Re: [RFC] mm: change mm_advise_free to clear page dirty

[Minchan Kim <minchan@kernel.org>]

Hello,

On Fri, Feb 27, 2015 at 11:37:18AM +0800, Wang, Yalin wrote:
> This patch add ClearPageDirty() to clear AnonPage dirty flag,
> the Anonpage mapcount must be 1, so that this page is only used by
> the current process, not shared by other process like fork().
> if not clear page dirty for this anon page, the page will never be
> treated as freeable.

In case of anonymous page, it has PG_dirty when VM adds it to
swap cache and clear it in clear_page_dirty_for_io. That's why
I added ClearPageDirty if we found it in swapcache.
What case am I missing? It would be better to understand if you
describe specific scenario.

Thanks.

> 
> Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
> ---
>  mm/madvise.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 6d0fcb8..257925a 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -297,22 +297,17 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
>  			continue;
>  
>  		page = vm_normal_page(vma, addr, ptent);
> -		if (!page)
> +		if (!page || !PageAnon(page) || !trylock_page(page))
>  			continue;
>  
>  		if (PageSwapCache(page)) {
> -			if (!trylock_page(page))
> +			if (!try_to_free_swap(page))
>  				continue;
> -
> -			if (!try_to_free_swap(page)) {
> -				unlock_page(page);
> -				continue;
> -			}
> -
> -			ClearPageDirty(page);
> -			unlock_page(page);
>  		}
>  
> +		if (page_mapcount(page) == 1)
> +			ClearPageDirty(page);
> +		unlock_page(page);
>  		/*
>  		 * Some of architecture(ex, PPC) don't update TLB
>  		 * with set_pte_at and tlb_remove_tlb_entry so for
> -- 
> 2.2.2
> 
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-- 
Kind regards,
Minchan Kim