netdev - Re: [PATCH resend mm,net-next 1/3] mm: Refactor insert

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Date:   Thu, 13 Feb 2020 08:55:28 -0800
From:   Arjun Roy <arjunroy@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Arjun Roy <arjunroy.kdev@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org, linux-mm@...ck.org,
        Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH resend mm,net-next 1/3] mm: Refactor insert_page to
 prepare for batched-lock insert.

The addition of page_has_type() looks good to me, thanks!

-Arjun


On Wed, Feb 12, 2020 at 6:41 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Mon, 27 Jan 2020 18:59:56 -0800 Arjun Roy <arjunroy.kdev@...il.com> wrote:
>
> > Add helper methods for vm_insert_page()/insert_page() to prepare for
> > vm_insert_pages(), which batch-inserts pages to reduce spinlock
> > operations when inserting multiple consecutive pages into the user
> > page table.
> >
> > The intention of this patch-set is to reduce atomic ops for
> > tcp zerocopy receives, which normally hits the same spinlock multiple
> > times consecutively.
>
> I tweaked this a bit for the addition of page_has_type() to
> insert_page().  Please check.
>
>
>
> From: Arjun Roy <arjunroy.kdev@...il.com>
> Subject: mm: Refactor insert_page to prepare for batched-lock insert.
>
> From: Arjun Roy <arjunroy@...gle.com>
>
> Add helper methods for vm_insert_page()/insert_page() to prepare for
> vm_insert_pages(), which batch-inserts pages to reduce spinlock
> operations when inserting multiple consecutive pages into the user
> page table.
>
> The intention of this patch-set is to reduce atomic ops for
> tcp zerocopy receives, which normally hits the same spinlock multiple
> times consecutively.
>
> Link: http://lkml.kernel.org/r/20200128025958.43490-1-arjunroy.kdev@gmail.com
> Signed-off-by: Arjun Roy <arjunroy@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
>
>  mm/memory.c |   39 ++++++++++++++++++++++++---------------
>  1 file changed, 24 insertions(+), 15 deletions(-)
>
> --- a/mm/memory.c~mm-refactor-insert_page-to-prepare-for-batched-lock-insert
> +++ a/mm/memory.c
> @@ -1430,6 +1430,27 @@ pte_t *__get_locked_pte(struct mm_struct
>         return pte_alloc_map_lock(mm, pmd, addr, ptl);
>  }
>
> +static int validate_page_before_insert(struct page *page)
> +{
> +       if (PageAnon(page) || PageSlab(page) || page_has_type(page))
> +               return -EINVAL;
> +       flush_dcache_page(page);
> +       return 0;
> +}
> +
> +static int insert_page_into_pte_locked(struct mm_struct *mm, pte_t *pte,
> +                       unsigned long addr, struct page *page, pgprot_t prot)
> +{
> +       if (!pte_none(*pte))
> +               return -EBUSY;
> +       /* Ok, finally just insert the thing.. */
> +       get_page(page);
> +       inc_mm_counter_fast(mm, mm_counter_file(page));
> +       page_add_file_rmap(page, false);
> +       set_pte_at(mm, addr, pte, mk_pte(page, prot));
> +       return 0;
> +}
> +
>  /*
>   * This is the old fallback for page remapping.
>   *
> @@ -1445,26 +1466,14 @@ static int insert_page(struct vm_area_st
>         pte_t *pte;
>         spinlock_t *ptl;
>
> -       retval = -EINVAL;
> -       if (PageAnon(page) || PageSlab(page) || page_has_type(page))
> +       retval = validate_page_before_insert(page);
> +       if (retval)
>                 goto out;
>         retval = -ENOMEM;
> -       flush_dcache_page(page);
>         pte = get_locked_pte(mm, addr, &ptl);
>         if (!pte)
>                 goto out;
> -       retval = -EBUSY;
> -       if (!pte_none(*pte))
> -               goto out_unlock;
> -
> -       /* Ok, finally just insert the thing.. */
> -       get_page(page);
> -       inc_mm_counter_fast(mm, mm_counter_file(page));
> -       page_add_file_rmap(page, false);
> -       set_pte_at(mm, addr, pte, mk_pte(page, prot));
> -
> -       retval = 0;
> -out_unlock:
> +       retval = insert_page_into_pte_locked(mm, pte, addr, page, prot);
>         pte_unmap_unlock(pte, ptl);
>  out:
>         return retval;
> _
>