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From:   Alistair Popple <apopple@nvidia.com>
To:     Hugh Dickins <hughd@google.com>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Christoph Hellwig <hch@lst.de>, Yang Shi <shy828301@gmail.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Shakeel Butt <shakeelb@google.com>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH 1/4] mm/rmap: fix comments left over from recent changes
Date:   Thu, 8 Jul 2021 09:34:06 +1000
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On Thursday, 8 July 2021 6:06:17 AM AEST Hugh Dickins wrote:
> Parallel developments in mm/rmap.c have left behind some out-of-date
> comments: try_to_migrate_one() also accepts TTU_SYNC (already commented
> in try_to_migrate() itself), and try_to_migrate() returns nothing at all.
> 
> TTU_SPLIT_FREEZE has just been deleted, so reword the comment about it in
> mm/huge_memory.c; and TTU_IGNORE_ACCESS was removed in 5.11, so delete
> the "recently referenced" comment from try_to_unmap_one() (once upon a
> time the comment was near the removed codeblock, but they drifted apart).
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>

Reviewed-by: Alistair Popple <apopple@nvidia.com>

> ---
>  mm/huge_memory.c | 2 +-
>  mm/rmap.c        | 7 +------
>  2 files changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 8b731d53e9f4..afff3ac87067 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2331,7 +2331,7 @@ static void remap_page(struct page *page, unsigned int nr)
>  {
>  	int i;
>  
> -	/* If TTU_SPLIT_FREEZE is ever extended to file, remove this check */
> +	/* If unmap_page() uses try_to_migrate() on file, remove this check */
>  	if (!PageAnon(page))
>  		return;
>  	if (PageTransHuge(page)) {
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 37c24672125c..746013e282c3 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1439,8 +1439,6 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>  	while (page_vma_mapped_walk(&pvmw)) {
>  		/*
>  		 * If the page is mlock()d, we cannot swap it out.
> -		 * If it's recently referenced (perhaps page_referenced
> -		 * skipped over this mm) then we should reactivate it.
>  		 */
>  		if (!(flags & TTU_IGNORE_MLOCK)) {
>  			if (vma->vm_flags & VM_LOCKED) {
> @@ -1687,8 +1685,7 @@ void try_to_unmap(struct page *page, enum ttu_flags flags)
>   * @arg: enum ttu_flags will be passed to this argument.
>   *
>   * If TTU_SPLIT_HUGE_PMD is specified any PMD mappings will be split into PTEs
> - * containing migration entries. This and TTU_RMAP_LOCKED are the only supported
> - * flags.
> + * containing migration entries.
>   */
>  static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
>  		     unsigned long address, void *arg)
> @@ -1928,8 +1925,6 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
>   *
>   * Tries to remove all the page table entries which are mapping this page and
>   * replace them with special swap entries. Caller must hold the page lock.
> - *
> - * If is successful, return true. Otherwise, false.
>   */
>  void try_to_migrate(struct page *page, enum ttu_flags flags)
>  {
>