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Date:   Mon, 13 Mar 2017 14:34:37 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     "'Minchan Kim'" <minchan@...nel.org>,
        "'Andrew Morton'" <akpm@...ux-foundation.org>
Cc:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <kernel-team@....com>, "'Johannes Weiner'" <hannes@...xchg.org>,
        "'Michal Hocko'" <mhocko@...e.com>,
        "'Kirill A. Shutemov'" <kirill.shutemov@...ux.intel.com>,
        "'Anshuman Khandual'" <khandual@...ux.vnet.ibm.com>
Subject: Re: [PATCH v1 02/10] mm: remove SWAP_DIRTY in ttu


On March 13, 2017 8:36 AM Minchan Kim wrote: 
> 
> If we found lazyfree page is dirty, try_to_unmap_one can just
> SetPageSwapBakced in there like PG_mlocked page and just return
> with SWAP_FAIL which is very natural because the page is not
> swappable right now so that vmscan can activate it.
> There is no point to introduce new return value SWAP_DIRTY
> in ttu at the moment.
> 
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>

>  include/linux/rmap.h | 1 -
>  mm/rmap.c            | 6 +++---
>  mm/vmscan.c          | 3 ---
>  3 files changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index fee10d7..b556eef 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -298,6 +298,5 @@ static inline int page_mkclean(struct page *page)
>  #define SWAP_AGAIN	1
>  #define SWAP_FAIL	2
>  #define SWAP_MLOCK	3
> -#define SWAP_DIRTY	4
> 
>  #endif	/* _LINUX_RMAP_H */
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 9dbfa6f..d47af09 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1414,7 +1414,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>  			 */
>  			if (unlikely(PageSwapBacked(page) != PageSwapCache(page))) {
>  				WARN_ON_ONCE(1);
> -				ret = SWAP_FAIL;
> +				ret = false;
Nit:
Hm looks like stray merge.
Not sure it's really needed. 

>  				page_vma_mapped_walk_done(&pvmw);
>  				break;
>  			}
> @@ -1431,7 +1431,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>  				 * discarded. Remap the page to page table.
>  				 */
>  				set_pte_at(mm, address, pvmw.pte, pteval);
> -				ret = SWAP_DIRTY;
> +				SetPageSwapBacked(page);
> +				ret = SWAP_FAIL;
>  				page_vma_mapped_walk_done(&pvmw);
>  				break;
>  			}
> @@ -1501,7 +1502,6 @@ static int page_mapcount_is_zero(struct page *page)
>   * SWAP_AGAIN	- we missed a mapping, try again later
>   * SWAP_FAIL	- the page is unswappable
>   * SWAP_MLOCK	- page is mlocked.
> - * SWAP_DIRTY	- page is dirty MADV_FREE page
>   */
>  int try_to_unmap(struct page *page, enum ttu_flags flags)
>  {
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a3656f9..b8fd656 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1142,9 +1142,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>  		if (page_mapped(page)) {
>  			switch (ret = try_to_unmap(page,
>  				ttu_flags | TTU_BATCH_FLUSH)) {
> -			case SWAP_DIRTY:
> -				SetPageSwapBacked(page);
> -				/* fall through */
>  			case SWAP_FAIL:
>  				nr_unmap_fail++;
>  				goto activate_locked;
> --
> 2.7.4