linux-kernel - Re: [Patch v4 03/18] KVM: x86/mmu: Track count of pages in KVM MMU page caches globally

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Date:   Thu, 9 Mar 2023 15:53:43 -0800
From:   David Matlack <dmatlack@...gle.com>
To:     Vipin Sharma <vipinsh@...gle.com>
Cc:     seanjc@...gle.com, pbonzini@...hat.com, bgardon@...gle.com,
        jmattson@...gle.com, mizhang@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Patch v4 03/18] KVM: x86/mmu: Track count of pages in KVM MMU
 page caches globally

On Mon, Mar 06, 2023 at 02:41:12PM -0800, Vipin Sharma wrote:
> Create a global counter for total number of pages available
> in MMU page caches across all VMs. Add mmu_shadow_page_cache
> pages to this counter.

I think I prefer counting the objects on-demand in mmu_shrink_count(),
instead of keeping track of the count. Keeping track of the count adds
complexity to the topup/alloc paths for the sole benefit of the
shrinker. I'd rather contain that complexity to the shrinker code unless
there is a compelling reason to optimize mmu_shrink_count().

IIRC we discussed this at one point. Was there a reason to take this
approach that I'm just forgetting?