linux-kernel - Re: [PATCH 5/5] KVM: selftests: access_tracking_perf

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Message-ID: <CADrL8HXEb0r8sRie_q48ry8r30LpBZqAs4a1iN8N9BZ09FZzUw@mail.gmail.com>
Date: Thu, 27 Mar 2025 11:26:57 -0700
From: James Houghton <jthoughton@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org
Cc: Maxim Levitsky <mlevitsk@...hat.com>, Axel Rasmussen <axelrasmussen@...gle.com>, 
	Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, mkoutny@...e.com, 
	Yu Zhao <yuzhao@...gle.com>, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] KVM: selftests: access_tracking_perf_test: Use MGLRU
 for access tracking

On Wed, Mar 26, 2025 at 6:25 PM James Houghton <jthoughton@...gle.com> wrote:
> diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> index 0e594883ec13e..1c8e43e18e4c6 100644
> --- a/tools/testing/selftests/kvm/access_tracking_perf_test.c
> +++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> @@ -318,6 +415,15 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>         pr_info("\n");
>         access_memory(vm, nr_vcpus, ACCESS_WRITE, "Populating memory");
>
> +       if (use_lru_gen) {
> +               struct memcg_stats stats;
> +
> +               /* Do an initial page table scan */

This comment is wrong, sorry. I'll just drop it.

I initially had a lru_gen_do_aging() here to verify that everything
was tracked in the lru_gen debugfs, but everything is already tracked
anyway. Doing an aging pass here means that the "control" write after
this is writing to idle memory, so it ceases to be a control.

> +               lru_gen_read_memcg_stats(&stats, TEST_MEMCG_NAME);
> +               TEST_ASSERT(lru_gen_sum_memcg_stats(&stats) >= total_pages,
> +                           "Not all pages accounted for. Was the memcg set up correctly?");
> +       }
> +
>         /* As a control, read and write to the populated memory first. */
>         access_memory(vm, nr_vcpus, ACCESS_WRITE, "Writing to populated memory");
>         access_memory(vm, nr_vcpus, ACCESS_READ, "Reading from populated memory");