linux-kernel - Re: [PATCH mm-unstable 3/4] mm: multi-gen LRU: add helpers in page table walks

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Date:   Thu, 1 Jun 2023 16:02:26 +0800
From:   Yuanchu Xie <yuanchu@...gle.com>
To:     "T.J. Alumbaugh" <talumbau@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Yu Zhao <yuzhao@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-mm@...gle.com
Subject: Re: [PATCH mm-unstable 3/4] mm: multi-gen LRU: add helpers in page
 table walks

On Mon, May 22, 2023 at 7:21 PM T.J. Alumbaugh <talumbau@...gle.com> wrote:
>
> Add helpers to page table walking code:
>  - Clarifies intent via name "should_walk_mmu" and "should_clear_pmd_young"
I wonder if these should be called "can_walk_mmu" and
"can_clear_pmd_young", but that's rather minor.

>  - Avoids repeating same logic in two places
>
> Signed-off-by: T.J. Alumbaugh <talumbau@...gle.com>
> ---
>  mm/vmscan.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index e088db138f5f..ad0f589d32e6 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3234,6 +3234,16 @@ DEFINE_STATIC_KEY_ARRAY_FALSE(lru_gen_caps, NR_LRU_GEN_CAPS);
>  #define get_cap(cap)   static_branch_unlikely(&lru_gen_caps[cap])
>  #endif
>
> +static bool should_walk_mmu(void)
> +{
> +       return arch_has_hw_pte_young() && get_cap(LRU_GEN_MM_WALK);
> +}
> +
> +static bool should_clear_pmd_young(void)
> +{
> +       return arch_has_hw_nonleaf_pmd_young() && get_cap(LRU_GEN_NONLEAF_YOUNG);
> +}
> +
>  /******************************************************************************
>   *                          shorthand helpers
>   ******************************************************************************/
> @@ -4098,7 +4108,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
>                         goto next;
>
>                 if (!pmd_trans_huge(pmd[i])) {
> -                       if (arch_has_hw_nonleaf_pmd_young() && get_cap(LRU_GEN_NONLEAF_YOUNG))
> +                       if (should_clear_pmd_young())
>                                 pmdp_test_and_clear_young(vma, addr, pmd + i);
>                         goto next;
>                 }
> @@ -4191,7 +4201,7 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
>  #endif
>                 walk->mm_stats[MM_NONLEAF_TOTAL]++;
>
> -               if (arch_has_hw_nonleaf_pmd_young() && get_cap(LRU_GEN_NONLEAF_YOUNG)) {
> +               if (should_clear_pmd_young()) {
>                         if (!pmd_young(val))
>                                 continue;
>
> @@ -4493,7 +4503,7 @@ static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long max_seq,
>          * handful of PTEs. Spreading the work out over a period of time usually
>          * is less efficient, but it avoids bursty page faults.
>          */
> -       if (!arch_has_hw_pte_young() || !get_cap(LRU_GEN_MM_WALK)) {
> +       if (!should_walk_mmu()) {
>                 success = iterate_mm_list_nowalk(lruvec, max_seq);
>                 goto done;
>         }
> @@ -5730,10 +5740,10 @@ static ssize_t enabled_show(struct kobject *kobj, struct kobj_attribute *attr, c
>         if (get_cap(LRU_GEN_CORE))
>                 caps |= BIT(LRU_GEN_CORE);
>
> -       if (arch_has_hw_pte_young() && get_cap(LRU_GEN_MM_WALK))
> +       if (should_walk_mmu())
>                 caps |= BIT(LRU_GEN_MM_WALK);
>
> -       if (arch_has_hw_nonleaf_pmd_young() && get_cap(LRU_GEN_NONLEAF_YOUNG))
> +       if (should_clear_pmd_young())
>                 caps |= BIT(LRU_GEN_NONLEAF_YOUNG);
>
>         return sysfs_emit(buf, "0x%04x\n", caps);
> --
> 2.40.1.698.g37aff9b760-goog
>
Other than that,
Reviewed-by: Yuanchu Xie <yuanchu@...gle.com>