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Date:   Mon, 13 Jun 2022 11:28:28 -0700
From:   Mike kravetz <mike.kravetz@oracle.com>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     david@redhat.com, akpm@linux-foundation.org, corbet@lwn.net,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org
Subject: Re: [PATCH 2/6] mm: hugetlb_vmemmap: optimize vmemmap_optimize_mode
 handling
Message-ID: <YqeBzNYrgFGqtfaj@monkey>
References: <20220613063512.17540-1-songmuchun@bytedance.com>
 <20220613063512.17540-3-songmuchun@bytedance.com>
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On Mon, Jun 13, 2022 at 02:35:08PM +0800”, Muchun Song wrote:
> We hold an another reference to hugetlb_optimize_vmemmap_key when
> making vmemmap_optimize_mode on, because we use static_key to tell
> memory_hotplug that memory_hotplug.memmap_on_memory should be
> overridden.  However, this rule has gone when we have introduced
> SECTION_CANNOT_OPTIMIZE_VMEMMAP.  Therefore, we could simplify
> vmemmap_optimize_mode handling by not holding an another reference
> to hugetlb_optimize_vmemmap_key.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  include/linux/page-flags.h |  6 ++---
>  mm/hugetlb_vmemmap.c       | 65 +++++-----------------------------------------
>  2 files changed, 9 insertions(+), 62 deletions(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index b8b992cb201c..da7ccc3b16ad 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -200,8 +200,7 @@ enum pageflags {
>  #ifndef __GENERATING_BOUNDS_H
>  
>  #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> -DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
> -			 hugetlb_optimize_vmemmap_key);
> +DECLARE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
>  
>  /*
>   * If the feature of optimizing vmemmap pages associated with each HugeTLB
> @@ -221,8 +220,7 @@ DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
>   */
>  static __always_inline const struct page *page_fixed_fake_head(const struct page *page)
>  {
> -	if (!static_branch_maybe(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
> -				 &hugetlb_optimize_vmemmap_key))
> +	if (!static_branch_unlikely(&hugetlb_optimize_vmemmap_key))
>  		return page;

This also means that we not incur the extra page_fixed_fake_head checks
if there are no vmemmap optinmized hugetlb pages.  Nice!

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz