
>
> Please provide more justification for NR_SECONDARY_PAGETABLE in the changelog.
> Specially, answer the questions that were asked in the previous version:
>
>   1. Why not piggyback NR_PAGETABLE?
>   2. Why a "generic" NR_SECONDARY_PAGETABLE instead of NR_VIRT_PAGETABLE?
>
> It doesn't have to be super long, but provide enough info so that reviewers and
> future readers don't need to go spelunking to understand the motivation for the
> new counter type.

I added such justification in the cover letter, is it better to
include it here alternatively?
or do you think the description in the cover letter is lacking?

>
> And it's probably worth an explicit Link to Marc's question that prompted the long
> discussion in the previous version, that way if someone does want the gory details
> they have a link readily available.
>
> Link: https://lore.kernel.org/all/87ilqoi77b.wl-maz@kernel.org

I will include the link in the next version.
Thanks!