linux-kernel - Re: [PATCH] mm: change may_enter

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Date:	Fri, 13 Nov 2015 13:01:16 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	yalin wang <yalin.wang2010@...il.com>, akpm@...ux-foundation.org,
	mhocko@...e.cz, vdavydov@...allels.com, hannes@...xchg.org,
	mgorman@...hsingularity.net, tj@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: change may_enter_fs check condition

On 11/13/2015 12:47 PM, yalin wang wrote:
> Add page_is_file_cache() for __GFP_FS check,
> otherwise, a Pageswapcache() && PageDirty() page can always be write
> back if the gfp flag is __GFP_FS, this is not the expected behavior.

I'm not sure I understand your point correctly *), but you seem to imply 
that there would be an allocation that has __GFP_FS but doesn't have 
__GFP_IO? Are there such allocations and does it make sense?

*) It helps to state which problem you actually observed and are trying 
to fix. Or was this found by code inspection? In that case describe the 
theoretical problem, as "expected behavior" isn't always understood by 
everyone the same.

> Signed-off-by: yalin wang <yalin.wang2010@...il.com>
> ---
>   mm/vmscan.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index bd2918e..f8fc8c1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -930,7 +930,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>   		if (page_mapped(page) || PageSwapCache(page))
>   			sc->nr_scanned++;
>
> -		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
> +		may_enter_fs = (page_is_file_cache(page) && (sc->gfp_mask & __GFP_FS)) ||
>   			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
>
>   		/*
>

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