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

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Message-Id: <77563C7C-973D-40CF-8AC3-FA550D349BE2@gmail.com>
Date:	Mon, 16 Nov 2015 09:38:32 +0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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 Nov 13, 2015, at 23:36, Michal Hocko <mhocko@...nel.org> wrote:
> 
> On Fri 13-11-15 13:01:16, Vlastimil Babka wrote:
>> 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?
> 
> No it doesn't. There is a natural layering here and __GFP_FS allocations
> should contain __GFP_IO.
> 
> The patch as is makes only little sense to me. Are you seeing any issue
> which this is trying to fix?
mm..
i don’t see issue for this part ,
just feel confuse when i see code about this part ,
then i make a patch for this .
i am not sure if __GFP_FS will make sure __GFP_IO flag must be always set.
if it is ,  i think can add comment here to make people clear . :)

Thanks

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