linux-kernel - Re: [PATCH v2 4/5] mm/huge_memory.c: remove unnecessary tlb_remove_page

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Message-ID: <CAHbLzkr2o1xjY4sHFPMv=vZm9Dysu+YJkaiab9AtJd9FcZJ5sg@mail.gmail.com>
Date:   Thu, 29 Apr 2021 10:55:12 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, Zi Yan <ziy@...dia.com>,
        william.kucharski@...cle.com, Matthew Wilcox <willy@...radead.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        aneesh.kumar@...ux.ibm.com, Ralph Campbell <rcampbell@...dia.com>,
        Song Liu <songliubraving@...com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Minchan Kim <minchan@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2 4/5] mm/huge_memory.c: remove unnecessary
 tlb_remove_page_size() for huge zero pmd

On Thu, Apr 29, 2021 at 6:27 AM Miaohe Lin <linmiaohe@...wei.com> wrote:
>
> Commit aa88b68c3b1d ("thp: keep huge zero page pinned until tlb flush")
> introduced tlb_remove_page() for huge zero page to keep it pinned until
> flush is complete and prevents the page from being split under us. But
> huge zero page is kept pinned until all relevant mm_users reach zero since
> the commit 6fcb52a56ff6 ("thp: reduce usage of huge zero page's atomic
> counter"). So tlb_remove_page_size() for huge zero pmd is unnecessary now.

By reading the git history, it seems the lifecycle of huge zero page
is bound to process instead of page table due to the latter commit.
The patch looks correct to me. Reviewed-by: Yang Shi
<shy828301@...il.com>

>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/huge_memory.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index e24a96de2e37..af30338ac49c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1680,12 +1680,9 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>                 if (arch_needs_pgtable_deposit())
>                         zap_deposited_table(tlb->mm, pmd);
>                 spin_unlock(ptl);
> -               if (is_huge_zero_pmd(orig_pmd))
> -                       tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
>         } else if (is_huge_zero_pmd(orig_pmd)) {
>                 zap_deposited_table(tlb->mm, pmd);
>                 spin_unlock(ptl);
> -               tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
>         } else {
>                 struct page *page = NULL;
>                 int flush_needed = 1;
> --
> 2.23.0
>
>