linux-kernel - Re: [PATCH 07/12] KVM: X86/MMU: Remove the useless struct mmu_page

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Message-ID: <CAJhGHyB=-bGrguLKtTh+EAr5zr--H97HUgR3WP=JTovQLkoevQ@mail.gmail.com>
Date:   Thu, 21 Jul 2022 17:43:20 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR MIPS (KVM/mips)" 
        <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Lai Jiangshan <jiangshan.ljs@...group.com>
Subject: Re: [PATCH 07/12] KVM: X86/MMU: Remove the useless struct mmu_page_path

On Wed, Jul 20, 2022 at 4:15 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Nit, s/useless/now-unused, or "no longer used".  I associate "useless" in shortlogs
> as "this <xyz> is pointless and always has been pointless", whereas "now-unused"
> is likely to be interpreted as "remove <xyz> as it's no longer used after recent
> changes".
>
> Alternatively, can this patch be squashed with the patch that removes
> mmu_pages_clear_parents()?  Yeah, it'll be a (much?) larger patch, but leaving
> dead code behind is arguably worse.

Defined by the C-language and the machine, struct mmu_page_path is used
in for_each_sp() and the data is set and updated every iteration.

It is not really dead code.

Defined by the sematic that we want, gathering unsync pages,
we don't need struct mmu_page_path, since the struct is not used
by "someone reading it".

>
> On Sun, Jun 05, 2022, Lai Jiangshan wrote:
> > From: Lai Jiangshan <jiangshan.ljs@...group.com>
> >
> > struct mmu_page_path is set and updated but never used since
> > mmu_pages_clear_parents() is removed.
> >
> > Remove it.
> >
> > Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
> > ---