linux-kernel - Re: [Patch v2 0/2] NUMA aware page table allocation

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Date:   Thu, 8 Dec 2022 16:21:15 -0800
From:   David Matlack <dmatlack@...gle.com>
To:     Vipin Sharma <vipinsh@...gle.com>
Cc:     bgardon@...gle.com, seanjc@...gle.com, pbonzini@...hat.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch v2 0/2] NUMA aware page table allocation

On Thu, Dec 01, 2022 at 11:57:16AM -0800, Vipin Sharma wrote:
> Hi,
> 
> This series improves page table accesses by allocating page tables on
> the same NUMA node where underlying physical page is present.
> 
> Currently page tables are allocated during page faults and page splits.
> In both instances page table location will depend on the current thread
> mempolicy. This can create suboptimal placement of page tables on NUMA
> node, for example, thread doing eager page split is on different NUMA
> node compared to page it is splitting.
> 
> Reviewers please provide suggestion to the following:
> 
> 1. Module parameter is true by default, which means this feature will
>    be enabled by default. Is this okay or should I set it to false?
> 
> 2. I haven't reduced KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE considering that
>    it might not be too much of an impact as only online nodes are filled
>    during topup phase and in many cases some of these nodes will never
>    be refilled again.  Please let me know if you want this to be
>    reduced.
> 
> 3. I have tried to keep everything in x86/mmu except for some changes in
>    virt/kvm/kvm_main.c. I used __weak function so that only x86/mmu will
>    see the change, other arch nothing will change. I hope this is the
>    right approach.
> 
> 4. I am not sure what is the right way to split patch 2. If you think
>    this is too big for a patch please let me know what would you prefer.

I agree it's too big. The split_shadow_page_cache changes can easily be
split into a separate commit.